!!!!! INVASIVE'PLANT'SPECIES'IMPACTS'ON'CARBON'AND'NITROGEN'CYCLING'IN'INLAND' MICHIGAN'WETLANDS' ' By' ' Jason'Philip'Martina'

Transcription

1 INVASIVEPLANTSPECIESIMPACTSONCARBONANDNITROGENCYCLINGININLAND MICHIGANWETLANDS By JasonPhilipMartina ADISSERTATION Submittedto MichiganStateUniversity inpartialfulfillmentoftherequirements forthedegreeof DOCTOROFPHILOSOPHY PlantBiology Ecology,EvolutionaryBiologyandBehavior 2012

2 ABSTRACT INVASIVEPLANTSPECIESIMPACTSONCARBONANDNITROGENCYCLINGININLAND MICHIGANWETLANDS By JasonPhilipMartina Planttraitsareoftenthecentralfocusofecologicalinvestigationsintoecosystem structureandfunctionbecauseoftheneedtosimplifycomplexplantcommunitiestoafew traitsofimportance.invasionsbyinvasivespeciescanhavemajorimpactsonecosystem functionbyalteringthepresenceand/ordominanceofplanttraitsthatinfluence ecosystemenergyflowandnutrientcycling.thebroadgoalofthisdissertationwasto investigatetheecosystemconsequencesofinvasiveplantspeciesintemperatewetlands, whichareimportantecosystemsforthecyclingofcarbon(c)andnitrogen(n),focusingon Phragmites+australis+(Cav)Trin.ExSteud,+Phalaris+arundinaceaL.andTypha+ glaucagodr. X.IhypothesizedthatwithininlandMichiganwetlands,thedegreeofinvasionwouldbe correlatedwithincreasedcandnstocksduetothehighproductionoflowqualitylitter fromtheseinvasiveplants.ifoundevidencethatbothsoilandecosystemcstocks increasedduetothepresenceoftheseinvasivespecies.additionally,ifoundsignificant differencesforcandnmineralizationamongspecieslinkedtothequalityoftheirlitter (C:Nratios),withP.+australissoilhavingthelowestCandNmineralizationandP.+ arundinaceasoilthehighest. Phragmites+australisisatall,highbiomassinvasivespeciesthatisarelativelyrecent invaderintothewetlandsofthegreatlakesstates.toinvestigatetheeffectsofliving biomassandlitteroncandncycling,imanipulatedp.+australislitterandbiomasswithin

3 plotsatthreewetlandsitesandthenmonitoredabioticconditionsandperformeda numberofbiogeochemicalassays.removingp.+australislitterandbiomasshadthe hypothesizedeffectsofincreasinglightlevelsatthesoilsurfaceandincreasingsoil temperature,thoughtheseeffectsdidnotinfluencelitterbagdecomposition,in+situn mineralization,orpotentialdenitrificationrates.biomassremovaldidaffectporewaterion concentrationsbydecreasingna +,Cl ] andca 2+ concentrationsandincreasingno3 ] concentration.thoughnotinitiallyhypothesized,allcandncyclingratesshowedstrong siteeffectscausedbydifferenthydrologicconditionsamongsites. Toseparatelitterquality,litterdiversity,andsoiloriginfromothercontrolsof decomposition,iperformedtwolaboratoryincubationsusinglitterandsoilcollectedfrom monospecificstandsofthethreefocalinvasivespeciespluscarex+lacustris,anativesedge.i foundsupportformypredictionthatthefourspeciesdifferedinlitterqualityandthatlitter C:NratiowasnegativelyrelatedtoCandNmineralizationrates.Ialsofoundstrongsoil origineffectsrelatedtosoilnutrientavailability,whichhavenotbeenfoundbeforewithina similarexperimentalframework.thesecondincubationshowedthatwhilelitterdiversity significantlyaffectedlitterdecompositionrates,theeffectsweremoredependentofthe identityofthespeciesthanjustthenumberofspecies. Takentogether,theseresultssuggestthatinvasivespeciescaninfluenceCandN cyclingininlandmichiganwetlands,andthatsomeofthebiogeochemicaleffects,like increasedcstorage,couldbeapositiveoutcomeofinvasion.theseeffectscanalsobe linkedtokeyplanttraits,suchaslitterqualityandbiomassproduction,andsupportsthe conjecturethatinvasivespeciesalterecosystemfunctionbychangingthecompositionor dominanceofplanttraitswithinthecommunity.

4 Thisworkisdedicatedtomygrandmother,HelenDombrowski. Thankyouforbelievinginme. iv

5 ACKNOWLEDGEMENTS Iwouldliketothankmyadvisors,Dr.StephenK.HamiltonandDr.MerrittTuretsky, fortheirguidancethroughoutthisproject.theybothshowedgreatpatiencewithme throughouttheentireprocess,especiallywheniwaswriting.withouttheirhelpand supportiwouldn thavebeenabletocompletethistask.iamalsogratefultomy committeemembers,dr.kaygrossanddr.jaylennonfortheirdirectiononexperimental designandcommentsonearlydraftsofthisdissertation.assistancefrommultiplepeople madethisresearchpossible.ihadagreatgroupofundergraduateshelpwiththisproject includingcolinphillippo,spencerrubin,ryano Connor,MattChansler,MattKolp,and ClaireMoore.Iamsoproudofallofthem.Specialthanksgoestoallmembersofthe HamiltonandTuretskyLabs,especiallyDaveWeedforallofhislaboratoryassistance. LeilaSicilianoprovidedadditionalfieldandlaboratoryassistance.Thankstoallthefaculty, graduatestudents,andstaffatmsuandkbswhohavehelpedmegetthroughmyclasses, thesiswriting,andexperimentation.thelistwouldbetoolongtowrite,butyouknowwho youare.thankyou. IwouldalsoliketothankDr.DavidRothsteinandhislabmembers,EllenHolste, MikeCook,andTomBaribault,fortheguidancetheygaveonchemicalanalysisandfor allowingmetoroutinelyusetheirlaboratory.dr.stuartgrandyandcynthiakallenbach alsoallowedmetousetheirlaboratoryandequipment.thankstodr.jentankatthe UniversityofNotreDameandhergraduatestudent,SarahRoley,forguidingmethrough thedenitrificationassays.iamindebtedtodr.carlvonendeatnorthernillinois UniversityforthetraininghegavemebeforeenteringthedoctoralprogramatMSUandfor v

6 statisticalguidance.ahugethankyougoestodr.andyjaroszandhislab,specificallyjosh Springer,fortakingmeinandallowingmetousetheirlabandresourceswhenIhadno whereelsetogo.iwillalwaysvalueourlabmeetingstogetherandfriendship. FundingforthisresearchwasprovidedbyanEnvironmentalProtectionAgency STARFellowship,aSocietyofWetlandScientistsResearchGrant,aLTERSmallGrant,a BiogeochemistryEnvironmentalResearchInitiativeGrant,aCollegeofNaturalScience ContinuationandCompletionFellowship,theMSUGraduateSchool,thePaulTaylor EndowmentFund,theDepartmentofPlantBiology,theKelloggBiologicalStation,andthe Ecology,EvolutionaryBiologyandBehaviorProgram. IamverygratefulforthesupportIreceivedfrommyparents,JosephandJudi Martina,andmybrother,EricMartina.YouareanamazinggroupofpeoplewhoIstriveto bemorelikeeveryday.mostimportantly,iwouldliketothankleilasiciliano.without yourhelp,support,love,andinfinitepatiencenoneofthiswouldhavebeenpossible. vi

7 TABLEOFCONTENTS LISTOFTABLES...ix LISTOFFIGURES... xii CHAPTER1 INTRODUCTION CarbonandNitrogenCyclinginWetlands InvasiveSpeciesandPlantFunctionalTraits Decomposition:AbioticandBioticDeterminants ResearchObjectives...20 CHAPTER2 ORGANICMATTERACCUMULATIONANDQUALITYINMICHIGANWETLANDS: CONSEQUENCESOFINVASIVEPLANTS BriefRationale Objectives,Hypotheses,andPredictions Methods...28 a. Studysitesandsamplingforwetlandsurvey...28 b. Carbonandnitrogenanalysis...30 c. Estimationofplantabundance d. Soilcarbonqualityassay...32 e. Nmineralizationandnitrificationassay...35 f. Statisticalanalyses...37 i. Wetlandsurvey...37 ii. AssaysofCqualityandNtransformations Results...41 a. Wetlandsurvey...41 b. Soilcarbonqualityassay...44 c. Nmineralizationandnitrificationassay Discussion...62 CHAPTER3 EFFECTSOFABOVEGROUNDBIOMASSANDLITTERONBIOGEOCHEMICALCYCLINGIN PHRAGMITES+AUSTRALISSTANDS BriefRationale Objectives,Hypotheses,andPredictions Methods...74 a. Sitedescriptionandexperimentaltreatmentdesign...74 b. Abioticandbioticmeasurements...77 c. Litterbagdecompositionassay...79 d. Porewaterequilibrators...80 e. Nmineralizationandnitrificationassays...81 vii

8 f. Denitrificationassay...82 g. Statisticalanalyses Results...90 a. Sitecharacteristics...90 b. LitterandAGBeffectsonsoilandporewaterchemistry,lightlevels,and temperature...92 c. Carbonandnitrogencycling Discussion CHAPTER4 EFFECTSOFLITTERQUALITY,SOILORIGIN,ANDPLANTSPECIESDIVERSITYON DECOMPOSITIONINTEMPERATEWETLANDS BriefRationale Objectives,Hypotheses,andPredictions Methods a. Litterqualityandsoiloriginincubation i. Sitedescriptionandsampleprocessing ii. Carbonmineralizationassay iii. Nmineralization/nitrificationassay b. Litterdiversityincubation i. Sitedescriptionandsampleprocessing ii. Carbonmineralizationassay iii. Nmineralization/nitrificationassay c. Statisticalanalysis Results a. Litterqualityandsoiloriginincubation b. Litterdiversityincubation Discussion a. Litterqualityandsoiloriginincubation b. Litterdiversityincubation CHAPTER5 CONCLUSIONS APPENDICES AppendixA AppendixB REFERENCES viii

9 LISTOFTABLES Table2]1.GPScoordinatesofthe24surveysiteswiththeirhydrologicalclassification, whichisbasedonmagnesiumconcentrations(seemethodsformoredetails),andthe presenceorabsenceofthemostdominantinvasivespecies.phalaris=phalaris+ arundinacea,typha=typhaxglauca,phragmites=phragmites+australis...40 Table2]2.Summaryofthebest]fitmodelforbiomassCandNstocks.Dominancerefersto theproportionofthetotalbiomassfrominvasiveornativespecies.termsinboldindicate significantpredictors.df(den)indicatesthedenominatordegreesoffreedom Table2]3.Summaryofthebest]fitmodelforlitterCandNstocksandlitterC:Nratios. Termsinboldindicatesignificantpredictors.Df(Den)indicatesthedenominatordegrees offreedom Table2]4.Summaryofthebest]fitmodelforsoilCandNstocksandsoilC:Nratios.Terms inboldindicatesignificantpredictors.df(den)indicatesthedenominatordegreesof freedom Table2]5.Summaryofthebest]fitmodelforecosytemCandNstocks.Termsinbold indicatesignificantpredictors.df(den)indicatesthedenominatordegreesoffreedom...49 Table2]6.ResultsofrepeatedmeasuresANOVAfortheeffectofSpecies,Temperatureand TimeonCmineralizationthroughoutthe36dayincubation...50 Table2]7.SummaryofANOVAexaminingtheeffectofSpeciesandTemperatureon cumulativecmineralization Table2]8.Soilandlitter%C,%N,andC:Nratioofthefourspeciesusedintheorganic matterqualityincubation.samelettersuperscriptdenotesnonsignificantdifferences accordingtotukeyposthoctests.valuesaremeans±se...51 Table2]9Soil%C,%N,andC:NratioofthefourspeciesusedintheN mineralization/nitrificationincubation.samelettersuperscriptdenotesnonsignificant differencesaccordingtotukeyposthoctests.valuesaremeans±se...51 Table3]1.Variationamongsitesinplantcharacteristics,soilcharacteristics,andwater chemistry.varianceexpressedasstandarderror.agb=abovegroundbiomass,do= dissolvedoxygen,spc=specificconductivity,orp=oxidationreductionpotential,om= organicmatter.*indicatesdatacollectedin ix

10 Table3]2.MixedmodelF]valuesfortheeffectofSiteandDepthonBulkDensity, Ammonium,Nitrate,Soil%C,Soil%N,SoilC:Nratio,andSoilCandNStock.dfindicates degreesoffreedom.significanceisdenotedwithasterisk(s)...97 Table3]3.MixedmodelF]valuesfortheeffectofTreatmentandDepthonBulkDensity, Ammonium,Nitrate,Soil%C,Soil%N,SoilC:Nratio,andSoilCandNStock.dfindicates degreesoffreedom.significanceisdenotedwithasterisk(s)...97 Table3]4.Summaryoftwo]factorANOVAfortheeffectofTreatmentandDepthonsoil temperature.dendfindicatesthedenominatordegreesoffreedomandnumdfindicates numeratordegreesoffreedom...98 Table3]5.SummaryofRepeatedMeasuresANOVAfortheeffectofTreatment,Depth,and Timeonsoiltemperatureduringthe2010growingseason.dendfindicatesdenominator degreesoffreedomandnumdfindicatesnumeratordegreesoffreedom Table3]6.MixedmodelF]valuesfortheeffectofTreatmentandDepthonTDP(total dissolvedphosphate),mg 2+,Ca 2+,Na +,K +,SO4 2],Cl ],andno3 ] concentrationsfrom porewaterequilibrators.significanceisdenotedwithasterisk(s).dfindicatesdegreesof freedom Table3]7.Summaryoftwo]factorANOVAsfortheeffectofTreatmentandDepthonstem andfilterdecompositionandsiteanddepthonstemandfilterdecomposition(expressed asfirst]orderrateconstants,k).dendfindicatesthedenominatordegreesoffreedomand numdfindicatesnumeratordegreesoffreedom Table4]1.Averagedecompositionratesexpressedasfirst]orderrateconstants(k;day ]1 ) foreachlitterxsoilorigintreatmentcombination Table4]2.Summaryofthetwo]factorANOVAsfortheeffectofspecies]specificlitterand soilondecompositionconstant(k),cumulativecmineralization,andnmineralization Table4]3.Soilandlitter%C,%N,andC:Nmassratiosofthefourspeciesusedinthelitter qualityandsoiloriginincubation.samelettersuperscriptdenotesnonsignificant differencesaccordingtotukeyposthoctests.valuesaremeans±se Table4]4.Averagedecompositionratesexpressedasfirst]orderrateconstants(k;day ]1 ) foreachlitterdiversitytreatment Table4]5.SummaryofANOVAsfortheeffectofTreatmentondecomposition(K)constant, cumulativecmineralization,andnmineralization Table4]6.LitterC:Nmassratios,%lignin,andlignin:Nmassratiosofthefourspeciesused inthelitterdiversityincubation.samelettersuperscriptdenotesnonsignificant differencesaccordingtotukeyposthoctests.valuesaremeans±se x

11 TableA]1.ModelsofBiomassCStock.Modelinboldindicatesthebest]fitmodelbasedon lowestaicvalue TableA]2.ModelsofBiomassNStock.Modelinboldindicatesthebest]fitmodelbasedon lowestaicvalue TableA]3.ModelsofLitterCStock.Modelinboldindicatesthebest]fitmodelbasedon lowestaicvalue TableA]4.ModelsofLitterNStocks.Modelinboldindicatesthebest]fitmodelbasedon lowestaicvalue TableA]5.ModelsofLitterC:Nratio.Modelinboldindicatesthebest]fitmodelbasedon lowestaicvalue TableA]6.ModelsofSoilCStock.Modelinboldindicatesthebest]fitmodelbasedon lowestaicvalue TableA]7.ModelsofSoilNStocks.Modelinboldindicatesthebest]fitmodelbasedon lowestaicvalue TableA]8.ModelsofSoilC:N.Modelinboldindicatesthebest]fitmodelbasedonlowest AICvalue TableA]9.ModelsofEcosystemCStock.Modelinboldindicatesthebest]fitmodelbased onlowestaicvalue TableA]10.ModelsofEcosystemNStock.Modelinboldindicatesthebest]fitmodelbased onlowestaicvalue TableA]11.Best]fitmodelsummarytableforeachdependentvariable xi

12 LISTOFFIGURES Figure1]1.Interactionsbetweenplantcommunitycomposition(PCC),planttraitsandsoil microenvironmentinfluenceecosystemprocesses.plantcommunitycompositioneffects oncandncyclingaremediatedthoughplanttraitsdirectly(plantnuptake)andindirectly (substratequalityandsoilmicroenvironmentalteration).invasivespeciesintroducenovel planttraitsintoacommunityandpotentiallycanalterecosystemfunction.arrows representpathwaysofinfluenceandareaddressedinthetext...23 Figure2]1.Regressionbetweeninvasivespeciesdominance(percentbiomassof community)andshannondiversityindex(adjustedr 2 =0.75,p<0.001)...52 Figure2]2.Regressionbetweeninvasivespeciesbiomass(cumulativebiomassof Phragmitesaustralis,Phalaris+arundinacea,and+Typhaspp.)andsitenitrogenuseefficiency (adjustedr 2 =0.10,p=0.08)...53 Figure2]3.Regressionbetweeninvasivespeciesbiomass(cumulativebiomassof Phragmitesaustralis,Phalaris+arundinacea,and+Typhaspp.)andtotalbiomass(adjustedR 2 =0.61,p<0.001)...54 Figure2]4.Regressionbetweenbiomass%NandlitterC:Nratio(adjustedR 2 =0.32,p< 0.001).Biomass%Nwasasignificantpredictorinthebest]fitmodelforlitterC:Nratios. 55 Figure2]5.Regressionbetweeninvasivespeciesbiomass(cumulativebiomassof Phragmitesaustralis,Phalaris+arundinacea,and+Typhaspp.)andsoilCstock(adjustedR= 0.27,p<0.001).Invasivespeciesbiomasswasasignificantpredictorinthebest]fitmodel forsoilcstock Figure2]6.Regressionbetweeninvasivespeciesbiomass(cumulativebiomassof Phragmitesaustralis,Phalaris+arundinaceaand+Typhaspp.)andecosystemCstock (adjustedr 2 =0.35,p<0.001).Invasivespeciesbiomasswasasignificantpredictorinthe best]fitmodelforecosystemcstock...57 Figure2]7.Carbonmineralizationratesoverthe36]daylaboratoryincubation.Repeated measuresanovashowedthattherewasasignificant3]wayinteractionbetweenspecies, temperatureandtime(f2,494=7.00,p=0.001).errorbarsrepresent1se...58 Figure2]8.MeancumulativeCmineralizationoverthe36]daylaboratoryincubation.The maineffectsofspecies(f2,8=5.82,p=0.028)andtemperature(f2,47= ,p<0.001) xii

13 weresignificant,butnottheirinteraction.samelettersuperscriptdenotesnonsignificant differencesaccordingtotukeyposthoctests.errorbarsrepresent1se...59 Figure2]9.RegressionbetweensoilC:NratioandcumulativeCmineralizationathigh (21 C;adjustedR 2 =0.53,p<0.001)andlow(7 C;adjustedR 2 =0.40,p<0.001) temperatures Figure2]10.ComparisonofmeanQ10valuesamongsoilcollectedfrommonospecific standsofphragmites+australis,phalaris+arundinacea,andtyphaspp.theeffectofspecies wasmarginallysignificant(f2,8=3.46,p=0.082).errorbarsrepresent1se...61 Figure2]11.ComparisonofmeannetNmineralizationratesamongsoilcollectedfrom monospecificstandsofphragmites+australis,phalaris+arundinacea,andtyphaspp.the effectofspecieswassignificant(f2,5=22.32,p=0.003).samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se...61 Figure3]1.MapshowingthelocationofthetwomonospecificstandsofPhragmites+ australisatlakelansingpark(llp1andllp2),haslett,mi Figure3]2.MapshowingthelocationofthemonospecificstandofPhragmites+australisin thewetlandareasurroundingglasbylake(glasby),delton,mi...89 Figure3]3.WatertablepositionatGlasbyandLLP1fromJulytoOctoberof2008.Zero waterlevelrepresentsthesoilsurfacewithpositivewaterlevelsindicatingflooding (standingwater)andnegativevaluesindicatingawatertablebelowthesoilsurface Figure3]4.WatertablepositionatGlasby,LLP1,andLLP2fromAugusttoNovemberof 2009.Zerowaterlevelrepresentsthesoilsurfacewithpositivewaterlevelsindicating flooding(standingwater)andnegativevaluesindicatingawatertablebelowthesoil surface Figure3]5.WatertablepositionatGlasby,LLP1,andLLP2fromJulytoOctoberof2010. Zerowaterlevelrepresentsthesoilsurfacewithpositivewaterlevelsindicatingflooding (standingwater)andnegativevaluesindicatingawatertablebelowthesoilsurface Figure3]6.WatertablepositionatGlasby,LLP1,andLLP2for2008to2010(seemethods forexacttimeperiods).zerowaterlevelrepresentsthesoilsurfacewithpositivewater levelsindicatingflooding(standingwater)andnegativevaluesindicatingawatertable belowthesoilsurface.errorbarsrepresent1standarddeviation Figure3]7.Meanlightlevels(PAR)measureddirectlyabovethesoilsurfacewithincontrol (C),biomassremoval(BR),litterremoval(LR),andtotalremoval(TR)treatmentplots averagedacrosssites.therewasasignificanttreatmenteffect(f3,81=109.95,p<0.001). SamelettersuperscriptdenotesnonsignificantdifferencesaccordingtoTukeyposthoc tests.errorbarsrepresent1se xiii

14 Figure3]8.Meanmanualtemperaturemeasurementstakenat6soildepths(andambient) withincontrol(c),biomassremoval(br),litterremoval(lr),andtotalremoval(tr) treatmentplotsaveragedacrosssites.therewasasignificantinteractionbetween treatmentanddepth(f18,174=2.07,p<0.009).samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se.106 Figure3]9.DailyambientmeantemperaturefromJulytoOctober2010withincontrol(C), biomassremoval(br),litterremoval(lr),andtotalremoval(tr)treatmentplots Figure3]10.DailysoilsurfacemeantemperaturefromJulytoOctober2010withincontrol (C),biomassremoval(BR),litterremoval(LR),andtotalremoval(TR)treatmentplots Figure3]11.Dailymeantemperatureat2cmsoildepthfromJulytoOctober2010within control(c),biomassremoval(br),litterremoval(lr),andtotalremoval(tr)treatment plots Figure3]12Dailymeantemperatureat10cmsoildepthfromJulytoOctober2010within control(c),biomassremoval(br),litterremoval(lr),andtotalremoval(tr)treatment plots Figure3]13.MeanCl ] concentrationsfromporewaterequilibratorswithincontrol(c), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectoftreatment(F2,63=17.34,p<0.001)onCl ] concentrations, butnotdepthortheirinteraction.errorbarsrepresent1se Figure3]14.MeanNa + concentrationsfromporewaterequilibratorswithincontrol(c), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectoftreatment(F2,63=4.93,p=0.01)onNa + concentrations, butnotdepthortheirinteraction.errorbarsrepresent1se Figure3]15.MeanMg 2+ concentrationsfromporewaterequilibratorswithincontrol(c), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectoftreatment(F2,63=3.29,p=0.043)anddepth(F13,63= 9.20,p<0.001)onMg 2+ concentrations,butnottheirinteraction.errorbarsrepresent1 SE Figure3]16.MeanCa 2+ concentrationsfromporewaterequilibratorswithincontrol(c), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectoftreatment(F2,63=7.54,p=0.001)anddepth(F13,63= 5.44,p<0.001)onCa 2+ concentrations,butnottheirinteraction.errorbarsrepresent1 SE xiv

15 Figure3]17.MeanSO4 2] concentrationsfromporewaterequilibratorswithincontrol(c), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectofdepth(F13,63=4.48,p<0.001)onSO4 2] concentrations, butnottreatmentortheirinteraction.errorbarsrepresent1se Figure3]18.MeanNO3 ] ]Nconcentrationsfromporewaterequilibratorswithincontrol(C), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectofdepth(F13,63=3.16,p=0.049)andtreatmentonNO3 ] (F13,63=2.91,p=0.002)concentrations,butnottheirinteraction.Errorbarsrepresent1 SE Figure3]19.MeannetNmineralizationratesamongsoilcollectedwithinmonospecific standsofphragmites+australisatglasby,llp1,andllp2.theeffectofsitewassignificant (F2,87=65.57;p<0.001).Samelettersuperscriptdenotesnonsignificantdifferences accordingtotukeyposthoctests.errorbarsrepresent1se Figure3]20.Meannetnitrificationratesamongsoilcollectedwithinmonospecificstands ofphragmites+australisatglasby,llp1,andllp2.theeffectofsitewassignificant(f2,87= 1.29;p<0.001).Samelettersuperscriptdenotesnonsignificantdifferencesaccordingto Tukeyposthoctests.Errorbarsrepresent1SE Figure3]21.Regressionbetweensoil%moistureandnetNmineralizationrates(adjusted R 2 =0.297,p<0.001) Figure3]22.Regressionbetweensoil%moistureandnetNmineralizationrates(adjusted R 2 =0.406,p<0.001) Figure3]23.Regressionbetweensoil%moistureandnetNmineralizationrates(adjusted R 2 =0.125,p<0.001) Figure3]24.Meanfirstorderrateconstants(k;day ]1 )forstemsincubatedwithincontrol (C),biomassremoval(BR),litterremoval(LR),andtotalremoval(TR)treatmentplotsover a90daytimeperiodaveragedacrosssites.therewasasignificanteffectofdepth(f1,44= 6.43;p=0.014),butnottreatmentortheirinteraction.Samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se.119 Figure3]25.Meanfirstorderrateconstants(k;day ]1 )forfiltersincubatedwithincontrol (C),biomassremoval(BR),litterremoval(LR),andtotalremoval(TR)treatmentplotsover a90daytimeperiodaveragedacrosssites.therewasasignificanteffectofdepth(f1,44= xv

16 6.43;p<0.001),butnottreatmentortheirinteraction.Samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se.120 Figure3]26.Meanfirstorderrateconstants(k;day ]1 )forstemsincubatedatglasby(gl), LLP1,andLLP2sitesovera90daytimeperiod.Therewasasignificantinteraction betweensiteanddepth(f2,54=5.12;p=0.009).samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se.120 Figure3]27.Meanfirstorderrateconstants(k;day ]1 )forfiltersincubatedatglasby(gl), LLP1,andLLP2sitesovera90daytimeperiod.Therewasasignificantinteraction betweensiteanddepth(f2,54=10.33;p<0.001).samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se.121 Figure3]28.Meandenitrificationrates(N2Oproduction)amongsoilcollectedwithin monospecificstandsofphragmites+australisatglasby,llp1,andllp2.theeffectofsite wassignificant(f2,27=11.41;p<0.001).samelettersuperscriptdenotesnonsignificant differencesaccordingtotukeyposthoctests.errorbarsrepresent1se Figure3]29.Regressionbetweennitrateanddenitrificationrates(N2O production)(adjustedr 2 =0.310,p<0.001) Figure3]30.RegressionbetweensoilC:Nratioanddenitrificationrates(N2Oproduction) (adjustedr 2 =0.252,p<0.001) Figure4]1.MapshowingthelocationofthemonospecificstandsofPhragmites+australis+ (Phr),+Phalaris+arundinacea+(Pha),+Typha glauca+(typ),+and+carex+lacustris(car)inthe wetlandareawithinlakelansingparknorth,haslett,mi Figure4]2.MeancumulativeCmineralizationoverthe68]daylitterqualityandsoilorigin laboratoryincubation.themaineffectsofspecies]specificlitter(f3,80=69.43,p<0.001) andsoilorigin(f3,80=11.29,p<0.001)weresignificant,butnottheirinteraction.same lettersuperscriptdenotesnonsignificantdifferencesaccordingtotukeyposthoctests. Errorbarsrepresent1SE Figure4]3.RegressionbetweensoilC:NratioandcumulativeCmineralization(all treatments)(adjustedr 2 =0.003,p=0.423) Figure4]4.RegressionbetweensoilC:NratioandcumulativeCmineralization(nolitter treatmentsonly)(adjustedr 2 =0.077,p=0.105) xvi

17 Figure4]5.Regressionbetweensoil%NratioandcumulativeCmineralization(nolitter treatmentsonly)(adjustedr 2 =0.192,p=0.018) Figure4]6.RegressionbetweenlitterC:NratioandcumulativeCmineralization(litter additiontreatmentsonly)(adjustedr 2 =0.524,p<0.001) Figure4]7.RegressionbetweenlitterC:Nratioandday1Cmineralization(Litteraddition treatmentsonly)(adjustedr 2 =0.861,p<0.001) Figure4]8.MeannetNmineralizationoverthe68]daylitterqualityandsoilorigin laboratoryincubation.themaineffectsofspecies]specificlitter(f3,100=92.30,p<0.001) andsoilorigin(f12,100=14.07,p<0.001)weresignificant,butnottheirinteraction.same lettersuperscriptdenotesnonsignificantdifferencesaccordingtotukeyposthoctests. Errorbarsrepresent1SE Figure4]9.RegressionbetweenlitterC:NratioandnetNmineralization(adjustedR 2 = 0.452,p<0.001) Figure4]10.MeancumulativeCmineralizationoverthe55]daylitterdiversitylaboratory incubation.themaineffectoflittertreatmentwassignificant(f14,90=8.08,p<0.001). SamelettersuperscriptdenotesnonsignificantdifferencesaccordingtoTukeyposthoc tests.errorbarsrepresent1se Figure4]11.RegressionbetweenlitterC:NratioandcumulativeCmineralization(adjusted R 2 =0.131,p<0.001) Figure4]12.Regressionbetweenlitter%ligninandcumulativeCmineralization(adjusted R 2 =0.228,p<0.001) Figure4]13.Regressionbetweenlitterlignin/NratioandcumulativeCmineralization (adjustedr 2 =0.313,p<0.001) Figure4]14.RegressionbetweenlitterspeciesdiversityandcumulativeCmineralization (adjustedr 2 =0.075,p=0.002) Figure4]15.MeannetNmineralizationoverthe55]daylitterdiversitylaboratory incubation.themaineffectoflittertreatmentwassignificant(f15,96=845.21,p<0.001). Onlythenolittertreatmentwassignificantlydifferentfromtheothertreatment combinations.errorbarsrepresent1se xvii

18 Chapter1 Introduction CarbonandNitrogenCyclinginWetlands Human]inducedalterationtoglobalbiogeochemicalcyclesiscreatingconsiderable publicandscientificinteresttoday.ofspecialconcernaretheanthropogenicactivitiesthat havedirectlyandindirectlyincreasedtheamountofreactivenitrogen(n)(no3 ] andnh4 + ; Gallowayetal.2003)enteringterrestrialandaquaticecosystems,dueto:(1)increased cultivationofleguminouscropsthatbiologicallyfixun]reactiven(n2)toammonium,(2) combustionoffossilfuelsresultinginthecreationofnoxspecies,and(3)theuseoflarge quantitiesofnh4 + ]basedfertilizerstoincreasecropyieldworldwide(vitouseketal.1997; Driscolletal.2003;Gallowayetal.2003).Theseinputshavecontributedtoelevatedlevels ofreactiventhatresultinmajorecologicalandhumanhealthproblems,suchas troposphericozoneformation,acidrain,highammonium]ntoxicitytofish,carcinogenic effectsofincreasednitratelevelsindrinkingwater,andstimulationofpathogenicmicrobes whichcancausepublichealthrisks(vitouseketal.1997;driscolletal.2003;gallowayet al.2003;zedler2003).aquaticecosystemsareparticularlysensitivetonutrientloading, whichcanresultineutrophication,algalblooms,highbiologicaloxygendemand,andthe formationofdeadzones(livingston2000). Carboncyclingalsohasbeensignificantlyimpactedbyhumanactivities,suchasthe useofcombustionengines,theprocessingofnaturalgasandcrudeoil,anddeforestation (Hoffertetal.1998).TheseactionshaveresultedinrisingconcentrationsofCO2andCH4 1

19 intheatmosphere.bothco2andch4aregreenhousegasesandarehypothesizedtodrive mostoftheanthropogenicclimatechangenowunderway(inadditionton2o),and, therefore,understandinghowtheycyclethroughtheenvironmentisofgreatimportance. Whilethemajorityofthecarboninthebiosphereisstoredintheworld socean,primarily asbicarbonate(schlesinger1997),therehasbeensubstantialinterestinunderstandingthe dynamicsofterrestrialcarbonsourcesandsinksbecausetheyarepotentiallyveryactive andthuscanhavesignificantimpactsoncarboncycling.heimannandreichstein(2008) suggestedthatonaglobalscaleterrestrialecosystemswillprovideapositivefeedbackto globalwarming,mainlybypermafrostthawing,themicrobialprimingeffect,andthe interactionbetweencarbonandnitrogencycles,thoughthemagnitudeofeffectsisless wellknown.soilsarethelargestterrestrialcarbonpool,thoughlivingplants(trees, grasses,etc.)arealsoasignificantpoolofterrestrialcarbon.althoughforestandgrassland soilscanstoreorganicmatterforlongperiodsoftime,wetlands,byfar,storethelargest amountofcarbononanarealbasis,storingaglobaltotalofapproximately billiontonsofcarbon(bridghametal.2006),withthemajorityinnorthernpeatlands. Wetlandsaresignificantsinksofcarbonduetotheirhighproductivityandanaerobic conditionsthatpromoteslowdecomposition,thusresultinginthebuildupoforganic matter.eulissetal.(2006)estimatedthatnorthamericanprairiewetlandrestoration alonehasthepotentialtosequester378tgofcarbonovera10]yeartimeperiod,offsetting theannualfossilfuelcarbonemissionsinnorthamericaby2.4%. ThereisastrongcouplingbetweenCandNcycling(Schlesinger2011).Thisstrong couplingoccursfortwomainreasons:(1)thereisastoichiometricrequirementofcandn 2

20 formostorganisms,solimitationofoneelementwillusuallylimitthecyclingoftheother (assimilatorycoupling)and(2)themetaboliccapabilitiesofmanymicrobesallowforthe catalysisofenergyreleasingreactions,usuallybymeansofchangesinoxidationstatesofc orn(dissimilatorycoupling)(burginetal.2011).indissimilatoryreactions,theelements arenotincorporatedintothebiomassoftheorganismandareinsteadreleaseddirectly backintotheenvironment.thecouplingofcandncyclingcanhaveconsequencestothe structureandfunctionofmanyecosystems.forexample,inalaboratoryincubationusing soilcollectedfromanold]growthconiferoussoil,hartetal.(1994)foundastrongpositive relationshipbetweenco2evolutionandgrossnmineralization.microbialgrowth efficiencydeclinedovertheincubationperiod(456days)suggestingtheuseoflower qualitysubstratesascavailabilitydeclined.thomasetal.(2010)studiedtheeffectsofn depositiononnortheasternforestsandfoundthatndepositionincreasedthegrowthofthe majorityofstudyspecies,andthusincreasedtreecstorage.inwetlands,oneofthebest examplesofthetightcouplingbetweencandnisthedenitrificationprocess.inlow oxygenconditions,denitrifierscanconvertno3 ] ton2oandn2byaseriesofredox reactionsthatuseno3 ] asanelectronacceptorandorganiccarbonasanelectrondonor. Thisisoneofseveralmetabolicpathwaysresponsibleforthedecompositionoforganic matterinanoxicconditions. Wetlandsareusuallyfoundindepressionalareasonthelandscapeandasaresult theyreceivelargeamountsofwaterfromsurfaceandgroundwaterinflow,makingthem vulnerabletoflooding,nutrientloading,andothertypesofdisturbance(zedlerand Kercher2004).Wetlandsaredefinedasecosystemsontheinterfacebetweenterrestrial 3

21 andaquatichabitats(mitschandgosselink2000).thethreemainfeaturesthatdistinguish awetlandare:(1)azoneofsaturation(atthesoilsurfaceorwithintherootingzone)forat leastpartoftheyear,(2)uniquesoilcharacteristicsarisingfromsaturation(e.g.,gleying) and(3)thepresenceofhydrophytes(plantsadaptedtosaturatedsoilconditions)withthe exclusionofplantsintoleranttowaterlogging(mitschandgosselink2000).while wetlandsprovideahostofecosystemservicessuchaswildlifehabitat,floodcontrol,and shorelinestabilization(zedler2003),oneofthemainservicesprovidedbythese ecosystemsistheenhancementofwaterqualityviatheretentionandremovalofexcessn (SaundersandKalff2001;Zedler2003;Verhoevenetal.2006).Wetlandshaveplayed majorrolesofimprovingwaterqualityinanumberofclimatic,ecological,andland]use settings(zedler2003).wetlandsretainandremoventhroughseveralphysicaland biologicalprocesses,includingnretentionviaplantnuptakeformetabolicprocesses, cationexchangeinorganic]richsoils,andlonger]termsedimentationandburial(reddy anddelaune2008).microbially]mediatedtransformationsofninwetlands,including mineralization,nitrification,anddenitrification,areparticularlyimportantbecausethese processesresultintheconversionofreactiventolessreactivespecies(n2oandn2)that areemittedtotheatmosphere. Wetlandsfurnishecosystemservicesdisproportionatelytotheirarea,particularlyin thecaseofwaterqualityimprovement(zedler2003;verhoevenetal.2006).nitrogen retentionandremovalbywetlandshasreceivedparticularattentioninnorthamericaand EuropewhereexcessiveNisaconcern.Wetlandscanreducetheecologicalandhealth risksposedbyexcessninaquaticecosystems,especiallyinareaswhereagricultureor otherlandusescreaterunoffofnoriginatingfromfertilizers(verhoevenetal.2006). 4

22 WetlandNcyclingissensitivetochangesinsoiltemperature,redoxstatus,available nutrients,andph(reddyanddelaune2008)(figure1]1;pathways5,6,and8).because oftheirroleaslandscapesinksfornutrientsandorganicmatter,alongwithhavingperiods ofdryingandrewetting,wetlandsasknownasbiogeochemical hotspots forn(mcclainet al.2003).wetlandsareveryproductiveecosystems,andinmostcases,ratesof photosynthesis(primaryproduction)aregreaterthandecompositioncreatingorganic matterrichsoilthatcontainsnutrientsaswellaselectrondonors(carbon)neededfor manyntransformationprocesses.forexample,nitrification,themicrobially]mediated conversionofammoniumtonitrate,needsanaerobicenvironmentandammoniumto occur.conversely,denitrificationrequiresnitrateastheoxidant,labileorganiccarbonas theelectrondonor,andananaerobicenvironment.thesecontrastingrequirementslimit therateofthesencyclingprocessesinmostecosystems,butwetlandsprovideaerobicand anaerobicconditionsthatvaryspatiallyand/ortemporally,whichcangreatlyincreasethe ratesofprocesseslikedenitrification.(mcclainetal.2003;reddyanddelaune2008). Despitetheirbenefitstowaterquality,themajorityofthewetlandsintheUnitedStates havebeendrainedordegraded,oftenforagriculturalpurposes(zedler2003).overthe pastseveraldecades,mitigationandconservationprogramsintheunitedstateshavebeen establishedtoprotectremainingwetlands,thoughtheyremainvulnerabletoperturbations suchaschangesinnaturalhydrologicflowandnutrientloadingfromsurroundingland] uses(saundersandkalff2001;zedler2003;verhoevenetal.2006).inthegreatlakes region,anareadominatedbywetlands,water,andwater]basedrecreation,increasing invasionsbyexoticspeciesareconsideredtobeoneofthemostcriticalthreatsto biodiversityandecosystemstability(zedlerandkercher2004). 5

23 Wetlandsareespeciallyvulnerabletobiologicalinvasionsbecauseoftheirlandscape settingwheretheyoftenreceiveinflowsofwaterandpropagules,andbecausetheyoften areperiodicallydisturbedbyfloodinganddryingevents(zedlerandkercher2004;magee andkentula2005).whilewetlandplantscanbeconsideredstress]tolerators(grime2002) becausetheyareadaptedtoenvironmentsthatarehighlyvariable(e.g.,seasonally flooded),humanshaveintroducedadditionaldisturbances,suchasnutrientloading,that nativespeciesarenotadaptedto.nutrientloadingusuallyfavorsspeciesthatrespond positivelytohighnutrientavailability(davisetal.2000),whichisthecaseformost wetlandinvasiveplants.recentresearchhasshownthattall,clonalspecieswithrunner behavior(i.e.,specieswithlongspacersbetweenramets,whichincludesmostwetland invasiveplantspecies)respondtonitrogenadditionbyincreasinginabundance,while short,clumpingspecies(manynativewetlandplantspecies)decreasedinabundance (Goughetal.2012).Thismaybeoneofthemainmechanismsfortheinvasibilityof wetlands. Wetlandplantsinfluencewetlandsoilsandhydrologythroughtheirstructure,life history,degreeofclonality,rootcharacteristics,andquantityoflitterinputs(ehrenfeld 2003)(Figure1]1;pathways2and3).Plantsandtheirlitterinfluenceabioticfactors(e.g., wateravailabilityand/orsoiltemperature),therebyindirectlyaffectingmicrobial decompositionratesandsoilcarbonsequestration(evinerandchapin2003;eulissetal. 2006;Lal2008).Forexample,FiskandSchmidt(1995)foundthatrelationshipsbetweenN mineralization,soiltemperature,andwaterinalpinetundracommunitiesvariedamong plantcommunities.itispossiblethatinvasionbyhigh]productivityplantspeciesthat generatelowqualitylittercouldincreasecandnstorage,therebyenhancinganecosystem 6

24 serviceprovidedbywetlands.ameta]analysisof94experimentalstudiesacrossavariety ofecosystemsfoundthatinvasivespeciesinfluencecandncyclingbyincreasingcstocks (rootandshoot),plantnconcentration,andinorganicnpoolsinthesoil,and,althoughthis patternwasnotinfluencedbyecosystem,therewasvariationinthestrengthofeffect amongplantfunctionaltypes(liaoetal.2008). Asmentionedabove,wetlandhydrologyhasgreatinfluenceonthestructureand functionofwetlands(hamilton2002;trebitzetal.2005;sierszenetal.2006).directly, floodingdecreasestheoxygenconcentrationwithinsoilorsediment,whichhas implicationsforsoilrespirationanddecomposition(vandervalk1991;necklesandneill 1994).Thereductionofavailableoxygenduetoflooding,andthereforeareductionin decomposition,isoneofthemainreasonwetlandsaccumulateorganicmatterintheirsoils orsediments.floodingnotonlychangesecosystemprocessesdirectly(e.g.,prolongedsoil anaerobiosis),butalsoindirectlythroughinfluenceontheplantcommunitycomposition. Becausefloodingcanbeacommondisturbanceinwetlands,manystudieshavefocusedon howfloodingcanaffectwetlandplantcommunities(e.g.,hudon2004;kercherandzedler 2004).Whilemostwetlandplantscansurviveperiodsofinundation,plantspeciesvaryin theirtolerancetothedurationanddepthofflooding(cronkandfennessy2001).this variationinfloodtoleranceamongspeciesisoneofthemaincausesfordifferencesinplant communitycompositionamongwetlands(sharitzandpennings2006).floodingcauses multiplechallengesforplantspecies:(1)oxygendiffuses10,000xslowerinwaterthanin air,thusrootsareoxygenlimited,(2)anaerobicconditionsproducetoxicsubstancessuch asfe(ii),h2s,andorganicacidsthatcanharmplantroots,and(3)completesubmergence oftheplantwillleadtoareductionoflight,co2,andoxygentotheshoots(cronkand 7

25 Fennessy2001).Wetlandplantshavemultipleadaptationstocopewithfloodingstress, includingpassivelyoractivelytransportingoxygenfromtheshootstotherootsforroot respiration,releasingoxygenfromthesurfaceoftherootcreatinganoxicenvironmentthat protectstherootfromfe(ii)andh2s,and,inmanycases,tall,emergentstaturethat ensuresdirectinterfacewiththeatmosphereinmostconditions.theeffectoffloodingon wetlandplantcommunitycompositioncantheninfluenceecosystemfunctionbyaltering thepredominantplanttraitswithinthecommunity. InvasiveSpeciesandPlantFunctionalTraits Thehuman]causedredistributionofspecieshasrecentlyacceleratedwiththe economicglobalizationofhumansociety(theoharidesanddukes2007).invasionsby exoticspeciesareconsideredtobeoneofthemostcriticalthreatstobiodiversityand ecosystemstability(walkerandsteffen1997).invasivespeciesthreatenecosystem functiononmultiplelevelsresultingineconomiccostsandecologicaldamage.thecostof damage,control,andremovalofinvasivespeciesreachesapproximately$137billion annuallyfortheunitedstates(pimenteletal.2000,2004).theresultingeffectsofspecies redistributioncausedbytheintroductionofexoticspeciesonecosystem]levelprocesses arelargelyunknown.whileasmallpercentofintroducedspeciesbecomeestablished,with anevensmalleramountbecominginvasive(williamsonandfitter1996),thosespecies thatinvadesuccessfullyoftenbecomedominantandcanaltercommunitystructureand composition(levineetal.2002).forexample,garlicmustard(alliaria+petiolata)invasion intonorthamericanwoodlandshasresultedinthealterationofunder]storyplant communities(meekinsandmccarthy2000;stinsonetal.2007).closerexaminationalso 8

26 hasshownthatgarlicmustardmaychangethetreecommunitytomoreshadetolerant specieswhoseseedlingscanwithstandtheintenseshadingcreatedbygarlicmustard stands(stinsonetal.2007).inaddition,garlicmustardproducesallelopathicchemicals thatinhibitthegrowthotherplants,potentiallyviainhibitionofmycorrhizalfungi(weir 2007). Whilemuchresearchhasinvestigatedwhycertainplantspeciesbecomeinvasivewhile othersdonot,itisnotentirelyclearwhatmechanismsareresponsibleforinvasionsuccess. Someofthemostsupportedhypothesesincludetheenemyreleasehypothesis,broader tolerancehypothesis,efficientusehypothesis,hybridvigorhypothesis,andallelopathy hypothesis(zedlerandkercher2004),thoughnonecanexplainallinvasions.thereis muchevidencethatpropagulepressureisastrongdeterminantofinvasionsuccess (Lockwoodetal.2005),andmorerecenttheorysuggeststhatinvasionisacomplexprocess withmanystagesincludingtransport,introduction,establishment,andspread(blackburn etal.2011).thespreadofinvasivespecieshavealsobeenconnectedtoeconomicactivity; TaylorandIrwin(2004)wereabletoexplain75%ofthevariationinthenumberofexotic plantsinthe50stateswithapopulation]economicmodelthatincorporatedhuman populationandrealestate. Therearealsocontrastingpatternsfortheeffectofinvasivespeciesonspecies diversity.onaglobalscaleitseemsclearthatspeciesdiversityisdecreasingasaresultof manyhumanactivities,suchashabitatdestruction,over]hunting,andspeciesintroductions (KerrandCurrie1995).Onalocalscale(studysiteslessthanafewdozenhectares) specieslossseemstofollowthegeneralglobalpattern;speciesintroductionsdecrease speciesrichness(saxandgaines2003).thepatternforregionalscales(betweenglobal 9

27 andlocalscale)isquitedifferent,asthereseemtobediversityincreasesassociatedwith speciesintroductions(saxandgaines2003).thiscontrastingeffectofintroducedspecies isnoteasilyexplained,thoughtheregionalincreaseislikelypartiallycausedbyspecies redistributionbyhumans,increasingthetotalnumberofspeciesonacontinentalscale, whileatthelocalscaleinvasivespeciesareknowntocompetitivelyexcludemostother specieswheretheyoccur.thedecreaseinspeciesdiversityatalocalscaleisalsomore severeinanthropogenicenvironments(saxandgaines2003).anotherparadoxrelated withscaleisthepositiveassociationfoundbetweennativesandexoticspeciesrichnessat broadscalescontrastedwiththenegativeassociationsatfinescales(fridleyetal.2007). Theseparadoxesshowourincompleteunderstandingofspeciesinvasionsandseemto suggestthatmorefocusedstudiesareneededtoresolvethesedilemmas.regardlessofthe mechanismofthesepatterns,itisclearthatinvasivespeciesnegativelyimpactspecies diversityonglobalandlocalscales. Whenaninvasiveplantbecomeslocallydominant,itcandirectlyandindirectlyimpact theinvadedcommunity(figure1]1).invasiveandresidentspecieslikelydifferinkeyplant traitssuchastissuequality,productivity(above]andbelow]ground),andphenology. Ecosystemprocessesaresensitivetotheidentityofplantspeciesthatcomprisecommunity speciespools(evinerandchapin2003),thusinvasionsintonaturalcommunitiescanalter ecosystem]levelprocessesbyintroducingnovelplanttraitsthatinfluencesoil environments,soilmicroorganismcomposition,and/ornutrientcycling.inamixed deciduousforestinnewyorkitwasshownthatinvasivewoodyspeciesaccelerated decompositionrates,whichinturnresultedinincreasednlossfromlitter(ashtonetal. 2005).Whatwasinterestingaboutthisstudywasthatalllitterintheinvadedsites(exotic 10

28 andnativespecies)decomposedfastercomparedtothenon]invadedsites.thisshowed thatspecies]specificlitterdecompositionwasnottheonlyimportantdifferencebetween invadedandnon]invadedsitesandthatinvasivespeciesindirectlyaffectedecosystem processes(ashtonetal.2005). Variationinplanttraitswithinacommunityisknowntoinfluencemanyaspectsof ecosystemfunction(chapin2003).biomassaccumulationandotherplanttraitsthataffect organicmatterqualitycandirectlyandindirectlyinfluenceanecosystem sabilitytostore carbon(c)andnitrogen(n)withinlitterandsoillayers(ehrenfeld2003).previouswork hasshownthatplantfunctionalgroupdiversityhadstrongeffectsontotalplantn,plant productivity,andlightpenetrationinanexperimentalgrasslandinminnesota(tilmanetal. 1997),whilefunctionalgroupcompositionwasamoreimportantpredictorofecosystem] levelprocessesthanfunctionalgrouprichnessinaserpentinegrasslandincalifornia (HooperandVitousek1997).Plantfunctionaltraitssuchasleaftissuechemistry,rooting depth,andcanopystructureaffectecosystemproductivityandcandncycling(tilmanet al.1997;ehrenfeld2003;evinerandchapin2003). Plantfunctionaltraitsareusefultostudybecausetheyallowustosimplifycomplex andseeminglyspecies]specificcontrolsonecological/biogeochemicalprocessestoafew planttraitsofdominantinfluence(evinerandchapin2003;mcgilletal.2006).thisallows predictionstobemadeabouttheoutcomesofecologicalphenomena,suchasinvasion, succession,orcompetition,withsomeconfidencegivenknowledgeofimportantfunctional traitsoftheinvadingorcompetingspecies(westobyandwright2006).forexample, Spartina+alterniflorainvasionintonativePhragmites+australisandScirpus+mariqueter populationsinchinacausedanincreaseinnetprimaryproductionandcandnstorage. 11

29 Thiswas,inpart,theresultofS.+alterniflorahavingalongergrowingseason,denser canopy,andgreaterrootbiomassthaneithernativespecies(liaoetal.2007).inaddition, Lythrum+salicariainvasionofTypha+latifoliastandsinNewYorkresultedinhighersoil organicmatter(om)contentandgreaternmineralizationrates.whilehydrologywasa majorcontrolonntransformations,l.+salicariatotalbiomasswasmorethandoublethatof T.+latifolia,whichincreasedlitterinputsandresultedinhighersoilOMcontent(Fickbohm andzhu2006).ifatraitisfoundtostronglyaffectecosystemprocesses,e.g., decomposition,thenpredictionscanbemadeaboutthemagnitudeofeffectonthatprocess forspeciesthatsharethattrait. Althoughthebenefitsofinvestigatingtheinfluentialfunctionaltraitsaffecting ecosystemprocesseshavebeenmadeclear(diazandcabido2001;lavorelandgarnier 2002;Arndt2006;SchindlerandGessner2009),notallvariationinecosystemfunction, suchascandnmineralization,canbecompletelyexplainedbyafewfunctionaltraits.in somecases,speciesidentityisthebestpredictorofecosystemleveleffects(wardleetal 2003).Therefore,ifpossible,itisimportanttosimplifycomplexplantcommunitydatatoa fewkeytraitsoflargeeffect,aswellastoinvestigateifspecificdominantspeciesare stronglyinfluencingtheoverallecosystemfunction,perhapsbynoveltraitsnotsharedby therestofthecommunity.invasionsbyexoticspeciesareagoodexampleofsituations wherebothapproachesmaybeuseful. Phragmites+australishasbeenshowntoreducetheavailabilityofinorganicNin wetlandsandincreaseorganicnretention(findlayetal.2002)comparedtonative Spartinaspecies,likelyduetodifferencesinlitterchemistry.Orwinetal.(2008) demonstratedthatcsubstrateidentitycaninfluencesoilchemistry,microbialmetabolism, 12

30 andsoilmicrobialcommunitystructure,allofwhichcouldinfluenceecosystemprocesses suchasdecompositionandnpp(througheffectsonplantavailablenutrients).angeloniet al.(2006)showedthatinvasionbytypha+ glaucaintoamichiganmarshincreasedsoil organicmatterandalteredthecompositionofthebacterialandspecificallydenitrifier communities,whichcouldhavebeeninfluencedbythehigherabovegroundbiomassoft. glaucacomparedtotheinvadedcommunity.whileitispossiblethatplantinvasionsin temperatewetlandscouldstimulatetheshort]termuptakeofnthroughincreasedbiomass production,invasivespeciescouldhavedifferentlonger]termimpactsonn transformationsinwetlandsthroughmorecomplexcontrolsonsoilmicroenvironments andsubstratequality. Phragmites+australis(commonreed),Phalaris+arundinacea(reedcanarygrass),and Typha glauca+(hybridcattail)aresomeofthemostsuccessfulinvasivespeciesinnorth Americanwetlands(ZedlerandKercher2004).Phragmites+australisisinvadingwetlands throughouttheunitedstates,andisofparticularconcerninthemidweststatessuchas Michigan(Marksetal.1994).Phragmites+australisisahigh]biomassinvasive(Windham andlathrop1999;minchintonandbertness2003),andcanhavehighnuseefficiencyand lowlitterquality(findlayetal.2002).inmichiganwetlands,p.+australisoccursinthesame wetlandzoneastypha+latifoliaandisstillintheprocessofaggressivelyinvadingintosites whereithascolonized(s.hamilton,personalcommunication).phragmites+australishas beenshowntoreducetheavailabilityofinorganicninwetlands(windham2001)and increasenretention(findlayetal.2002)comparedtospartinaspecies,likelydueto differencesinlitterchemistry.similarcomparisonswithtypha+latifoliahaveyettobe made. 13

31 Phalaris+arundinaceaandT.+ glaucaaresimilartop.+australisinthattheyproduce higherbiomasscomparedtonativespecies,spreadthroughclonalgrowth,anddisplace nativewetlandplantcommunities(lavergneandmolofsky2004;wetzelandvandevalk 1998;Hudon2004).ExoticgenotypesofP.+arundinaceawasintroducedtotheUnited Statesca.1850,thoughnativepopulationsareknowntohaveexistedpriortothat introduction(lavergneandmolofsky2004).invasivegenotypeshavebeenshowntocome primarilyfromeuropeandafterintroductionforforage,bioremediation,anderosion control,invasivegenotypeshybridizedwiththelessaggressivenativegenotypes(lavergne andmolofsky2007).currently,thedistributionofp.+arundinaceaincludesmostofthe northernhalfoftheunitedstates.phalaris+arundinaceaisextremelyphenotypicallyplastic andcanadjustmorphologicallytomatchabioticconditions(martina2006),whichhasbeen assumedtoaiditwheninvadingintonewareas.typha glauca,currentlydistributed acrosstheeasternunitedstates,isahybridbetweent.latifolia(native)andtypha+ angustifolia(exotic)thatisveryaggressiveandcanout]competethenativecattailwhen theyco]occur.typha+angustifoliaisnativetoeuropebutthedateofintroductiontothe UnitedStatesisnotwellknown,thoughitwaslikelyatthebeginningofthe20 th century. Forinvasivespeciesthataremoreproductive(intermsofbiomass)thannatives,such asp.+australis,p.+arundinacea,andt.+ glauca,oneof+twomechanismsmayberesponsible: (1)invasiveshavehighernitrogenuseefficiency(NUE,biomassperunitN)thannativesor (2)theyrespondtonutrientloadingmorethannatives.Whileitiswidelyhypothesized thatthelatteristhecorrectmechanisminmostcircumstances(zedlerandkercher2004; Tyleretal.2007),invasivespeciescanstillinvadewetlandsatlownutrientlevels(Green andgalatowitsch2002)andthereisalsoevidencethatinvasivesaresuccessfulbecauseof 14

32 greaternue(funkandvitousek2007),atleastinlowresourcehabitats.++athorough understandingofhowtheseinvasiveplantsareinfluencingcandncycling,alongwiththe controllingfactors,willhelptopredicttheimpactsofinvasion.whiletherehasbeensome researchontheeffectsofinvasivespeciesinwetlands(e.g.,findlayetal.2002;angeloniet al.2006;liaoetal.2007),fewstudieshavedirectlyinvestigatedthemechanisms responsibleforecosystemprocesschangesduetoinvasionandevenfewerhavelookedat multipleinvasivespeciessimultaneously. Decomposition:AbioticandBioticDeterminants Decompositionisanessentialecosystemprocessdefinedasthephysicalandchemical breakdownoforganicmatter(chapinetal.2002).duringdecomposition,organicmatteris brokendownintoitschemicalcomponentsreleasingco2totheatmosphereandnutrients tothesoil.decompositionconsistsofthreebasicprocesses:leaching,fragmentation,and chemicalalteration(chapinetal.2002).leachingisthemobilizationoflabilesoluble materialsintowater,suchassugarsandaminoacids,fromdecomposingom.inalitterbag fieldincubationinvestigatingthecontrolsondecompositionintwomediterranean ecosystems,itwasfoundthatleachingwasanimportantphaseindecompositionthat lasted2]4months(gallardoandmerino1993).fragmentationisthephysicalbreakdown oflargedetritusmainlybysoilanimals(thoughfreeze]thawandwet]drycyclescanalso fragmentorganicmatter)thatincreasessurfaceareaformicrobialactivityandcanbea veryimportantprocessinenvironmentswheresoilanimalsthrive(verhoefandbrussaard 1990).Soilanimalscanalsoinfluencethemagnitudeanddirectionoftheeffectsoflitter diversityondecomposition(hattenschwilerandgasser2005).chemicalalterationmainly 15

33 occursbytheactionofmicrobialactivitythoughsomealterationcanoccurspontaneously, suchaswhenexposedtouvradiation(austinandballare2010). Microbes(mostlyfungiandbacteria)releaseextracellularenzymesthatreactwith organicmatterresultinginthebreakingofchemicalbonds.ultimately,throughmicrobial respiration,organicmatterisusedasanenergysourceandoxidizedtoco2(inaerobic environments).themajorityofsoilrespirationisduetotheactionofbothbacteriaand fungi,thoughaspectsofhowtheyinfluencedecompositioncandifferinimportantways. Fungiarethemaininitialdecomposersofdeadplantmaterialbecausetheyarecapableof producingenzymesthatcanbreakdownmostplantcompounds,includinglignin(chapin etal.2002).thoughtheyarethedominantdecomposersinecosystemslikeforests becauseoftheirlargenetworksofhyphae,theyarepoordecomposersinlowoxygen environmentslikewetlands.conversely,bacteriacansurviveinoxygenpoorsoils(e.g., wetlands)andareresponsibleforamyriadofchemicaltransformations,suchas nitrification,denitrification,andmethanogenesisthatoccurinlowoxygenconditions, thoughinsoilsthathavedrying]rewettingcycles,bacteriaarenotnearlyasdominant,and insomecasesfungicanbecomedominant(stricklandandrousk2010). Manyfactorsinfluencemicrobialbiomassandactivityandthusdecompositionrates, includingtemperature,moisture,oxygenconcentration,andorganicmatterquality (Wardle1992).Generally,increasingtemperaturecandirectlyenhancedecompositionby promotingmicrobialactivitywithalmostzeromicrobialactivityatverylowtemperatures. Reichsteinetal.(2000)incubatedsubalpinesoilatthreetemperatures(5,15,and25 C) andfoundthatincreasingthetemperatureby10degreesnearlytripledcmineralization rates.whileinmanylaboratoryincubationstheeffectoftemperatureonthe 16

34 mineralizationofsoilorganiccarbonisobvious,astudybygiardinaandryan(2000) compileddatafrom82sitesandfivecontinentsanddeterminedthatdecompositionof organicmatterfoundinforestmineralsoilsisnotcontrolledbytemperaturelimitationsto microbialactivity.thisapparentlackofatemperatureeffectondecompositionmay actuallybeduetomultipleenvironmentalconstraintsoncarbonmineralization,which mightalsobesensitivetoglobalwarming(davidsonandjanssens2005). Soilmoistureisneededduetotherequirementofwaterfornormalbioticactivity, thoughassoilmoistureincreasestofullysaturatedconditions,oxygendiffusionisreduced leadingtoanoxicconditions.oxygenisrequiredforaerobicrespiration,whichyieldsmore energygaincomparedtoanaerobicrespiration.intheabsenceofoxygen,no3 ] isusedas anelectronacceptor(denitrification)followedbymn 4+,Fe 3+,SO4 2],CO2,andfinallyH +, withtheorderdictatedbytheenergyefficiencyofthevariouselectronacceptors(more energyisgainedbyusingno3 ] asanelectronacceptorcomparedtomn 4+ )(Reddyand Delaune2008).Becausemoreenergyisgainedduringaerobicrespirationversus anaerobicrespiration,lowoxygenconcentrationsusuallyresultsinlowdecomposition rates,thoughanaerobicrespirationusingno3 ] canbealmostasefficient.oxygen availabilitycanalsoinfluencehumicacidformation;ramunnietal.(1987)foundthatthe formationofhumicacidsduringdecompositionincreasedinthepresenceofoxygen. Finally,organicmatterqualitycanbeamajorcontrolondecompositionrates. Organicmatterqualityisdependentonitschemicalcomposition,includingsizeof molecules,typeofchemicalbonds,regularityofstructures,toxicity,andnutrient concentration(chapinetal.2002).ligninisveryrecalcitrant(hardtodecompose)because 17

35 itisalargephenoliccompoundwithaveryirregularstructure,makingenzymatic degradationdifficult.consequently,plantmaterialwithhighconcentrationsoflignin decomposesslowerthanmaterialwithlowligninconcentrations(melilloetal.1982). OrganicmatterC:Nratiosorlignin:Nratioshaveanegativerelationshipwith decompositionratesandareregularlyusedasmetricsofsubstratequality(lability)inthe literature.inastudyofsevencanopyspeciesfromasubtropicalevergreenforestinjapan, XuandHirata(2005)founddecompositionrateswerestronglycontrolledbyNandlignin content,aswellasc:nandlignin:nratios.inadifferentstudythatspanned10years,21 sites,andsevenbiomes,partonetal.(2007)foundthatnreleaseduringdecomposition wasmainlycontrolledbyinitialnconcentrations,i.e.,litterwithhighc:nratios(lown content)releasedlessnovertheincubationperiodthanlitterwithlowc:nratios(highn content).theyalsofoundthatnetnreleasestartedwhenlitterc:nratiosfellbelowabout 40(rangeof31]48). Besidesthefourmajordeterminantsofdecompositiondescribedabove,litterdiversity canhaveprofoundeffectsondecompositionrates,thoughtherelationshipbetweenlitter diversityanddecompositioncanbepositive,negative,orneutral(gessneretal.2010). Blairetal.(1990)usedtheleaflitterfromthreecommonwoodyspecies(Acer+rubrum, Cornus+florida,+andQuercus+prinus)totesttheeffectsofsingle]versusmixed]specieslitter bagsondecompositionandfoundthatmixed]specieslitterbagshadgreaterdecomposition ratesthansingle]specieslitterbags,buttheeffectsofthemixed]specieslitterbagscould notbepredictedfromthesingle]specieslitterbags.theyhypothesizedthatthedifference betweenmixed]andsingle]specieslitterdecompositionwasexplainedbychangesinthe decomposercommunity(blairetal.1990).inasimilarexperimentperformedto 18

36 determineifenhanceddecompositionduetoincreasedlitterdiversitywascausedbylitter speciescompositionoralterationtothemicroenvironment,itwasfoundthattherewas moresupportforchangestothemicroenvironment(physicalfactorsanddecomposer community)thanforlitterspeciescomposition(hectoretal.2000).litterdiversityeffects ondecompositionmaybespecificallyimportantinplantinvasionsbecause,initially,the additionofaninvasivespeciesmayincreaselitterdiversity,butlaterintheinvasion,ifthe invasivespeciesformsamonospecificstand,litterdiversitywouldbelower. Wetlandsarehighlyproductiveecosystemsthatundergoperiodicfloodingevents; therefore,productivityisusuallygreaterthandecompositioncausingtheaccumulationof organicmatterinwetlandsoils(mitschandgosselink2000).becauseofthelowoxygen levelsinthesoil,fungiandsoilanimalscannotsurviveandthereforebacteriamediatethe majorityofdecomposition.infloodedsoils,theabsenceofbothfungiandsoilanimals (AndersonandSmith2000)slowsdecompositionduetothepositiveeffectsof fragmentationbysoilanimalsandligninbreakdownbyfungi(hattenschwileretal.2005). Asdiscussedabove,wetlandsareconsideredbiogeochemical hotspots becauseofthe landscapesinknatureofwetlandscombinedwithwettinganddryingevents(mcclainetal. 2003).These hotspots arecreatedbythediversityofredoxreactionsthatoftenoccurin closeproximitytoeachotherduetothemicro]gradientsofoxygenconcentrationsinsoil porespace(burginetal.2011),whichoftenvaryspatiallyandtemporally.thismakes wetlandsthesiteofmultipletransformationpathwaysformanyelements,includingc,n, Fe,P,S,andHg. Wetlandplantscaninfluenceallofthemajordeterminantsofdecompositiondiscussed above,includingtemperature(soilshading;evinerandchapin2003),soilmoisture 19

37 (evapotranspiration;gouldenetal.2007),oxygenavailability(radialoxygenloss;soukup etal.2007)andorganicmatterquality(litterquality;questedetal.2007).therefore,plant communitycompositionisanimportantfactortoconsiderwhenattemptingtounderstand elementalcyclinginwetlands.additionally,plantscan condition soilbyinfluencingthe soilmicrobialcommunity,soilnutrientavailability,primingeffect(fontaineetal.2003),or byalloftheaboveeffects.thisconditioningcanthenfeedbacktoalterthedecomposition ofplantominputs,suchaslitter.the home]fieldadvantage phenomenon,describedby Gholzetal.(2000)andAyresetal.(2009),isanexampleofsoilconditioningwheresoil microbesbecomeaccustomedtoominputsbythedominantplantspecies,resultinginthe OMinputsfromthatplantspeciesdecomposingfaster(Stricklandetal.2009).Amore completeunderstandingofplanteffectsoncandncyclinginwetlandsisrequiredtobe abletopredicttheeffectsofplantinvasiononbiogeochemicalcycling. ResearchObjectives Thebroadgoalofmydissertationresearchwastoquantifytheecosystem consequencesofinvasiveplantspeciesintemperatewetlands,focusingonphragmites+ australis,+phalaris+arundinacea,andtypha+ glauca.thefirstpartofmyresearch(chapter 2)characterizesthespatialvariabilityinCandNstorageandorganicmatterqualityin24 wetlandsinsouth]centralmichigan.inchapter3,iinvestigatethemechanismsbywhichp.+ australisinfluencescandncyclinginthreewetlandsincentralmichigan.inchapter4,to understandtheeffectsoflitterquality,soilorigin,andplantdiversityoncandn mineralization,iperformedtwolaboratoryincubationsusinglitterandsoilcollectedfrom monospecificstandsofinvasivespecies.together,theseapproachesallowedmetotestthe 20

38 followinghypothesesregardingdirectandindirecteffectsofinvasiveplantsonplant communitycompositionandecosystemprocessesinwetlands: + Hypothesis+1+(Chapter2):Invasionintowetlandsbyplantspeciesthattypicallyform monospecficstandsreducespeciesrichnessandevenness,andthereforetherewillbea negativerelationshipbetweentheinvasivespeciesdominanceandshannondiversity. + Hypothesis+2+(Chapter2):Invasiveplantshavehighernitrogen]useefficiency(NUE) thannatives,leadingtohigherbiomassperunitofavailablenaswellaslowerncontentof biomassandlitter(figure1]1;pathway1,10). + Hypothesis+3+(Chapter2):Thelowerquality(lowerNcontent,higherC:Nratio)oflitter fromtheinvasivespeciesresultsinlowerratesofdecomposition,increasingratesof organicmatterstorageininvadedwetlands(figure1]1;pathway8,9). Hypothesis+4(Chapter2and4):VariationamonginvasivespecieseffectsonCandN mineralizationratescanbeattributedtodifferencesinplanttraitsamongspecies, specificallylitterquality(figure1]1;pathway3,8,9). + Hypothesis+5(Chapter3):Invasiveplants(specifically,Phragmites+australis)influence CandNcyclingdirectlybyaffectingplantNuptake(Figure1]1;pathways1,4and1,5,9) andindirectlybyaffectingsoilclimate(figure1]1;pathways2,6,9and3,7,6,9)andthe qualityandquantityoforganicmatterinputs(figure1]1;pathway3,8,9). 21

39 Hypothesis6(Chapter4):CandNmineralizationratesdependnotonlyonthespecies] specificqualityofthelitter(hypothesis4),butalsoontheconditioningofthesoilbythe dominantspecies.thesoilconditioningeffectcanbeduetotheprimingeffect(figure1]1; pathway3,8,9),differencesinsoilmicrobialcommunity(figure1]1;pathway9),orsoil nutrientavailability(figure1]1;pathways1,5,9and8,9). + Hypothesis+7+(Chapter4):Mixturesoflitterfromdifferentplantspecieshavehigher decompositionratescomparedtolitterfrommonospecificstandsduetohighersubstrate diversity(fig.1]1;pathway3,8,9).hence,invasivespeciesdecreasedecompositionrates byreducingspecies(andhencelitter)diversity. 22

40 Alters PCC, including dominance Plant Community Composition (PCC) Invasive Species Introduction Nitrogen Use Efficiency/ Productivity Plant N Uptake N Retention 4 C and N Storage and Cycling Introduced plant traits 3 1 Litter N concentration 10 Plant Traits Leaf Area Index/ Biomass Production N substrate available for microbes 5 Soil Microenvironment 9 2 C and N cycling rates Determines plant trait composition and dominance Soil temperature Litter Inputs Soil Shading Microbial Community/ Metabolism Substrate Quality, Quantity and Diversity Amount, quality and diversity of OM available for decomposition Figure 1-1. Interactions between plant community composition (PCC), plant traits and soil microenvironment influence ecosystem processes. Plant community composition effects on C and N cycling are mediated though plant traits directly (plant N uptake) and indirectly (substrate quality and soil microenvironment alteration). Invasive species introduce novel plant traits into a community and potentially can alter ecosystem function. Arrows represent pathways of influence and are addressed in the text Pathway Effects Direct Indirect 23

41 Chapter(2( Organic(Matter(Accumulation(and(Quality(in(Michigan(Wetlands:(Consequences(of( Invasive(Plants( Brief(Rationale( Wetlandsprovideanumberofvaluableecosystemservices,suchaswildlifehabitat, floodcontrol,shorelinestabilization,andcandnretentionandstorage(zedler2003). TherehasbeenincreasinginterestinunderstandingthespatialandtemporalpatternofC dynamicsindifferentecosystemsduetotheconcernofincreasinggreenhousegas(co2and CH4)concentrationsintheatmosphere(Smithetal.2012).Globally,wetlandsonlycover 2J6%ofthelandarea,butstore14.5%oftheterrestrialCstocks(Postetal.1982)mostly duetotheirhighproductivityandlowdecompositionratescausedbyprominentanaerobic conditions(reddyanddelaune2008).whilemostoftheglobalwetlandcstocksare associatedwithpeatlandsinnorthernlatitudes(roulet2000),temperatewetlandscanalso beimportantlandscapesinksforbothcandn(eulissetal.2006).therolewetlandsplay innretentionhasbeenknownforawhile,thoughtheexactmechanismsandprocesses associatedwithncyclinginwetlandsisstillanactiveareaofstudy(chapmanetal.2006). Wetlandsareknownasbiogeochemical hotspots becauseoftheallochthonousinputsof carbonsubstratesandnutrients,alongwithafluctuatinghydrologycausingtemporal variationtotheredoxstatusofthesediment,whichcreatestheidealenvironmentforn processessuchasdenitrification(mcclainetal.2003).wetlandsarethereforeknownto bothstorenandlosenthroughdenitrification. Forsomeofthesamereasonsthatmakewetlandsbiogeochemicalhotspots, wetlandsalsocanbeoneofthemostinvadedecosystems,giventhattheyserveassinksfor invasivespeciespropagules(carriedbyinflowsofsurfacewater),nutrients,and 24

42 disturbance(zedlerandkercher2004).disturbance(eschtruthandbattles2009), propragulepressure(lockwoodetal.2005),andnutrientenrichment(davisetal.2000) haveallbeenshowntoincreasethecolonizationandestablishmentofinvasivespecies, makingwetlandsverysusceptibletoinvasion.additionally,manyofthespeciesthat invadewetlandsareclonalspeciesthatcanformmonospecificstands,whichreduces diversityandspeciesinteractions.invasivespeciesintemperatewetlandsareusuallyhigh biomassproducersassociatedwiththicklitterlayers.becausethesespeciesusually producemorebiomassthannativespecies,theyeitherhavehighernitrogenuse efficiencies(nue:theamountofbiomassproducedperunitn)orareabletoaccessa largerpoolofncomparedtonatives.organicmatterbuildupbeneathmonospecificstands ofaggressivewetlandinvaders,suchastypha glauca,hasbeendocumented(ehrenfeld 2003;Angelonietal.2006),thoughthepatternacrossdifferentwetlandtypeshasnotbeen evaluated.withtheprevalenceofinvasionintemperatewetlandsitisimportantto understandtheeffectofinvasiononwetlandprocessessuchascandnstorageandorganic matterquality.itispossiblethatinvasionbyhighbiomassinvasivespeciescouldincrease wetlandcandnstorageand,therefore,couldbeapositiveoutcomeofinvasion. ( Whiletherehasbeensomeresearchontheeffectsofinvasivespeciesinwetlands (e.g.,findlayetal.2002;angelonietal.2006;liaoetal.2007),fewstudieshavedirectly characterizedthespatialvariabilityincandnstorageandorganicmatterqualityandeven fewerhavelookedatmultipleinvasivespeciessimultaneously.additionally,thoughthese specieslikelyhavecumulativeeffects,theycanalsodifferinplanttraits,e.g.,litterquality, andthereforeitisimportanttounderstandthedifferencesamonginvasivespecies.the broadgoalofthischapteristoquantifytheconsequencesofinvasivespeciesintemperate 25

43 wetlandsoncandnstorageandorganicmatterquality.inthefirstpartofthischapter,i quantifiedtheeffectsofinvasivespeciesonplantcommunitycomposition,litterandsoilc andnstocks,andomquality.inthesecondpartofthischapter,iusedtwosoilassaysto determinedifferencesincandnmineralizationratesfromsoilcollectedfrom monospecificstandsofthemostdominantinvasivespecies. * Objectives,(Hypotheses,(and(Predictions( Objective)1:Todeterminethecumulativeeffectofinvasivewetlandplantsonspecies diversity,candnstorage,andorganicmatterquality. Hypothesis)1:Invasionintowetlandsbyspeciesthatcanformmonospecficstandsreduces speciesrichnessandevenness. ) Prediction1.1:Therewillbeanegativerelationshipbetweeninvasivespecies dominanceandshannondiversity. Hypothesis)2:InvasiveplantspecieshavehighernitrogenJuseefficiency(NUE)thannative species,leadingtolowerncontentoftheirbiomassandlitter. Prediction2.1:Therewillbeapositivecorrelationbetweenthedegreeofinvasion (totalbiomassofinvasivespecies)andtheoverallplantcommunitynue. Prediction2.2:Degreeofinvasionwillbepositivelycorrelatedwithorganicmatter C:Nratios(litterandsoil). 26

44 * Hypothesis)3:InvasiveplantspecieshavelitterwithhigherC:Nratiosthannativespecies litter,leadingtoincreasedorganicmatterstoragefromslowerratesofdecomposition. Prediction3.1:Therewillbeapositivecorrelationbetweenthedegreeofinvasion andlittercandnstocks,soilcandnstocks,andtotalecosystemcandnstocks. Prediction3.2:BasedonhypothesizedhigherNUEofinvasives,litter,soil,and ecosystemnstockscouldeitherdecreaseorincreasewiththedegreeoninvasion. ThereisuncertaintybecausewhiletheoveralldecreaseintissueNcontentshould decreasenstocks,thedecreasedncontentcouldalsolowerthequalityoftheom andthereforeleadtolowdecompositionratesandnbuildup. Objective)2:Forobjective1,ItestedthecumulativeeffectsinvasivespecieshaveonCand NstocksandOMquality,thoughtherewasevidenceforvariationamonginvasivespecies inkeyplanttraitsthatcouldinfluencethespeciesjspecificmagnitudeofeffect.this variationwasexaminedthroughtheuseoftwoassaystodeterminedifferencesincandn mineralizationratesfromsoilcollectedfrommonospecificstandsofthemostdominant invasivespecies.anadditionalobjectivewastobeabletolinkthevariationamong invasivespeciestoplanttraits,suchaslitterquality. Hypothesis)4:Thequality(C:Nratio)ofsoilcollectedwithinmonospecificstandsofthe mostdominantinvasivespeciesfromthewetlandsurveywillinfluencecandn 27

45 mineralizationrates,andthevariationinsoilqualitywillmainlybeduetolitterquality differencesamongspecies. Prediction4.1:ThewillbeanegativerelationshipbetweensoilC:NratiosandCand Nmineralizationrates. Prediction4.2:Soilcollectedfrommonospecificstandsofthespecieswiththemost recalcitrantlitter(highc:nratios)willhavethehighestsoilc:nratios,and thereforethelowestmineralizationrates. ( Methods( Study*sites*and*sampling*for*wetland*survey* ThisstudywasconductedneartheW.K.KelloggBiologicalStation(KBS)on MichiganStateUniversitypropertyinsouthwesternMichigan,andatLakeLansingPark (LLP)incentralMichiganduringpeakbiomassgrowth(lateJunetoearlyAugust).The regionaroundkbsliesonaglaciallandscapeandhasabundantwetlandcover(approx. 10%),withlowlevelsofresidentialdevelopmentinalandscapedominatedbyforests,rowJ cropagriculturalfields,andabandonedfields.thewetlandsoflakelansingparkare embeddedinamosaicofwoodlotsandresidentialareasandarecontiguouswiththelake system. Inthesummerof2007,23wetlandsnearKBSandonewetlandatLLPweresampled (forgpscoordinatesofeachsiteseetable2j1).wetlandsamplingsiteswerechosento spanthediversityofwetlandsaroundkbsthatsupportemergentvegetationincludingthe 28

46 focalinvasivespecies,alongwithanadditionaldepressionalwetlandatllpdominatedby Phragmites*australis.Wetlandswereclassifiedbasedontheirhydrogeomorphicsettingas wellasthedominantwatersource,estimatedusingdissolvedmagnesium(mg 2+ )inthe wetlandsurfacewaterasanindicatorofprecipitationversusgroundwaterdominance; highermg 2+ concentrationsindicatedhighergroundwatercontributiontostandingwater (Stauffer1985,WhitmireandHamilton2008).Categoriesincludedepressional (precipitationdominated),intermediate(inbetweengroundwaterandprecipitation dominance),groundwaterdominated,andlakeside.lakesidewetlandsweregivena uniqueclassificationduetotheoverridingeffectanadjacentlakehasonthephysicaland chemicalwetlandenvironment(hgmclassification;brinson1993).thesewetlandswere relativelysmall,usuallywithatotalsurfaceareaoflessthanonehectare.themajorityof thestudysiteshadrelativelypurestandsofp.*australis,*phalaris*arundinacea,and*typha* spp.(hereafterphragmites,phalaris,typha,respectively),ormixturesofrelativelypure standsofthesespecies.themostcommonnative,nonjinvasivegraminoidspeciesatthese sitesincludedsedges(carexspp.),rushes(juncusspp.),andspikejrushes(eleocharisspp.). Othercommonwetlandspeciesfoundatthesesitesincludedbuttonbush(Cephalanthus* occidentalis),pickerelweed(pontederia*cordata),spatterdock(nuphar*advena),and smartweed(polygonumspp.). Arandomlyplacedlineartransectwassetupintheemergentvegetationzoneat eachsite.six1.0x0.5m(0.5m 2 )quadratswereestablishedalongeachtransectfor vegetation,litter,andsoilsampling.thequadratswererandomlyplaced(1j10mdistance betweenquadrats)alongthetransectusingarandomnumbertable.ineachquadrat,all 29

47 plantspeciesthathaddevelopedpasttheseedlingstagewereidentifiedandpercentcover wasestimatedforeach.speciesjspecificabovegroundbiomasswasclippedatthesoil surface,driedat65 Cfor48hours,andweighedonatopJloadingbalance.Litterdepthwas measuredandaknownareaoflitter(629cm 2 )wasremovedfromthesoilsurface, avoidingmostlydecomposedmaterialbeneaththerelativelyfreshlitterlayer.litter sampleswerecollected,dried,andweighedinthesamemannerasbiomasssamples. Surfacesoilwassampledto10cmdepthusingasoilcorer(246cm 3 )andsampleswere transportedtothelaboniceandfrozenuntilprocessed.forprocessing,soilswerethawed, sieved(4mm),subjsampledforbulkdensityandgravimetricwatercontent(gwc) determination,andthendriedtoaconstantmassat80 C. Carbon*and*nitrogen*analysis* Driedabovegroundbiomassandlittersamplesweregroundandhomogenizedusing acyclonesamplemill(udycorporation,fortcollins,co)anddriedsoilsampleswere groundusingamortarandpestle.percentcandnweremeasuredforaboveground biomass,litter,andsoilusingacostechelementalcombustionsystem4010(costech AnalyticalTechnologiesInc.).Sampleswereruninduplicatewithatropineusedasa standardevery10samples.subsamplesofdrysoilfromallsitesweretestedforcarbonate mineralsandconcentrationswerefoundtobenegligible.abovegroundbiomasscandn stockswerecalculatedbymultiplyingeachspecies tissue%cand%nbyitstotaldry biomassandthensummingspeciesjspecificcandnstocksforeachquadrat.litterandsoil CandNstockswerecalculatedbymultiplying%Cor%Nbytotallittermass.SoilCandN 30

48 stockswerecalculatedfromsoil%cor%n,soilbulkdensity,andsamplingdepth.totalc andnecosystemstockswerecalculatedbysummingsoil,litter,andbiomassstocksfor eachsite.carbontonitrogenratioswereusedasameasureoforganicmatter(om)quality. LowC:NratiosindicatehighqualityOMandhighC:NratiosindicaterecalcitrantOM. Plantabovegroundtissue%NwasusedtodetermineplantJandplotJlevelnitrogen useefficiencies(nue).nuewasdefinedastheamountofbiomassproducedperunitn (vanruijuenandberendse2005)andwascalculatedontheplotlevelbyfirstdetermining thenueforeachspeciesineachplot(totalbiomassdividedbythetissuencontent). Thoughsimilar,NUEisnotperfectlyscaledwithbiomassC:Nratiobecause%Cvaried amongspecies(~40to50%c),and,therefore,bothcanbeinformative.thisisan acceptablewaytocalculatenueinthisstudybecauseallspecieswerecollectedatpeak biomassandwereeitherannualorperennialdeciduousgrowthforms,inwhichallbiomass wasproducedduringasinglegrowingseason.forbuttonbush(woodyhabit),theonly abundantspecieswithperennialabovegroundbiomass,leaves,andstemswereseparated andannueestimatewasmadeusingleaftissue.aweightednueaveragewasthen calculatedforeachplotandaveragedforeachsite(hereaftercalledthesitenue). Estimation*of*plant*abundance* Percentcoverwasestimatedforeveryplantspeciesineachofthesix0.5m 2 quadratsateachsite.thispercentcoverwasthenassignedtoacoverclassfrom1to6(1: 0J5%cover;2:6J25%;3:26J50%;4:51J75%;5:76J95%;6:96J100%).Shannon s diversityindexwascalculatedusingpercentcoverdatafollowingseefeldtandmccoy (2003)andwasusedasameasureofbiodiversity(incorporatingbothspeciesrichnessand 31

49 evenness).thepercentofthetotalbiomassfrominvasivespecies(referredtohereafteras invasivespeciesdominance),whichincludedthecombinedbiomassofphragmites, Phalaris,andTypha,wascalculatedbydividingtheircombinedbiomassbythetotal biomassineachquadrat.nativespeciesdominancewascalculatedsimilarly(totalnative speciesbiomassdividedbytotalbiomass)withnonjnative,nonjinvasivespeciesexcluded frombothmetrics.phalaris%biomasswascalculatedbydividingphalarisbiomassina quadratbytotalbiomassinthatquadrat.insomecases(seestatisticalanalysissection) Phalaris*wasanalyzedinsteadoftheinvasivespeciescategoryduetoitspresenceatthe majorityofsitessampled(table2j1). Soil*carbon*quality*assay Todeterminedominantspecieseffectsonorganicmatterquality(asaerobicC mineralizationrates)inthesewetlands,alaboratoryincubationwasdoneattwo temperatures(7 Cand23 C)usingsoilscollectedundermonospecificstands(>90% cover)ofthethreemostdominantspeciessampledduringthesurveystudy.monospecific standswereusedbecausespecieseffectsonsoilcqualityaremorelikelytobedetected whenonlyonespeciesispresent.thetwotemperaturesusedrepresentgrowingseason averagetemperature(~23 C)andnonJgrowingseasonaveragetemperature(~7 C)for southernmichigan.soilswereincubatedattwotemperaturessotheq10foreachspeciesj specificsoilcouldbecalculated.thetemperaturecoefficient,q10,isametricthat describestherateofchangeinabiologicalorchemicalsystemwithanincreaseof10 C. ThisallowedacomparisontobemadeoftemperatureeffectsonCmineralizationratesdue 32

50 todominantspecies.q10wascalculatedwiththefollowingequation:q10= (R2/R1)^10/(T2JT1),whereR1istheCmineralizationrateatlowtemperature,R2istheC mineralizationrateathightemperature,t1isthelowtemperatureandt2isthehigh temperatureindegreescelsius(solondzetal.2008). Elevenwetlandsitesweresampledfortheincubations:4Typha*dominated,4 Phalarisdominated,2Phragmitesdominatedand1Carex*lacustrisdominated.Forasiteto beconsidereddominatedbyaspecificspecies,thatspecieshadtoconsistof>90%ofthe totalbiomass.becausetheaggressivegenotypeofphragmitesisarecentinvadertoinland Michigan(Hamilton,personalcommunication),onlytwositesfromthe24thatwere surveyedcouldbeclassifiedasamonospecificstand.additionally,duetolownative speciesabundance,onlyonec.*lacustrisdominatedareawasincludedinthisincubation. Becauseoftheabsenceofreplicationatthesitelevel,C.*lacustriswasleftoutofstatistical analysesbutisplacedinsomefiguresasanativereference.soilsampleswerecollectedin February2007attheendofthegrowingseason.Fivesoilcores(5cmdepth)were collectedateachsiteusingalineartransectsimilartothedesigndescribedabove(11sites x5cores=55cores).thesesoilcoresweresealedinwhirljpakplasticbags(nasco), immediatelyplacedonice,andtransportedtothelaboratorywheretheywerekeptfrozen (J20 C)untilthestartoftheincubation.* Priortothestartoftheincubation,soilswerethawedatroomtemperaturefor24 hoursandhandsievedtoremoverocksandlargeroots.eachsoilcorewasthensubj sampledforbulkdensityandgwcdetermination.thedrymassofthesubjsamplewas measuredbyovendryingat80 Cfor48hours.Drymassvalueswereusedinbulkdensity 33

51 andgwccalculations.driedsoilswerethengroundandhomogenizedusingamortaland pestleandrunonanelementalcombustionsystem(costechecs4010,valencia,ca)for %Cand%Nanalysis.Sampleswereruninduplicatewithatropineusedasastandard every10samples.theremainingwetsoilwasthensplitinto2subsamplesof approximately10gandplacedintoa250mlincubationjar(chromatographicspecialties, Inc.;Ontario,Canada).Theseincubationsampleswereequilibratedfor7daysat4 Cto allowthecmineralizationpulsefromrootdeathtopass(weintraubandschimel2003). Duplicatejarswerethenrandomlyassignedatemperaturetreatment,flushedwith ambientair(~400ppmvco2),andlooselysealedwithlidsfittedwithseptatoallowroom airtoenterthejaruntilthestartofaco2extractionround(seebelow).thetwo temperaturetreatmentsconsistedofhightemperature(roomtemperature,~23 C)and lowtemperature(coldroom,~7 C).Alljars(110total;4vegetationclassesx1,2,or4 replicatesitesx5replicatecorespersitex2temperatures)wereincubatedinthedarkfor 36days.Similarsoilmoistureconditionswerecreatedacrossallincubationsamplesby bringingeachtoacomparablemoisturecontentusingdistilledwaterbeforethebeginning oftheexperiment(40j60%representingidealnonjlimitingconditions).moisturecontent wasmaintainedweeklyoverthecourseoftheincubationbyaddinganappropriatevolume ofdistilledwateraftereachjarwasweighedtodeterminewaterloss.* Carbonmineralizationrateswereestimatedforsix24Jhourperiodsoverthe36Jday experiment,ondays1,3,8,15,22,and36.duringeachperiod,a10mlheadspacegas samplewastakenfromeachjarimmediatelyafterjarsweresealed(time=0)usingathreej waystopcockjfittedsyringe,andthenevery12hoursoverthe24hourperiod,exceptfor 34

52 thefirstround,whichwas48hours.beforegassampleswereextracted,eachjarwas shakenbyhandtomixsoilporespacesandtoreleasetrappedgasbubbles.after headspacesampleswerecollected,jarswereinjectedwith10mlofn2gastoensure constantairpressureandvolume.aftereachround,lidswereremoved,sampleswere gentlyflushedwithambientair,andjarswerewrappedwithplasticwraptoprevent moistureloss. Each10mLheadspacesamplewasanalyzedforCO2partialpressurebyinjecting5 mlofsampleintoappjsystemegmj4infraredgasanalyzer(irga).theirgawas standardizedusingaco2standardgasafterevery10injections.carbondioxide concentrationswerecorrectedforheadspacedilutioncausedbytheaddedn2gas.the slopeofco2concentrationsovertheincubationperiodwasusedtocalculateoverallc mineralizationrates.theseoverallmineralizationratesweredividedbysoildryweight (g)toreportdataonamassbasis(umolco2g J1 day J1 )andbytotalsoilc(sc)toreport dataonascbasis(umolco2g J1 SCday J1 ).SlopeswerediscardedifR 2 valueswereless than0.75,whichcomprisedlessthan2%oftheslopes. N*mineralization*and*nitrification*assay* TodetermineratesofnetNmineralizationandnitrificationinthesewetlands,an aerobiclaboratoryincubationwasconductedusingsoilscollectedundermonospecific stands(>90%cover)ofphragmites,phalaris,andtypha.eightwetlandsiteswereusedin all:3typha*dominated,3phalarisdominated,and2phragmitesdominated,andwerea 35

53 subsetofthewetlandsusedforthecqualityincubation.soilsampleswerecollectedatthe endofthe2008growingseason.threesoilcores(10cmdepth)werecollectedateachsite frompermanentplotsthatwereestablishedduringthesummerof2008aspartofalarger researchproject(8sitesx3cores=24cores).thesesoilcoresweresealedinwhirljpaks (Nasco,FortAtkinson,WI),immediatelyplacedonice,andtransportedtothelaboratory wheretheywerekeptat4 Cfor2daysuntilthestartoftheincubationtoreducemicrobial activity.* SoilsamplesforassaysofNmineralizationandnitrificationwereprocessed similarlytothecmineralizationsoilsamples.aftersieving,10gsubjsamplesweretaken fromtheremainingwetsoil:onesubjsamplewasusedtodetermineinitialno3 J andnh4 + concentrationsbythekclextractionmethod(robertson1999),whiletheotherwasplaced ina100mlplasticcontainer.after30daysofaerobicincubationatroomtemperature,the KClextractionmethodwasusedtodeterminefinalNO3 J andnh4 + concentrations.all extractswereanalyzedbythemicroplatemethodfornitrateandammoniumusing protocolsdevelopedbydr.davidrothstein(dept.offorestry,msu).netratesofn mineralizationandnitrificationwerecalculatedfromthechangesininorganicn(nh4 + + NO3 J )orno3 J,respectively,duringtheincubationperiod(initial finalpoolsizes).similar soilmoistureconditionswerecreatedacrossallincubationsamplesbythesamemethod usedinthecqualityincubation.nmineralizationandnitrificationrateswerecalculatedon asoilmassandsoilcarbonbasissimilartothecqualityincubation. * 36

54 Statistical*analyses* Wetlandsurvey( BecausethemajorityofwetlandssampledwereinvadedbyPhalaris,Phragmites, and/ortypha(23outof24;table2j1)simplelinearregression(slr)analysiswasusedto determinetherelationshipbetweensiteshannondiversityindexandinvasivespecies dominance(%biomassoftotalcommunitybiomass)(hypothesis1).toaddresshypothesis 2,anotherSLRwasperformedtodeterminetherelationshipbetweenvegetationNUEand invasivespeciesdominance.forshannondiversityandnueslrs,all24wetlandswere included;fortheotheranalysesonly20wetlandswereusedduetoincompletedatasets from4wetlands. Toaddresshypothesis3,generallinearmodelswereconstructedtodeterminethe controllingfactorsforbiomass,litter,soil,andtotalecosystemcandnstocks.toexplore speciescontrolsonbiomasscandnstocks,iconstructedgenerallinearmodelsusing speciescompositiondata(invasivespeciesandnativespeciesdominanceorbiomass)as predictorvariables.invasiveandnativespeciesdominance(percentofplantcommunity) wasusedinsteadofinvasiveandnativebiomassforbiomasscstocksbecausethereisan allometricrelationshipbetweenbiomasscandtotalbiomass,thereforethesevariables wouldbeautojcorrelated.thisallometricrelationshipdoesnotnecessarilyexistfor biomassnstockbecausespecies NUEcaninfluencetheamountofbiomass%Npresent. ForthisreasoninvasivespeciesbiomasswasusedtopredictbiomassNstocks.ForlitterC andnstocks,speciescompositiondataandabovegroundbiomasschemistry(%c,%n,and C:Nratio)wereusedaspredictorvariables.Afternosignificancewasfoundforanyplant communitypredictorvariable,phalarisabundancewasincludedasapredictorvariablein 37

55 placeofinvasivespeciesdominanceduetoitspresenceatmostsites(table2j1).to determinespecieseffectsonsoilcandnstocksandsoilc:nratios,generallinearmodels wereconstructedthatincludedplantcommunitycomposition,litterchemistry(%n,%c, andc:nratio),andlitterquantity(massandbulkdensity)aspredictorvariables.finally, fortotalecosystemcandnstocks,generallinearmodelswereconstructedusingplant communitydataaspredictorvariables.nolowerlevelcategories(soil,litter,orbiomass characteristics)couldbeincludedaspredictorsbecausethosedatawereusedtocalculate relatedstocks,andthuswouldbeautojcorrelatedwithtotalecosystemstocks. Forallgenerallinearmodels,siteIDwasincludedinthemodelasarandomfactor, treatingthedesignasnested(quadratsnestedwithinsite).modelselectionprocedures basedonakaike sinformationcriterion(aic)valueswereusedfollowingzuuretal. (2009).Briefly,themostcomplexbiologicallymeaningfulmodel(i.e.,themostcomplex modelconstructedfromnonjautocorrelatedtermsthathypotheticallycouldinfluencethe predictorvariable)wascomparedtomodelsofdecreasingcomplexitybasedonindividual modelaicvalues.thebestjfitmodelwastheonewiththelowestaicvalueandhighest Akaikeweights(wi),whichdescribetheweightofevidenceforonemodelcomparedtothe othermodels.oncethebestmodelwasselectedattable(rcode)dataframewas constructedtodetermineindividualvariablesignificance.hereimainlyreportresultsfor thefinal bestjfit model.fullmodelselectionresultscanbefoundinappendixa. Wetlandclassification(seeabove)wasalsoincludedasapredictorvariabletothebestJfit modeldetermineifitsinclusionwouldimprovethefitofthemodel,thereforeminimizing thepossibleconfoundingeffectofwetlandclassoncandnstocks(forinstance,if depressionalwetlandshavehighomaccumulationindependentofplantcommunity,but 38

56 alsowerehighlyinvaded).inallcasesaddingwetlandclassificationimprovedthefitofthe model(i.e.,itloweredthemodelaic),butinnocasewaswetlandclassificationsignificant andisthereforeleftoutoftheresultssection.modeldiagnosticswereassessedforthe bestjfitmodeltodetermineiftheresidualswerenormallydistributedanddisplayed constanterrorvariances.logtransformationswereusedtocorrectforany heteroscedasticity.allstatisticaltestswereperformedinr(version2.11.1,2010). AssaysofCqualityandNtransformations ThegeneralgoalsforthestatisticalanalysisoftheCqualityassaysweretwofold:(1) todeterminetreatment(vegetationtypeandtemperature)effectsoncmineralization ratesand(2)toexploretherelationshipsbetweencmineralizationandorganicmatter quality(c:nratio)(hypothesis4).toinvestigatetreatmenteffectsoncmineralization rates,iusedarepeatedmeasuresanalysisofvariance(anova)andtukey shsdmultiple comparisontestswereusedtodeterminevegetationandtemperatureeffects,aswellas theirinteractiononcmineralizationrates.fortheanova,soilcoreidwasnestedwithin siteandincludedasarandomeffect.iusedlinearregressionmodelstoexaminetheeffects ofsoilc:nratiosoncmineralizationrates.specieseffectsonq10values,litterandsoil%c, %N,andC:NratiosandNtransformationratesweredeterminedusinggenerallinear models.allstatisticaltestswereperformedinr(version2.11.1,2010). ( ( ( 39

57 ( Table2J1.GPScoordinatesofthe24surveysiteswiththeirhydrologicalclassification, whichisbasedonmagnesiumconcentrations(seemethodsformoredetails),andthe presenceorabsenceofthemostdominantinvasivespecies.phalaris=phalaris* arundinacea,typha=typhaxglauca,phragmites=phragmites*australis. Site Classification Phalaris* Typha* Phragmites* GPSCoordinates LLP precipitation X N, W LS precipitation X N, W LTER precipitation X N, W NLCL lake X X N, W NLCLP lake X X N, W P1 precipitation X N, W P11 precipitation X N, W P18 intermediate X X N, W P26N intermediate X X N, W P26S intermediate X X N, W P3 precipitation X N, W P5 intermediate X N, W P8 intermediate X N, W P9 precipitation X N, W Parker lake X N, W SMCL lake X X N, W SP7 intermediate X X N, W SWMCL lake X N, W SWP7 intermediate X X N, W TM groundwater X N, W TM2 groundwater X X N, W WMCL lake X N, W EF1 lake X N, W LOP groundwater N, W ( ( ( ( ( ( ( 40

58 Results( Wetland*survey TwentyJthreeofthe24wetlandssurveyedwereinvadedbyatleastoneofthethree focalinvasivespecies(phragmites,phalaris,andtypha).asinvasivespeciesdominance increased,shannondiversitydecreased(figure2j1;adjustedr 2 =0.75,p<0.001).A marginallysignificantpositiverelationshipwasfoundbetweensitenutrientuseefficiency (NUE)andinvasivespeciesbiomass(Figure2J2;adjustedR 2 =0.10,p=0.08),thoughthis relationshipwasmainlyduetoonesite,whichwasamonospecificstandofphragmitesthat producedalotofbiomassandhadahighnue.afterexcludingthissite,therewasno relationshipbetweennueandinvasivespeciesbiomass.additionally,therewasa significantpositiverelationshipbetweentotalbiomassandinvasivespeciesbiomass (Figure2J3;adjustedR 2 =0.61,p<0.001). Themodelthatincludedbothinvasivespeciesandnativespeciesdominancewas thebestforpredictingbiomasscstock(table2j2).thismodelhadanakaikeweight(wi) of1.00,givingstrongsupportforthismodel,whiletherewaslittlesupportforthenull model(interceptonly)(wi<0.001).bothinvasiveandnativespeciesbiomasshada positiveeffectonbiomasscstocks,thoughneitherwassignificant.forbiomassnstock, themodelcontainingonlytotalbiomasswasthebestfit(wi=0.99).inthismodel,total biomasshadasignificantpositiverelationshipwithbiomassnstock(table2j2),and similartobiomasscstock,thenullmodelhadverylittleexplanatorypower(wi<0.001). 41

59 ThemostparsimoniousmodelforlitterCstockcontainedbiomass%C,%N,andC:N ratioaspredictorvariables(table2j3;wi=0.48).themodelcontainingphalaris* arundinaceabiomassandbiomass%c,%n,andc:nratiohadanakaikeweightof0.29and a AICvalueoflessthan2,givingsupportforbothmodels,thoughthereismoresupport forthemodelthatexcludedp.*arundinaceabiomass(basedonahigherakaikeweight).in thebestjfitmodel,biomass%nandc:nratiohadapositiveeffectonlittercstock,while biomass%chadanegativeeffect,thoughnovariableinthebestjfitmodelwassignificant (Table2J3).Therewaslittlesupportforanyofthecandidatemodelshavingagreaterfit thanthenullmodelforlitternstock.thebestjfitmodelcontainedbiomass%n(table2j3; wi=0.61)butwaslessthan2 AICfromthenullmodel,givinglittleevidenceforthismodel fittingthedatainameaningfulway.inthebestjfitmodel,biomass%nhadapositiveeffect onlitternstocks.themostparsimoniousmodelforpredictinglitterc:nratioscontained invasivespeciesbiomassandbiomass%n(table2j3;wi=0.45).inthebestjfitmodel, biomass%nhadasignificantnegativerelationshipwithlitterc:nratios(figure2j4), meaningthatasbiomass%nincreased,litterc:nratiodecreased,showingthetightlink betweenstandingbiomassnutrientconcentrationsandlitterquality.invasivespecies biomasshadapositiverelationshipwithlitterc:nratio,thoughthisrelationshipwasnot significant. ForsoilCstock,thefullmodel,whichincludedinvasivebiomass,nativebiomass, littermass,litter%cand%n,andc:nratio(table2j4;wi=0.68),wasmorethanthree timesmoreplausiblethanthenextbestapproximatingmodel.inthefullmodel,invasive speciesbiomasshadasignificantpositiverelationshipandwithsoilcstocks(figure2j5). 42

60 Also,littermasshadamarginallysignificantnegativerelationshipwithsoilCstock.Inthe bestjfitmodel,nativespeciesbiomass,litter%c,%n,andc:nratioallhadapositiveeffect onsoilcstocks,thoughtheywerenotstatisticallysignificant.thecandidatemodel containingnativespeciesbiomass,littermass,litter%cand%n,andc:nratiowasthebest fitmodelforpredictingsoilnstocks(table2j4;wi=0.72).inthismodel,nativespecies biomassandlittermassbothhadasignificantnegativeeffectonsoilnstocks,withlitter masshavingaslightlylargereffect.thoughnotsignificant,litter%candc:nratiohada negativeeffectonsoilnstocks,whilelitter%nhadapositiveeffectonsoilnstock.for soilquality(c:nratio),themodelthatcontainedlitter%nastheonlypredictorvariable wasthebestjfitmodel(table2j4;wi=0.76).inthebestjfitmodel,litter%nhada significantpositiveinfluenceonsoilc:nratios,meaningasthelitterncontentincreasedso didsoilc:nratios. OfthefourcandidatemodelspredictingecosystemCstock,themostparsimonious containedbothinvasivespeciesandnativespeciesbiomass(table2j5;wi=0.74).forthis model,invasivespeciesbiomasshadasignificantpositiverelationshipwithecosystemc stock(figure2j6).forecosystemnstock,thecandidatemodelcontainingonlynative speciesbiomasswasthemostapproximating(table2j5;wi=0.51),thoughthenullmodel hada AIClessthan2givingsupporttobothmodels.ForthebestJfitmodel,nativespecies biomasshadasignificantnegativerelationshipwithecosystemnstock,meaningthatas nativespeciesbiomassincreased,ecosystemnstocksdecreased,whichissimilartothe relationshipnativespeciesbiomasshadonsoilnstocks. 43

61 Soil*carbon*quality*assay Carbonmineralization(CJmin)rateswerefairlyconstantoverthedurationofthe 36Jdayincubationformosttreatmentcombinations,exceptforthePhalarissoilathigh temperature,whichdecreasedoverthefirst15daysbutthenstabilizedthroughouttheend oftheincubation(figure2j7;significantthreejwayinteraction,p=0.001;table2j6). PhalarissoilathightemperaturealsohadthegreatestCJminratesoverthedurationofthe experiment.athightemperature,typhasoilcjminratesweresignificantlylessthan Phalaris,butgreaterthanPhragmites,suggestingthatPhalarissoilwasthemostlabileand Phragmiteswasthemostrecalcitrant.CarbonmineralizationrateofPhragmitessoilathigh temperaturewasnotstatisticallydifferentfromphalarissoilatlowtemperature.thesame rankorderofsoillabilitywasfoundatlowtemperatureandhightemperature:phalaris> Typha>Phragmites(significantspeciesmaineffect,p=0.03;Table2J6).Asexpected, carbonmineralizationathightemperaturewasgreaterthanlowtemperatureamongall species(significanttemperaturemaineffect,p<0.001;table2j6). CumulativeCJminshowedapatternsimilartoCJminrates:Phalarissoilhadthe greatestcumulativecjmin,followednextbytyphasoil,andthenfinallyphragmitessoil, andthispatternwasthesameatbothtemperatures,thoughhightemperaturesledto highercumulativecjminthanlowtemperatures(figure2j8;significantmaineffectsof speciesandtemperature,p=0.03andp<0.001,respectively;table2j7).similartocjmin rates,cumulativecjminresultssuggestthatphalarissoilismorelabilethaneithertyphaor Phragmitessoil,withthelatterbeingtheleastlabile. ThereweresignificantspecieseffectsonpreJincubationsoil%C,%N,andC:Nratio (Table2J8).TyphaandPhragmitessoilhadhighestsoil%C,whilePhalarishadthelowest 44

62 (significantspecieseffect,p<0.05).soil%nfollowedasimilarpatternwithtyphaand Phragmiteshavingthegreatestsoil%NandPhalaristheleast(significantspecieseffect,p= 0.05).Althoughnotsignificant,Typhadidhaveagreateramountofsoil%Nthan Phragmites,whichisreflectedintheirdifferenceinsoilC:Nratio.SoilC:Nratiowasthe highestinphragmitessoilandlowestintyphaandphalarissoil(significantspecieseffect,p =0.01).Phalaris*arundinaceasoilC:Nratioshowedthemostvariationandwasnot statisticallydifferentfromtyphasoil. Todetermineiflitterchemistryfollowedasimilarpatternassoilchemistry,litter %C,%N,andC:Nratioswereanalyzedforspecieseffects(Table2J8).Therewasno differenceinlitter%camongspecies,butphalarishadthehighestlitter%ncomparedto TyphaandPhragmiteslitter(marginallysignificantspecieseffect,p=0.08).LitterC:Nratio followedasimilarpatternassoilc:nratio:phragmiteslitterhadthehighestlitterc:nratio andphalarishadthelowestlitterc:nratio(significantspecieseffect,p=0.03). TodeterminepossiblecontrolsoncumulativeCJmin,linearandnonlinear regressionwasusedtoverifythepredictedinfluencesoilc:nratio(quality)hason decompositionrates.aspredicted,therewasanegativerelationshipbetweencumulative CJminathigh(Figure2J9;adjustedR 2 =0.53,p<0.001)andlow(Figure2J9;adjustedR 2 = 0.40,p<0.001)temperaturesandsoilC:Nratio.SoilC:Nratiowasabetterpredictorof cumulativecjminthansoil%c(hightemperature:adjustedr 2 =0.28;lowtemperature: adjustedr 2 =0.24)or%N(hightemperature:adjustedR 2 =0.17;lowtemperature: adjustedr 2 =0.12). 45

63 Asdiscussedinthemethodssection,Q10isametricthatdescribestherateof changeinabiologicalorchemicalsystemwithanincreaseof10 C,andusingQ10allowsa comparisontobemadeoftemperatureeffectsoncjminratesduetospecies.thoughthere wasapatterntotheeffectspecieshadonq10,withtyphasoilhavingthelowestq10and PhragmitesandPhalarissoilhavingalmostequalQ10,thiswasonlymarginallysignificant (Figure2J10;F2,8=3.46,p=0.083).TheseresultssuggestthatTyphasoilismoreresistant totheeffectsoftemperaturechangethantheotherspecies soil. N*mineralization*and*nitrification*assay PotentialNmineralizationandnitrificationrateswerealmostidenticalbecausethe majorityoftheammoniummineralizedwasnitrifiedtonitrate.nitrogenmineralization ratesweregreatestinphalarissoilandtheleastintyphasoil(figure2j11;significant specieseffect,f2,5=20.93,p=0.003).nitrificationfollowedasimilarpattern,though slightlylessso(marginallysignificantspecieseffect,p=0.06).thelownmineralization andnitrificationratesofphragmitessoilisinagreementwiththecjminresultsthat suggestedphragmites*soilismorerecalcitrantthansoilcollectedfromotherinvasive speciesmonospecificstands.thoughtherewerenosignificantdifferencesinsoilc:nratios amongthethreesoilscollectedforthisincubation(p=0.46),thereweresignificant differencesamongspeciesforsoil%cand%n(significantspecieseffect,bothp<0.01; Table2J9).ThesedifferencesweremainlycausedbyPhragmitessoilhavinggreater%C and%n,thoughtyphasoildidhaveslightlygreater%cthanphalarissoil.soilc:nratio 46

64 didnothaveasignificantrelationshipwithnmineralizationrates(adjustedr 2 =0.04,p= 0.17). 47

65 Table2J2.SummaryofthebestJfitmodelforbiomassCandNstocks.Dominance referstotheproportionofthetotalbiomassfrominvasiveornativespecies.terms inboldindicatesignificantpredictors.df(den)indicatesthedenominatordegreesof freedom. Biomass*C*Stock* Term estimate tjvalue Df(Den) PJvalue InvasiveSpeciesDominance NativeSpeciesDominance Biomass*N*Stock* Term estimate tjvalue Df(Den) PJvalue Total(Biomass( <0.001 Table2J3.SummaryofthebestJfitmodelforlitterCandNstocksandlitterC:Nratios. Termsinboldindicatesignificantpredictors.Df(Den)indicatesthedenominator degreesoffreedom. Litter*C*Stock* Term estimate tjvalue Df(Den) PJvalue Biomass%N Biomass%C J2.50 J BiomassC:N Litter*N*Stock* Term estimate tjvalue Df(Den) PJvalue Biomass%N Litter*Quality*(C:N*Ratio)* Term estimate tjvalue Df(Den) PJvalue InvasiveSpeciesBiomass Biomass(%N( J15.97 J <

66 Table2J4.SummaryofthebestJfitmodelforsoilCandNstocksandsoilC:Nratios. Termsinboldindicatesignificantpredictors.Df(Den)indicatesthedenominator degreesoffreedom. Soil*C*Stock* Term estimate tjvalue Df(Den) PJvalue Invasive(Species(Biomass( NativeSpeciesBiomass Litter(Mass( J0.97 J Litter%C Litter%N LitterC:N Soil*N*Stock* Term estimate tjvalue Df(Den) PJvalue Native(Species(Biomass( J0.48 J Litter(Mass( J0.13 J Litter%C J4.37 J Litter%N LitterC:N J0.83 J Soil*Quality*(C:N*Ratio)* Term estimate tjvalue Df(Den) PJvalue Litter(N( Table2J5.SummaryofthebestJfitmodelforecosytemCandNstocks.Termsinbold indicatesignificantpredictors.df(den)indicatesthedenominatordegreesof freedom. Ecosystem*C*Stock* Term estimate tjvalue Df(Den) PJvalue Invasive(Species(Biomass( NativeSpeciesBiomass Ecosystem*N*Stock* Term estimate tjvalue Df(Den) PJvalue Native(Species(Biomass( J0.43 J

67 Table2J6.ResultsofrepeatedmeasuresANOVAfortheeffectofSpecies, TemperatureandTimeonCmineralizationthroughoutthe36dayincubation. Between*Subjects* * Source numdf dendf F PJvalue Species Temperature < Speciesx Temperature Within*Subjects* * Source numdf dendf F PJvalue Time TimexSpecies TimexTemperature TimexSpeciesx Temp ** Table2J7.SummaryofANOVAexaminingtheeffectofSpeciesand TemperatureoncumulativeCmineralization. Source df dendf F P>F Species Temperature < SxT

68 Table2J8.Soilandlitter%C,%N,andC:Nratioofthefourspeciesusedinthe organicmatterqualityincubation.samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.valuesaremeans ±SE. Litter Litter Litter Species Soil%C Soil%N SoilC:N %C %N C:N Phragmites* ±4.2 a ±0.31 a ±0.5 a ±1.5 ±0.20 a ±6.9 a Phalaris* Typha* Carex* ±3.1 b 18.2 ±2.4 a 10.5 ±3.2 b ±0.21 b 1.56 ±0.22 a 0.88 ±0.28 b ±0.8 b 11.7 ±0.3 b 12.1 ±0.6 b ± ±3.5 ±0.20 b 1.23 ±0.15 a ±3.4 b 34.3 ±6.6 c no*data* no*data* no*data* Table2J9Soil%C,%N,andC:Nratioofthefourspecies usedinthenmineralization/nitrificationincubation. Samelettersuperscriptdenotesnonsignificant differencesaccordingtotukeyposthoctests.valuesare means±se. Species Soil%C Soil%N SoilC:N Phragmites* 31.7±4.9 a 2.27±0.35 a 14.0±0.4 Phalaris* 4.3±0.8 b 0.30±0.06 b 14.7±0.7 Typha* 8.5±2.3 c 0.59±0.16 b 14.7±0.7 51

69 1.4" 1.2" Shannon&Diversity& 1" 0.8" 0.6" 0.4" 0.2" 0" 0" 0.2" 0.4" 0.6" 0.8" 1" Invasive&Species&Dominance& Figure2J1.Regressionbetweeninvasivespeciesdominance(percentbiomassof community)andshannondiversityindex(adjustedr 2 =0.75,p<0.001). 52

70 Site%NUE% 160" 140" 120" 100" 80" 60" 40" 20" 0" 0" 100" 200" 300" 400" 500" 600" 700" 800" Figure2J2.Regressionbetweeninvasivespeciesbiomass(cumulativebiomassof Phragmitesaustralis,Phalaris*arundinacea,and*Typhaspp.)andsitenitrogenuseefficiency (adjustedr 2 =0.10,p=0.08). Invasive%Species%Biomass%(g%m 52 )% 53

71 Total&Biomass&(g&m -2 )& 900" 800" 700" 600" 500" 400" 300" 200" 100" 0" 0" 100" 200" 300" 400" 500" 600" 700" 800" 900" Invasive&Species&Biomass&(g&m -2 )& Figure2J3.Regressionbetweeninvasivespeciesbiomass(cumulativebiomassof Phragmitesaustralis,Phalaris*arundinacea,and*Typhaspp.)andtotalbiomass(adjustedR 2 =0.61,p<0.001). 54

72 60" 50" Li#er&C:N&Ra,o& 40" 30" 20" 10" 0" 0.6" 0.8" 1" 1.2" 1.4" 1.6" Biomass&%&N& Figure2J4.Regressionbetweenbiomass%NandlitterC:Nratio(adjustedR 2 =0.32,p< 0.001).Biomass%NwasasignificantpredictorinthebestJfitmodelforlitterC:Nratios. 55

73 8000" 7000" Soil%C%Stock%(g%m -2 )% 6000" 5000" 4000" 3000" 2000" 1000" 0" 0" 200" 400" 600" 800" 1000" Invasive%Species%Biomass%(g%m -2 )% Figure2J5.Regressionbetweeninvasivespeciesbiomass(cumulativebiomassof Phragmitesaustralis,Phalaris*arundinacea,and*Typhaspp.)andsoilCstock(adjustedR= 0.27,p<0.001).InvasivespeciesbiomasswasasignificantpredictorinthebestJfitmodel forsoilcstock. 56

74 Ecosystem)C)Stock)(g)m /2 )) 9000" 8000" 7000" 6000" 5000" 4000" 3000" 2000" 1000" 0" 0" 100" 200" 300" 400" 500" 600" Invasive)Species)Biomass)(g)m /2 )) Figure2J6.Regressionbetweeninvasivespeciesbiomass(cumulativebiomassof Phragmitesaustralis,Phalaris*arundinaceaand*Typhaspp.)andecosystemCstock (adjustedr 2 =0.35,p<0.001).Invasivespeciesbiomasswasasignificantpredictorinthe bestjfitmodelforecosystemcstock. 57

75 C-Min Rate (g CO 2 -C kg -1 SC day -1 ) Day of Incubation Phalaris HT Phragmites HT Typha HT Phalaris LT Phragmites LT Typha LT Figure2J7.Carbonmineralizationratesoverthe36Jdaylaboratoryincubation.Repeated measuresanovashowedthattherewasasignificant3jwayinteractionbetweenspecies, temperatureandtime(f2,494=7.00,p=0.001).errorbarsrepresent1se. 58

76 120" c Total&C&Mineraliza.on&(g&CO 2 3C&kg 31 &SC)& 100" 80" 60" 40" 20" a b ae Low"Temp"(7"C)" High"Temp"(23"C)" e d 0" Typha& Phalaris& Phragmites& Species& Figure2J8.MeancumulativeCmineralizationoverthe36Jdaylaboratoryincubation.The maineffectsofspecies(f2,8=5.82,p=0.028)andtemperature(f2,47= ,p<0.001) weresignificant,butnottheirinteraction.samelettersuperscriptdenotesnonsignificant differencesaccordingtotukeyposthoctests.errorbarsrepresent1se. 59

77 250" TotalCMineraliza.on(gCO 2 3Ckg 31 SC) 200" 150" 100" 50" High"Temp"(23"C)" Low"Temp"(7"C)" 0" 10" 11" 12" 13" 14" 15" 16" 17" 18" SoilC:NRa.o Figure2J9.RegressionbetweensoilC:NratioandcumulativeCmineralizationathigh (21 C;adjustedR 2 =0.53,p<0.001)andlow(7 C;adjustedR 2 =0.40,p<0.001) temperatures. 60

78 Q 10$ 2.9$ 2.7$ 2.5$ 2.3$ 2.1$ 1.9$ 1.7$ 1.5$ Phragmites+ Phalaris+ Typha+ Species$ Figure2J10.ComparisonofmeanQ10valuesamongsoilcollectedfrommonospecific standsofphragmites*australis,phalaris*arundinacea,andtyphaspp.theeffectofspecies wasmarginallysignificant(f2,8=3.46,p=0.082).errorbarsrepresent1se. Net$N$Min$(mg$N$kg,1 $SC)$ 160" 140" 120" 100" 80" 60" 40" 20" 0" a Phragmites+ Phalaris+ Typha+ b Species$ Figure2J11.ComparisonofmeannetNmineralizationratesamongsoilcollectedfrom monospecificstandsofphragmites*australis,phalaris*arundinacea,andtyphaspp.the effectofspecieswassignificant(f2,5=22.32,p=0.003).samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se. b 61

79 Discussion ThenegativerelationshipbetweeninvasivespeciesdominanceandShannon diversityisapatternthathasbeenfoundininvestigationsatsimilarspatialscales(sakaiet al.2001;hejdaetal.2009),thoughtherelationshipisn tusuallyasstrongastheonefound inthiswetlandsurvey(figure2j1).conversely,houlahanandfindley(2004)foundlittle evidenceforinvasivespecieshavingalargereffectthannativesonplantdiversityin58 Ontarioinlandwetlands,thoughcommunitydominants(nativeorexotic)diddecrease diversity.wheninvasiveplantssuccessfullyinvadetheyusuallyoutjcompeteotherplants andeitherreducetheirpopulationand/orcausethemtogolocallyextinct(sakaietal. 2001;Allendorf2003).Thisconsequenceofinvasionusuallycausesspeciesdiversityto declineonalocalscale(thoughonlargerspatialscalesspeciesdiversitycanincrease becauseatlargerspatialscalesthosespeciesthatarethreatenedatsmallerspatialscales stillpersist).thestrongpatternseeninthisstudylikelyispartlyduetowetlandsbeing particularlysusceptibletoinvasionduetotheirhydrogeomorphicplacementonthe landscapethatresultsinhighlevelsofdisturbance,nutrientenrichment,andpropagule pressure(zedlerandkercher2004).additionally,wetlandinvasivespeciesareknownto formmonospecificstands,whichreducelocaldiversitytoanevengreaterextent. WhileIfoundsomesupportformypredictionthattherewillbeapositive correlationbetweenthedegreeofinvasionandtheoverallplantcommunitynue(figure 2J2),thispatternwasdrivenentirelybyLLP(sitedominatedbyPhragmites).Thelackofa relationshipissomewhatsurprisingbecausewetlandinvasivespeciesareknowntousually producegreateramountsofbiomassthannatives(ehrenfeld2003;liaoetal.2008)and, therefore,eitherhavehighernueorareusingalargernpoolthannatives.myresults suggestthelatterandcouldbeconnectedtothetheirabilitytorespondtolargernpools 62

80 thannatives(davisetal.2000)thataremoreadaptedtolownconditions(daehler2003), thoughnotalways(funkandvitousek2007).whiletherehavebeensimilarstudies investigatingnueofinvasivespecies(funkandvitousek2007),thisisthefirst,thatiam awareof,thathaslookedatthenueoftheentirecommunity.futurestudiesshould investigatethenpoolsusedbywetlandinvasivespeciescomparedtonativeplantsto determineifinvasivespeciesdousealargernpoolthannatives. ThemostparsimoniousmodelforbiomassCstockincludedbothinvasiveand nativespeciesdominance,thoughneitherhadasignificantrelationshipwithbiomassc stock.therelationshipbetweenbiomasscstockandinvasivespeciesdominanceis reasonablebecauseinvasivespeciesareusuallyhighbiomassproducingspecies(ehrenfeld 2003;Liaoetal.2008),sothemoredominanttheyarethemoreCshouldbein abovegroundbiomass.thepositiveinfluenceofnativespeciesdominanceisharderto explain,butcouldindicatethatspeciesidentity(invasiveornative)didn ttrulymatter. TotalbiomasswasthebestpredictorofbiomassNstocksuggestingthatregardlessof communitycomposition(nativeorinvasive),wetlandswithmorebiomassalsohadmoren storedintheabovegroundbiomass.thisisfurtherevidenceforinvasivespeciesnot havingahighernuethannativespeciesbecauseotherwisetherewouldlikelynotbea relationshipbetweentotalbiomassandbiomassnstocksasinvasivespeciesconstitutethe majorityofthebiomassatmostofthesesites. ThebestJfitmodelsforlitterCandNstockscontainedtissuechemistrypredictors withbiomass%nandc:nratioshavingapositiveeffectandbiomass%canegativeeffect. Theseindividualvariableswerenotsignificant,however,andforlitterNstocktherewas notastatisticalsignificancebetweenthebestjfitmodelandthenullmodel,sowhiletissue 63

81 chemistrytraitslikelydoinfluencelittercandnstocks,inthisdatasetitishardtohave confidenceintheirimportance.themostparsimoniousmodelforlitterc:nratiohadboth nativespeciesandbiomass%naspredictorvariables,thoughonlybiomass%nwas significant.asmentionedintheresultssection,thenegativerelationshipfoundbetween litterc:nratioandbiomass%n(asbiomass%nincreases,litterc:nratiodecreases) showsthelinkbetweenlivingbiomassnutrientconcentrationsandthelitterquality;the livingbiomassncontentinfluencedthelitterbyincreasingthequality(loweringthec:n ratios)asncontentincreased.thelinkbetweenlivingtissuechemistryandlitterqualityis alogicalrelationshipbuthasnotbeenshownbeforeatthecommunitylevelasinthis study,thoughithasbeeninferred(wardleetal.2004).thelackofinvasivespecies influenceonlittercandnstocksandqualityrefutedpredictions2.2and3.1,andshowed that,asawhole,invasivespeciesdon tdifferfromnativesintheirabilitytoalterlitter stocksandquality.thisconclusionissupportedbyherrjturoffandzedler(2005)that foundthatphalarisinvasiondidnotalterawetland sabilitytoretainn.itshouldbestated, though,thatthelittercollectedinthewetlandsurveywaslitterthathadaccumulatedon thesoilsurfaceovermultiplegrowingseasonsandthereforemightnotbeanindicatorof freshlitterquality. ThoughthefullmodelwasthebestJfitmodelforsoilCstocks,onlyinvasivespecies biomassandlittermassweresignificant.thepositiveinfluenceinvasivespecieshadon soilcstockssupportshypothesis3thatasthedominanceofinvasivespeciesincreasesso willtheorganicmatterstorageofthewetlandstheyinvade(figure2j5).thisrelationship wasalsoseeninametajanalysisbyliaoetal.(2008)thatfoundinvasivespeciesincreased rootcstockby5%andshootcstockby133%.additionally,heetal.(2011)foundthat 64

82 PhalarishadagreaterseasonalCgaincomparedtothenativespeciesCarex*stricta.The negativeinfluenceoflittermassseemscounterintuitiveasmorelittermassshouldmean moreorganicmatterbeingincorporatedintothesoil,but,asmentionedabove,thelitter collectedinthewetlandsurveywaslitterthathadaccumulatedonthesoilsurfaceover multiplegrowingseasons.theaccumulationofthelittermaybeduetotherecalcitranceof thelitter,i.e.,lowerqualitylitterresisteddecompositionandthuswasnotaddedtothesoil Cstocks.ThenegativerelationshipfoundbetweenlittermassandsoilNstocksfollowsthe samelogicusedforitssamerelationshipfoundwithsoilcstocks.asforthenegative relationshipbetweennativespeciesbiomassandsoilandecosystemnstocks,thiscouldbe causedbynativespecieshavinglowerdetritalnconcentrationsorcouldbeafunctionof nativespeciesproducinglessbiomassthaninvasives.therefore,wetlandsthataremore dominatedbynativesproducelessbiomass,andsincebiomassnstockswasafunctionof totalbiomassinthisstudy,thosewetlandsmighthavelessorganicninputs(ehrenfeld 2003). Thepositiverelationshipbetweenlitter%NandsoilC:Nratiosseems counterintuitiveiflitternwasdirectlyincorporatedintosoilomasinmelilloetal.(1989) becauseonewouldexpectsoilc:nratiotodecreaseaslitterwithhigherncontentwas incorporatedintothesoil.similartotheeffectsoflittermassonsoilcandnstocks,this relationshipcouldbecausedbythelittercollectedinthisstudyhavingaccumulatedover multipleyears,soitispossiblethathavinghigherlitter%nmightbeindicativeofnbeing lockedupinlitterandnotbeingincorporatedintothesoilornimmobilizationinthelitter (Melilloetal.1989). 65

83 ForecosystemCstocks,invasivespecieshadapositiveinfluenceontheCstorage withinthewetlandssurveyedinthisstudy(figure2j6).thisisinsupportofhypothesis3 andsuggeststhatinvasiveplantspeciesplayanimportantroleintheecosystem functioningoftemperatewetlands.duetothenatureofthissurveystudy,theexact mechanismsbywhichinvasivespecieswereaffectingwetlandcstorageisunknown,but thereisevidencefromthecontrollingfactorsoftheothercandnstocksinthisstudythat planttraitssuchasbiomassnconcentrationandlitterqualitycouldbeimportant.since therewasn taneffectofinvasivespeciesonlittercandnstocksorquality,invasive speciesmaybeinfluencingsoilandecosystemcstocksbygreaterbelowgroundbiomass productionthannatives(liaoetal.2008).manystudieshavefoundthatphragmites,* Phalaris,andTyphaspp.producemorebelowgroundbiomass(andoverallbiomass)than natives(greenandgalatowitsch2001and2002;vymazalandkropfelova2005). Understandinghowwetlandsfunctionchangesfollowinginvasionsiscriticalifweareto properlymanagethesenearlyubiquitousinvasions,andifthereisapositiveaspectto invasion,suchasincreasecstorage,thenthisneedstobeconsideredwhendetermining managementforinvasivewetlandspecies.moredetailedresearchisneededtodetermine thedegreeandmechanismofthisapparentrelationship. Whilethecumulativeeffectofinvasivewetlandplantspecies(Phragmites,Phalaris, andtypha)wereshowninthisstudy,theirdifferencesinkeyplanttraits,suchaslitter quality,isimportanttoelucidateasthesespecieslikelyhaveuniqueindividualeffectsonc andncycling(eviner2004).theresultsofthecarbonqualityincubationclearlyshowed thattherearedifferencesincmineralizationratesfromsoilcollectedwithinmonospecific standsofeachofthesespecies(figure2j8),whichisinsupportofhypothesis4.soil 66

84 collectedunderpopulationsofphalarishadthegreatestcmineralizationrates,followedby TyphaandthenPhragmites.ThissuggeststhattheOMinPhalarissoilwasthemostlabile ofthethreespeciesandthislabilitycanbeconnectedtophalarishavingthehighestquality soilandlitter,whilephragmiteshadthelowestqualitysoilandlitter.thedifferenceamong theseinvasivespeciesinlitterqualitycouldalsoexplainwhytherewasnotaclear relationshipbetweeninvasivespeciesbiomassandlitterqualityinthewetlandsurvey. Theimportanceofsoilqualityondecompositionwasfurtherillustratedbythestrong relationshipbetweensoilc:nratioandtotalcmineralization,whichwasstrongerathigh temperaturesthanatlowtemperatures.therelationshipbetweenomquality(c:nratios) andcmineralizationhasbeenshowninotherstudies(melilloetal.1982;tayloretal. 1989;XuandHirata2005;Partonetal.2007),andfurthersupportstherolesoilqualityon decomposition.thedifferencebetweentemperaturesislikelycausedbygreatermicrobial activityathighertemperaturesthatprobablyenhancesthecontrollingeffectofthequality oftheorganicmatter. ThoughthedifferenceamongspeciesintheQ10responsewasonlymarginally significantlydifferent(figure2j10),becausetyphasoilhadthelowestq10value(2.13) andthuswasthemostresistanttotheeffectsoftemperaturechange,typhamonospecific standsmaybelessalteredbyawarmingclimate,thoughthedifferenceamongspecieswas minimal.therangeofq10valuesamongstudiesspecies(2.13to2.47)fellwithintherange of1.6to4.8foundforwetlandsoils(nieveenetal.1998;bubieretal.2003;lafleuretal. 2005)andtheQ10forPhragmites,2.47,wasveryclosetowhatZhouetal.(2009)found (2.38)forsoilcollectedwithinmonospecificstandsofPhragmitesinNortheastChina.In 67

85 comparisontootherecosystems,therangeifoundinthestudyspecieswassimilartowhat Bekkuetal.(2003)foundfortemperate(2.9),tropic(2.1)andarctic(3.4)soils,though arcticsoilswereabout1q10greaterthanphragmitesmonospecificstands. PhalarissoilhadthehighestNmineralizationandnitrificationrates,which correspondedwithphalarissoilhavingthehighestcmineralizationrates(figure2j11). ThisshowedthatPhalarissoilwasmoreactiveintheselaboratoryincubationscompared totyphaandphragmites,givingfurthersupporttohypothesis4.nmineralizationrates werenotcorrelatedwithsoilc:nratioand,additionally,soil%cand%ndidnotmatch thosefoundforthecqualityincubationfortworeasons:(1)soilusedinthecquality incubationwascollectedfroma5cmdepthandsoilusedinthenmineralization incubationwascollectedfroma10cmdepthand(2)adifferentmonospecificstandof PhragmiteswasusedinplaceofNLCLPthathadmuchgreatersoil%C.Specifically,usinga deepersoilcorecouldhaveincorporatedmoremineralmaterialandthusdecreasesoil%c and%nasseenincomparingthesoilfromthetwoincubations(tables2j8and2j10). Similartotheseresults,Bridghametal.(1998)foundthatNmineralizationvariedgreatly acrossanombrotrophicjminerotrophicgradientinnorthernminnesotaandthatthe dominantwetlandcommunityhadstrongdirectandindirecteffects. TheCandNmineralizationratesdifferencesamongspeciesappeartobea consequenceof oratleastcorrelatedwith differencesinplanttraits,suchaslitter quality.thoughitwasusefultolookatthecumulativeeffectsoftheseinvasivespecies,itis justasimportanttobeawareoftheirspeciesjspecificdifferencestobetterunderstand theirindividualeffects.speciesdifferencesareknowntoinfluencemanyaspectsof ecosystemfunctioning(evinerandchapin2003;wardleetal.2004)andthesedifferences 68

86 canbeespeciallyimportantwhendeterminingtheeffectsofspecies,likeinvasivespecies, thatcandominatelargespatialareas,likewetlands,thatare hotspots forbiogeochemical cycling. 69

87 Chapter(3( Effects(of(Aboveground(Biomass(and(Litter(on(Biogeochemical(Cycling(in(Phragmites) australis(stands( Brief(Rationale( TheresultsfromChapter2showedthatinvasivespecieshaveaneffectonCandN stocksandorganicmatterquality,andthattheseeffectslikelydifferamongthethree invasivespeciesstudied(phragmites*australis,phalaris*arundinacea,andtypha*spp.). WhileonlytwositesweredominatedbyP.*australis*(hereafterPhragmites)inthewetland survey,thosesiteshadthemostbiomassandsoilorganicmatterofallsitessurveyed. Additionally,speciesJspecificinvestigationintosoilandlitterqualityshowedthatsoil beneathmonospecificstandsofphragmiteshadhighsoilc:nratios(lowquality)and decomposedmoreslowlycomparedtothosedominatedbyp.*arundinaceaandtyphaspp.. Itisthereforecriticaltoinvestigate,inmoredetail,themechanismsbywhichPhragmites altersthewetlandsitinvadesduetoitslargeandexpandingdistributionintheunited States.* Phragmitesisacosmopolitanwetlandspeciesfoundonallcontinentsexcept Antarctica(CronkandFennessy2001).InsomeareasofEurope,Phragmitesisindecline andwetlandrestorationandmanagementhavefocusedonincreasingitspresenceand spread.innorthamerica,phragmiteswasonlyaminorcomponentofwetlandvegetation forthousandsofyears,butisnowoneofthemostaggressivewetlandinvadersinthe UnitedStates(Chambersetal.1999).Thespreadoftheaggressivegenotypeisattributed tomultipleeuropeanintroductionsalongthenorthernatlanticcoastinthe19 th century (Plutetal.2011).Thoughtheexactoriginoftheinvasivegenotypeisnotknown,recent evidencesuggeststheunitedkingdomasthemostlikelysource(plutetal.2011).this 70

88 genotypeissalttolerantandcanmaintainhorizontalclonalgrowth(upto4.5metersper year)allowingittoestablishandspreadincoastalwetlandsdisplacingnativeplants,such asspartinaspp.onceestablishedontheeastcoast,theeuropeangenotypesquicklyspread andarenowfoundinall48conterminousstates(chambersetal.1999).thenative genotypeismuchlessaggressivethantheexotic,whichisnowoutcompetingnative Phragmites,aswellasmostotherwetlandplantsinsiteswhereitbecomesestablished (Plutetal.2011). Itscapacityforhorizontalgrowthandsalttolerancemakesroadsideditchesin northernclimates,whereroaddeicingsaltsareused,idealenvironmentsforinvasionand spread.phragmitescangrowtoheightsof4j5metersallowingittooutcompetemost wetlandplantsforlight.additionally,thestandingdeadstemsofphragmitesusuallyresist decompositionandpersistinwetlandsforyears(graneli1990;schieferstein1997; Gessner2001).Thelargeamountoflitterproducedeveryyearshadesthesoilsurface furtherrestrictingcompetitors accesstolight.inadditiontotheeffectsphragmitescan havetothenativeplantcommunity(andothertrophiclevels),itcanalsoimpactnutrient cycling.ottoetal.(1999)showedthatinorganicnavailabilitywashigherinphragmites standscomparedtolythrum*salicariaandtypha*angustifoliastands,whilefindlayetal. (2002)founddetritalNstandingstocksweregreaterinpopulationsofPhragmitesversus T.*angustifolia.ThepresenceofPhragmitesusuallyleadstoorganicmatterbuildup,which canchangenotonlythecstorageofthewetland,butthehydrologyaswell(ableetal. 2003).WhiletheabovestudieshavebeenabletoshoweffectsofPhragmitesinvasionon biogeochemicalcycling,fewstudieshavetriedtoelucidatethemechanismsofchange.it hasbeenshownthatradialoxygenloss(rol),thelossofoxygenthroughtherooting 71

89 systemofemergentwetlandplants,isimportantforthehealthandsurvivalofphragmites* (ArmstrongandArmstrong2001;Colmer2003;Soukupetal.2007),*anditispossiblethat thisoxygenreleaseintherootingzonecouldhaveimpactsonbiogeochemicalcyclingby creatingoxidizingconditionsinanotherwiseanaerobicenvironment. ItisimportanttounderstandthemechanismsbywhichPhragmitesaltersthebiotic andabioticenvironmentbecausethenwemaybeabletopredicttheconsequencesof Phragmitesinvasionandpossiblyinvasionsbyotherspecieswithsimilartraits,aswellas tobettermanagetheirimpact.forexample,ifitisfoundthatthelitterofphragmites significantlyreduceslightlevelsatthesoilsurface,thenthepracticeofkillingstandswith glyphosateandthenleavingthelitterstandingmightnotbeadvantageousbecauseofthe negativeeffectslowlightlevelscouldhaveonnativerecruitment.onewaytodetermine thesemechanismsistomanipulateboththelitterandbiomassinafieldexperimentand thenmonitorboththeabioticenvironmentandcandncyclingwithinmanipulatedplots. Objectives,(Hypotheses,(and(Predictions( Objective:TodeterminethemechanismsbywhichPhragmitesinfluencesecosystem functioninthefield.phragmitesinvasionislikelytocausechangestothesoil microenvironment(e.g.,temperature,redoxpotential,etc)duetothehighproductionof biomass,withramificationsforsoilmicrobialactivityandbiogeochemicalprocesses,such asnandccycling,butalsoplantavailablecationsandanions.suchchangesareimportant tounderstandthefullimpactofphragmitesinvasion,aswellasattemptederadication. ( Hypothesis:Phragmitesexertsbothdirectandindirectinfluencesonbiogeochemistry; 72

90 directeffectsincludeplantnutrientuptakeintolivebiomassandindirecteffectsinclude changesinthesoilmicroenvironmentandinommatterinputqualityandquantity.asa result,ipredictthefollowing: RemovalofPhragmiteslitterwill(increaselightlevelstothesoilsurface,whichwill resultinincreaseddiurnalmaximumsoiltemperature,thoughlivingbiomass shouldstillshadesoil.increasedtemperaturewillenhancein*situnmineralization anddecompositionratescomparedtoreferenceplots.cessationoflitterinputsalso willdecreaseomqualityofthesoilasthelabileompoolismineralizedandnot replenishedtothesamedegreeasinthereferenceplots,thougheffectsonom qualitylikelywouldtakemorethanafewyearstobecomedetectable. Removaloflivingbiomass(willincreaselightlevelstothesoilsurface,whichwill resultinincreaseddiurnalmaximumsoiltemperature,thoughthelitterlayershould stillprovidepartialshadingofthesoil.increasedtemperatureshouldenhancein* situnmineralizationanddecompositionratescomparedtoreferenceplots. ReducedNandotherplantnutrientuptakebyvegetationshouldincreasetheirsoil poreconcentration.additionally,thesedimentanoxiczoneshouldincreaseduetoa reductioninradialoxygenlossfromrootingsystem. Becausethetotalremovaltreatmentwasinitiatedin2010,asoilorganicmatter effectwouldprobablytakeyearstobecomedetectable.thistreatmentwasmainly establishedtodeterminelightlevelsandtemperatureintheabsenceofbothlitter andvegetation.thetotalremovalofboththelivingbiomassandlitterofphragmites shouldresultinthegreatestincreaseinlightlevelstothesoilsurface,whichwill 73

91 resultinincreaseddiurnalmaximumsoiltemperature.thisincreasedtemperature shouldenhancein*situnmineralizationanddecompositionratescomparedtoall othertreatments,butthegreatestdifferenceshouldbewhencomparedtoreference plots. Methods( Site*description*and*experimental*treatment*design* Iconductedafieldexperimentthatmanipulatedabovegroundbiomassandlitter levelsinthreetemperatewetlands.theexperimentwasdesignedtoquantifythedirect andindirecteffectsofphragmites*onthesoilmicroenvironmentandbiogeochemical cycling.threesiteswereselectedin2008thatweremonospecificstandsofphragmites*of similarsize(seebelow);twositeswerelocatedwithinlakelansingparkincentrallower Michigan(Figure3J1;42 o N85 o W);athirdsitewaslocatedwithinawetland environmentsurroundingglasbylakeinsouthwesternmichigan(figure3j2;42 o N 85 o W). LakeLansingParkisembeddedinamosaicoflakes,woodlots,andresidentialareas. Thetotalareaoftheparkis166hectaresandconsistsmainlyofdeciduousforest, coniferousforest,andalargeinterconnectedwetlandcomplexofapproximately80 hectares.theparkhasbeenextensivelyinvadedbyavarietyofinvasiveplantspecies, includingphragmites,*p.*arundinacea,andtypha glauca.thewetlandcomplexcontainsa mosaicofmonospecificstandsofthesethreespecies,thoughsomeareasaremixturesof thesealongwithsomenativespecies.someofthemoreconspicuousnativespeciesinclude Carexspp.,Juncusspp.,Sambucusspp.,Leersia*oryzoides,Eutrochium*maculatum,*Impatiens* spp.,andasclepias*incarnata.bothllpsitesconsistedofpurestandsofphragmitesofa 74

92 totalarealessthan1hectare.llp1waslocatedwithinaninletofthemajorwetland complexthatdominatesthepark,whilellp2wasseparatedfromthemajorwetland complexbyareasofhigherelevationandagravelroad.duetothisspatialseparationand differenthydrology(seeresults)thesetwositeswereconsideredindependent. Subsequenttothecompletionofthisresearch,beginningin2011,theLLPsiteswere subjectedtocontrolmeasuresintendedtoeradicatephragmitesfromwithinthepark. TheexperimentalwetlandsiteadjacenttoGlasbyLake(referredtohereafteras Glasby)wassimilarinsizetoLLP1andLLP2withotherinvasivespeciessuchasP.* arundinaceaandt. glaucasurroundingthephragmitesstand,comparabletothellp sites.theregionaroundglasbylakeliesonaglaciallandscapeandhasabundantwetland cover(~10%)withlowlevelsofresidentialdevelopmentinalandscapedominatedby forests,rowjcropagriculturalfields,andabandonedfields.glasbylakeitselfis approximately10hectaresofopenwaterwithmoreextensivewetlandssurroundingthe lake.theamountsofliveanddeadphragmitesbiomass,aswellassoilandwater characteristics,atthesethreesitesarecomparedintable3j1.thedatafortable3j1were collectedoverthegrowingseasonsof2008j2010andthemethodologyusedtocollectthe fielddatacanbefoundinappendixb. Toseparatetheeffectsoflivingvegetationversuslitteronthesoilmicroenvironment andbiogeochemicalcycling,experimentalmanipulationoflitterandabovegroundliving biomass(agb)wasinitiatedinthesummerof2008.ateachofthethreesitesdescribed above,icreatedten2x2m(4m 2 )plotsrandomlydistributedthroughoutthesite,and assignedeachplottoeitherareference,anagbremoval,alitterremoval,oratotal removaltreatment(n=3foralltreatmentsexceptn=1fortotalremovaltreatment).i 75

93 markedthecornerofeachwithpvcthatstood1mfromthesoilsurfaceforthreecorners oftheplotand3mforthefourthcorner.thesetenplotswererandomlyestablished withineachsiteandtheneachplotwasrandomlyassignedatreatment.vegetationwas clearedaroundeachplot(0.5m)toestablishabufferzoneandnoexperimentalsamples (exceptforagb)werecollectedwithin20cmfromtheouteredgeoftheplottoreduce edgeeffects.theheightofthesestandsexceeded3mandthusthebufferzonehadlittle effectonlightpenetrationtothegroundsurface.referenceandbiomassremovalplots wereestablishedatthebeginningofthegrowingseasonin2008,litterremovalplotsatthe beginningofgrowingseasonin2009,andtotalremovalplotsatthebeginningofthe growingseasonin2010. ForAGBremovaltreatmentplots,allindividualplantswerecutatthesoilsurfaceand removedfromtheplot(standingandfallenlitterremained).forlitterremovaltreatment plots,allstandingandfallenlitterwascollectedbyhandandremovedfromtheplot(agb remained).forthetotalremovalplots,allagbandlitter(standingandfallenlitter)was removedbyhand.totalremovalplotswereestablishedtodeterminelightlevelsand temperatureintheabsenceofbothlitterandvegetation.litterandagbwerenotaltered inthereferenceplots.manipulationsweremaintainedeverythreeweeksduringthe growingseason(maytooctober)byremovinganyvegetationregrowthfromtheagb removalplotsandanynewlyfallenlitterinthelitterremovalplots.inthefallof2009,all ofthesenescedagbinthelitterremovalplotswascutatthesoilsurfaceandmovedtothe AGBremovalplotstopreventanylitterdepositioninlitterremovalplots,aswellasto ensuretheagbremovalplotscontinuedtoreceivelitterinputs.monitoringofthe referenceandmanipulationplotsstartedingrowingseasonof2008(may)andcontinued 76

94 throughthegrowingseasonof2009andendedpastthegrowingseasonof2010 November).WhilerootdecaymayhaveoccurredintheAGBremovalplots,because regrowthfromrhizomespersistedthroughoutthegrowingseason,itisunlikelythat substantialrootdecompositionoccurred.regardless,rootsandrhizomeswereremoved fromsoilcorescollectedforassaysthatmightbeinfluencedbyrootdecay,e.g.,forthein* situnmineralizationassay. Abiotic*and*biotic*measurements Tomonitorwatertablelevels,Solinstpressuretransducerswereinstalledateachsite alongwithsolinstbarometricpressureloggerstocorrectforatmosphericpressure. Pressuretransducersweresuspendedwithina~1.5JmlongPVCpipewithholesdrilled throughthesidestoallowwatertoenterthepipe.pvcpipeswheresurroundedwitha smallmeshsizematerialtokeepsoilanddebrisfromentering.pressuretransducers withinthepvcstructurewereinstalledinarandomlyselectedplot1mbelowthe soil/sedimentsurface.pressuretransducerswereinstalledinearlysummerof2008,2009, and2010andremovedinlateoctobereachyeartoavoidwinterdamageandtodownload data.watertablemeasurementsin2008weretakenonlyatllp1andglasby.manual waterlevelmeasurementswerealsotakenateachploteverythirdweekofthegrowing season.allplotsexperiencedrelativelysimilarhydrologicconditionswithinasite, thereforeitispossibletocomparesitehydrologicconditionsbasedonpressuretransducer measurementsatasinglepoint. Todeterminetreatmenteffectsonsoilcharacteristics,soilsampleswerecollectedat eachplotattheendofthegrowingseasonandanalyzedforbulkdensity,%moisture,and 77

95 %CandNtodetermineCandNstorage.Surfacesoilwassampledtoa10cmdepthusinga soilcorer (246cm 3 )andsamplesweretransportedtothelaboniceandkeptat4 Cuntil processed(~3days).forprocessing,soilsweresieved(4mm),subjsampledforbulk densityandgravimetricwatercontent(gwc)determination,andthendriedtoaconstant massat80 C.Driedsoilswerethengroundandhomogenizedusingamortalandpestle andrunonanelementalcombustionsystem(costechecs4010,valencia,ca)for%cand %Nanalysis.Sampleswereruninduplicatewithatropineusedasastandardevery10 samples.forthesoilsamplescollectedin2010,the10cmsoilcoresweresplitintotwo depths,0j5cmand5j10cm,andanalyzedseparately,includingfornh4 + +NO3 J concentration(seenmineralizationandnitrificationmethodsbelow)todetermine possibledeptheffects. Surfacewatersamplesweretakenonamonthlybasisduringthe2009and2010 growingseasonsasbaselinedatatocompareamongsitesandtodeterminetreatment effectsonwaterchemistry(table3j1).thesethreesitesvariedseasonallyandamong yearsinthepresenceanddepthofwaterabovethesoilsurface.watersampleswere collectedwhenstandingwaterwasgreaterthan5cmusinga250mlpolyethylenebottle submergedbelowthewatersurface.sampleswereanalyzedforsolublereactive phosphorus(srp),ammonium,totalalkalinity,dissolvedorganiccarbon(doc),andother majorcationsandanions(no3 J,Cl J,Na +,Mg 2+,Ca 2+,K + ).Dissolvedoxygen,specific conductivity(spc),watertemperature,ph,andoxidationjreductionpotential(orp)were monitoredusinganysi556multijprobesystem. AfterallexperimentalmanipulationswereestablishedatthethreePhragmitessites, 78

96 HOBOloggingthermistorswereinstalled(4verticalpositions:ambient[60cmabovesoil surface],litterlayer,andat2jand10jcmsoildepths)atonerandomplotpertreatmentper sitetodetermineiftheexperimentaltreatmentsaffectedlitterandsoiltemperatures. From8Julyto29October2010soiltemperaturesatsixdepths(soilsurface,2,10,20,30, 40cm)weremanuallymeasuredwithaMultiloggerThermometer(OMEGAEngineering, Inc.)ateachtreatmentplotateachsite.Manualtemperaturemeasurementsweremadeto checktheaccuracyofhobotemperatureprobemeasurements,aswellasforanalysisof depthprofiles.insummer2010,lightlevels(photosyntheticallyactiveradiation)atthe groundlevelwithineachplotwereestimatedmonthlyusinganaccuparlpj80 Ceptometer(ICTInternational). * Litter*bag*decomposition*assay* Toquantifyin*situdecompositionratesalitterbagassaywasperformedusingboth PhragmitesstemtissueandWhatmancellulosefiltersasastandardsubstrate.Litterbags (10cmx10cm)werecreatedusingNylonmesh(meshsize=0.25mm)andthread. Approximately1gofairJdriedPhragmitesstemlitterwasplacedinthelitterbag,along withoneairjdriedwhatmancellulosefilterpaper(90mmdiameter,~1.12g).samplesof theairjdriedstemlitterandfilterpaperweredriedtoaconstantmassat80 Cand weighed,andthepercentdifferencewasusedtocorrecttheairjdriedweights.thelitter bagswerethensealedusingaheatedhandimpulsesealerwithplasticasthesealant.litter bagswereconnectedwithbraidednylonfishinglinetoamarkerflagandtheneither placedonthesoilsurfaceor10cmbelowthesoilsurface.fivelitterbagswereplacedin eachplot,threeonthesoilsurfaceandtwoat10cmbelowthesoilsurface(total=150 79

97 litterbags:90atsoilsurface,60at10cmsoildepth).litterbagswereinstalledineachplot on29july(glasby)and30july(llp1andllp2)in2010.after18daysinthefield,one randomlyselectedsoilsurfacelitterbagwasremovedfromeachplot,returnedtothelab, andkeptat4 Cuntilprocessed.Afteratotalof42and90daysinthefield,onesurfaceand oneburiedlitterbagwereremoved(randomlyselected),returnedtothelab,andkeptat 4 Cuntilprocessed.Duringthetimethelitterbagswereinthefield,waterlevelswere~ 19cmabovethesoilsurfaceatGlasby,55cmbelowthesoilsurfaceatLLP1andfellfrom5 cmabovethesoilsurfacetobelowthesoilsurfaceatllp2.forprocessing,litterbagswere gentlywashedwithdistilledwatertoremovethemajorityofthesoilparticles.the cellulosefilterwasseparatedfromthestemlitter,placedinaluminumfoil,driedtoa constantmassat80 Candweighed. Porewater*equilibrators Toinvestigatepossibletreatmenteffectsonthechemistryofwaterintherootzone, porewaterequilibratorswereinstalledateachsiteforapproximately20days,from11 August(Glasby),12August(LLP2),and16August(LLP1)2011to31August,1September, and2september2011,respectively.atglasbyandllp2,aporewaterequilibratorwas installedatonerandomlyselectedreference,agbremoval,andlitterremovaltreatment plot.atllp1,duetolowwatertablelevels,porewaterequilibratorswereonlyinstalledat areferenceandagbremovalplot.theporewaterequilibratorswereconstructedoutof clearacrylicplasticwithatotallengthof60cmandwidthof10cm.fourteenpairedwells ranfromtoptobottomoftheporewaterequilibrator(3.5cmdistancebetweenwellpairs) witheachwellholding12mlofwater.beforeinstallation,eachporewaterequilibratorwas 80

98 submergedinfilteredwater(pallsupor450membrane)andonebiotrans TM nylon membrane(0.2µmporesize)filtermembranesheetwaslaidontopoftheporewater equilibrator,coveringthewells.thefaceplatewasthensecurelyfastenedtosealthe membraneoverthewellopenings.eachporewaterequilibratorwasthenplacedina verticalacrylictankfilledwithfilteredwateranddeoxygenatedovernightbypumpingn2 gasthroughabubblerintothebottomofthetankforapproximately12hours.tanks containingtheporewaterequilibratorswerethentransportedindeoxygenatedwaterto eachsite.forinstallation,porewaterequilibratorsweredrivenintothesoiluntilonlythe toptwowellpairswereabovethesoilsurfaceinthesurfacewater(llp2andglasby).due tolowwatertablelevels,installationatllp1includeddiggingapilotholetodeterminethe locationofthewatertableandtheninstallingtheporewaterequilibratortothatdepth. Afterapproximately20daysinthefield,porewaterequilibratorswereremovedand analyzedfortotaldissolvedp,no3 J,Cl J,Na +,Mg 2+,Ca 2+,K + andsilicate. N*mineralization*and*nitrification*assays Inthesummerof2010,in*situnetNmineralizationandnitrificationrateswere assayedineachplotusingtheburiedpolyethylenebagtechnique(eno1960;binkleyand Hart1989).ConductingtheNtransformationassayinthefieldisusefulbecausepossible treatmenteffects,suchastemperaturedifferences,canbeincludedintheincubation. Threepairsofsoilcores(10cmdepth,246cm 3 )wereremovedfromeachplot(6coresx 10treatmentplotsx3sites=180cores).Soilcorepairsweretakenfromarandom locationwithineachplot,withadistanceof5cmbetweenpairedsoilcores.onecorefrom 81

99 eachpairwasplacedinapolyethylenebagandburiedatthesamedepthitwastaken,while theothersoilcorewastransportedonicetothelaboratoryforinitialnpoolsize determination.soilcoreswereincubatedinthefieldfrom15julyto15august(30days), afterwhichtheyweretransportedtothelabforfinalnpoolsizedetermination.fromthe timeofinitialin*situ*setuptotheendoftheincubation,waterlevelswereabovethesoil surfaceatglasbyandllp2,whileatllp1thewatertablewas~20cmbelowthesoil.for processing,soilsweresieved(4mm),subjsampledfordeterminationofbulkdensity, gravimetricwatercontent(gwc)andconcentrationsofnh4 + andno3 J,andthendriedtoa constantmassat80 C.Driedsoilsweregroundusingamortalandpestleandanalyzedon anelementalcombustionsystem(costechecs4010,valencia,ca)for%cand%n. ConcentrationsofinorganicNforbothinitialandfinalsoilcoresweredeterminedon subsamplesofallsoilsviaextractionwith2mkclandanalyzedbythemicroplatemethod fornitrateandammoniumusingprotocolsdevelopedbydr.davidrothstein(dept.of Forestry,MSU).NetratesofNmineralizationandnitrificationwerecalculatedfromthe changesininorganicn(nh4 + +NO3 J )orno3 J JN,respectively,duringtheincubationperiod (initial finalpoolsizes). Denitrification*assay Alaboratorydenitrificationassaywasperformedtodeterminetreatmenteffectson denitrificationpotential.on5november2011,a10cmsoilcore(246cm 3 )wascollected fromeachtreatmentplotateachsite,transportedtothelabonice,andkeptat4 Cuntil processed.atthetimeofsoilharvest,waterlevelswereabovethesoilsurface(~30cm)at 82

100 Glasby,atthesoilsurfaceatLLP2,andbelowthesoilsurfaceatLLP1.On6November 2011,soilcoresweresieved(4mm)andthentwosubsamples(25ml)werekeptoniceand transportedtodr.jennifertank slabattheuniversityofnotredamewheretheassaywas performed(10treatmentplotsx3sitesx2replicatesubsamples=60assaysamples).on7 November2011,denitrificationratesweredeterminedusingthechloramphenicolJ amendedacetylene(c2h2)inhibitiontechnique(groffmanetal.2006)modifiedbythe TankLab.Briefly,each25mlsubsamplewasaddedtoa125mlmediabottleand50ml unfilteredwaterfromtheglasbysitewasaddedandmixedwiththesoiltomakeaslurry. ThemediabottlewassealedwithannJbutylrubberseptuminthelidtoallowgassamples tobecollectedwitha5mlsyringe.chloramphenicolwasaddedtotheslurrytoinhibitde* novoenzymeproduction.beforegassamplesweretaken,theheadspaceofthemediajars waspurgedwithheliumfor10minutesandmechanicallyagitatedtoachieveanoxic conditionsthroughouttheslurry.acetylenegas(15ml)wasthenaddedtothemedia bottletopreventtheconversionofn2oton2,allowingtheconcentrationofn2otobeused fordenitrificationratedetermination.five5mlgassampleswerecollectedstartingattime 0andthenhourlyfor4hours(totalof5samplesperreplicate).Sampleswereinjectedinto a3mlscintillationjarandthenanalyzedforn2oonagaschromatographwithanelectron capturedetector.denitrificationrateswerecalculatedforeachreplicatefromthelinear increaseinn2oconcentrationoverthecourseofthe4jhourincubation.concentrations werecorrectedfordilutionbytheadditionofn2aftereachsamplewascollectedandrates wereexpressedonavolumetricandgravimetricbasis. 83

101 Statistical*analyses Sitedifferencesinkeysoilcharacteristicswereanalyzedbygenerallinearmodels (GLM)tohelpexplainthepatterninvariationamongsitesfortheecosystemprocessdata collectedinthisstudy.fourseparatemultivariateanalysisofvariance(manova)tests wereperformedfortwosetsofresponsevariables:1)litterbagdecompositionrate, denitrificationrate,netnmineralizationrate,andnitrificationrate(hereafterrate responsevariables),and2)soilcharacteristicscollectedin2010.foreachsetofresponse variablestheeffectsoftreatmentandsiteweretestedindividuallyforatotaloffour MANOVAtests.ThemultivariateanalysiswasusedtoprotectfollowJupANOVAanalysis frominflatedalpha,whichcanhappenwhenmultipleanovatestsareperformed (Scheiner2001).ThePillaiJBartletttrace(hereafterPillai)wasusedastheteststatisticfor eachmanova.separateglms(anovas)werethenruntoassesswhichfactors significantlyinfluencedindividualresponsevariables. Fortheanalysisoflightlevels,soiltemperature,soilCandNstorage,soilNH4 + and NO3 J concentrations,in*situnetnmineralization/nitrificationrates,potential denitrificationrates,andlitterbagdecompositionrates,glmswereusedtodetermine treatmenteffects.fortheseanalyses, site wasconsideredarandomfactorand plot was nestedwithin site.porewaterequilibratordatawereanalyzeddifferentlybecausethere wasnoreplicationatthetreatmentplotlevel,insteadtherewasonlyoneequilibratorper treatmentpersite,andthereforeplotwasnotnestedwithinsite.additionally,depthwas includedasafixedfactorforthoseanalysesthatincludedit.tukey shsdmultiple comparisontestswereperformedtodeterminesignificantdifferencesamongfactorlevels. 84

102 Forthebiogeochemicalrateassays(Nmineralization,nitrification,denitrification, anddecomposition),bothsimplelinearregressionandmultipleregressionanalyseswere performedtodeterminesignificantcontrollingsoilfactorsonrates.manyofthe measurementsandassaysdescribedabovewereadditionallyanalyzedwith site asafixed effect(without treatment asafixedeffect)becauseofthestrongsiteeffectsthatwere present,whichcanbelinkedtodifferencesinhydrology.modeldiagnosticswereassessed foreachanalysistodetermineiftheresidualswerenormallydistributedanddisplayed constanterrorvariances.logtransformationswereusedtocorrectforany heteroscedasticity.allvariancesarepresentedasstandarderrors.allstatisticaltestswere performedinr2.13.2(rdevelopmentcoreteam2011). ( ( ( ( ( ( ( ( 85

103 Table3(1.Variationamongsitesinplantcharacteristics,soilcharacteristics,andwaterchemistry.Varianceexpressed asstandarderror.agb=abovegroundbiomass,do=dissolvedoxygen,spc=specificconductivity,orp=oxidation reductionpotential,om=organicmatter.*indicatesdatacollectedin2010. PlantCharacteristics(2009) Site PlantHeight (cm) AGB (g) AGBpertiller (g) Standinglitter (gm (2 ) GroundLitter (gm (2 ) TotalLitter (gm (2 ) Rhizome (gm (2 ) LLP1 361± ± ± ± ± ± ±186 LLP2 383± ± ± ± ± ± ±596 Glasby 391± ± ± ± ± ± ±576 SoilCharacteristics(2009) Site OMDepth (cm) Bulkdensity (gcm (3 ) Ammonium* (mgnkg (1 ) Nitrate* (mgnkg (1 ) Soil%C Soil%N SoilC:N LLP1 66.7± ± ± ± ± ± ±0.48 LLP2 55.2± ± ± ± ± ± ±0.68 Glasby 53.9± ± ± ± ± ± ±0.34 WaterChemistry(2010) SpC DO Salinity ORP Site (µscm (1 ) (mgl (1 ) %DO ph (ppt) (mv) LLP ± ± ± ± ±0.04 (179±56 LLP ± ± ± ± ±0.06 (5±11 Glasby 0.442± ± ± ± ±0.04 (18.2±14 MajorIons(ppm;2009and2010) Site Cl ( (ppm) NO3 ( (ppm) SO4 2( (ppm) Ca 2+ (ppm) Mg 2+ (ppm) Na + (ppm) K + (ppm) LLP ± ± ± ± ± ± ±0.64 LLP ± ± ± ± ± ± ±0.77 Glasby 56.88± ± ± ± ± ± ±

104 Table3(1(continued) Roots TotalBGB (gm (2 ) (gm (2 ) 149± ± ± ± ± ±812 SoilCStock SoilNStock (gm (2 ) (gm (2 ) 6368± ± ± ± ± ±74 87

105 km ± LLP Site 2 [ [ LLP Site 1 Lake Lansing Figure3)1.MapshowingthelocationofthetwomonospecificstandsofPhragmites+ australisatlakelansingpark(llp1andllp2),haslett,mi. 88

106 Village of Delton Upper Crooked Lake Glasby Lake Site [ ± km Figure3)2.MapshowingthelocationofthemonospecificstandofPhragmites+australisin thewetlandareasurroundingglasbylake(glasby),delton,mi. 89

107 Results Site+Characteristics Forsoilcharacteristics,multivariateanalysisshowedsignificanteffectsofsiteand depth(pillai=1.51,approx.f16,48=16.06,p<0.001,pillai=0.57,approx.f8,41=6.84,p< 0.001,respectively).Therewasalsoasignificantsitexdepthinteraction(Pillai=0.51, approx.f16,84=1.80,p=0.045).protectedunivariateanalysisshowedtherewere significantsiteeffectsfornitrate,ammonium,andsoilc:nratio(table3)2).llp1soilhad greaternitrateavailabilityandlowersoilmoistureandammoniumavailabilitythaneither LLP2orGlasby,whileGlasbyhadahighersoilC:NratiothanLLP1andLLP2.SoilCandN stocksandsoil%candnwerealsosignificantlydifferentamongsites(table3)2).there wasasignificantsitexdepthinteractionforbothsoil%c(p=0.040)and%n(p=0.085): LLP1andGlasbyhadgreatersoil%CandNat0)5cmdepthcomparedtoat5)10cmdepth, buttherewerenodifferencesbetweendepthsatllp2.soilcandnstocksfolloweda similarpatternofhigherstocksat5)10cmdepthcomparedtoat0)5cmdepth(significant deptheffect;p<0.001forbothsoilcandnstock),alongwithllp1havinggreaterstocks thanllp2andglasby(significantsiteeffect;table3)2). Watertablepositionmeasuredin2008)2010(Figures3)3to3)5)bypressure transducersinstalledateachsiteareinformativebecausetheyhelptoexplainthevariation amongsitesformanyofthevariablesdiscussedabove.thereareanumberofpointstobe madeaboutthewatertablepositiondata: 90

108 (1)Glasbyhadahigherwatertablepositionthroughoutallrecordedtimeperiods comparedtollp1,whilellp2hadthehighestwatertablepositionthroughout 2009andthesecondhighestpositionin2010; (2)Wetandcoolspringandsummerconditionsin2009leadtohigherthanaverage waterlevelsacrosscentralmichigan,leadingtohighwatertablepositionat LLP1andLLP2; (3)InSeptemberof2008and2010,therewasadramaticincreaseinwatertable positionformostsitesfollowingheavyrainfall; (4)In2010,whenmostofthedataanalyzedabovewerecollected,theGlasbywater levelwasalwaysatleast10cmabovethesoilsurface,whilellp1 swaterlevel wasalwaysbelowthesoilsurface.llp2 swaterlevelwasclosertothesoil surfaceandshiftedfromabovetobelowthesoilsurfacemultipletimesover therecordedperiodin2010. AsummaryoftheaveragewatertablepositioncanbefoundinFigure3)6.Thesesite differencesinhydrologylikelyexplainthevariationinsoilmoisturedifferencesamong sites:llp2hadthegreatestsoilmoisture,followedbyglasby,andthenllp1(significant siteeffect;p<0.001). Whiletherewaslittledifferenceintotalabovegroundbiomassproductionandplant heightamongsites,therewasasignificantsiteeffectonrhizome,root,andtotal belowgroundbiomass(bgb)(totalbgb:f2,12=8.35,p=0.005).glasby,themost consistentlysaturatedsite,hadthehighestbgb,whilellp2andllp1,whichhadeither fluctuatingwaterlevelsorwaterlevelsconsistentlybelowthesoilsurface,hadsignificantly lowerbgb. 91

109 Litter+and+AGB+effects+on+soil+and+porewater+chemistry,+light+levels,+and+temperature+ Forsoilcharacteristics,resultsfromtheMANOVAindicatedthatwhenanalyzedfor theeffectsoftreatmentanddepth,treatmentwasnotsignificant(pillai=0.23,approx. F16,84=0.69,p=0.798)butdepthwas(Pillai=0.51,approx.F8,41=5.41,p<0.001). ProtectedANOVAsindicatedbulkdensity,stocksofsoilCandN,andsoilC:Nratiowereall significantlygreaterat5)10cmdepthcomparedtoat0)5cmdepth(table3)3). Conversely,ammonium,nitrate,andsoil%CandNwereallsignificantlygreaterat0)5 depthcomparedtoat5)10cmdepth(table3)3). Photosyntheticallyactiveradiation(PAR)belowthecanopyvariedacross treatmentswiththehighestvaluesrecordedinthetotalremovalplots(781±191µmolm )2 sec )1 ),nearly18foldgreaterthaninthereferenceplots(44±15µmolm )2 sec )1 )(Figure3) 7;significanttreatmenteffect,p<0.001).LevelsofPARinthebiomassremovalandlitter removalplotswereintermediate,anddidnotstatisticallydifferfromoneanother. Averagedacrosssites,soiltemperaturemeasurementsmadeduringmiddayvisits rangedfrom17.1±0.54 o Catadepthof40cmforthereferencetreatmentto24.77±2.67 o Catthesoilsurfaceforthetotalremovaltreatment(Figure3)8).Inalltreatmentsbesides totalremoval,therewasagradualdecreaseintemperaturefromambientto40cmsoil depth(significantdeptheffect;table3)4).forthebiomassremovaltreatment,therewasa significantdecreaseintemperaturefromambientairtothesoilsurfacefollowedbya decreasefromasoildepthof2cmto40cmsimilartoothertreatments(significant treatmentxdepthinteraction;table3)4).thetotalremovaltreatmentshowedanincrease 92

110 intemperaturefromambienttosoilsurface,thoughtheywerenotsignificantlydifferent. Referenceplotshadthelowestrecordedsoiltemperatureforeachsoildepth,aswellas ambienttemperature(significanttreatmenteffect;table3)4). ForHOBOdataloggertemperaturemeasurementsrecordedin2010,whichincluded allfourtreatmentplots,therewasaninteractionbetweendepthanddate:temperature variationamongdayswasgreaterforambientairreadingscomparedtosoilreadings (Figures3)9to3)12;significantdepthxdateinteraction;Table3)5).From12Julytothe beginningofseptember,totalremovalplotshadthehighesttemperaturesfollowedby litterremovalplots,biomassremovalplots,andreferenceplots.startingatthebeginningof Septemberandlastinguntiltheendoftherecordingperiod(28October),therankorderof decreasingtemperaturechangedtoreference,biomassremoval,totalremoval,andfinally litterremoval(significanttreatmentxdateinteraction;table3)5).thesignificant treatmenteffect(p=0.003)wascausedbytotalremovalplotshavinghighertemperatures comparedtheothertreatmentlevels,fromthestartoftherecordingperiodto approximatelythebeginningofseptember. Analysisofporewaterequilibratorwellsafterfieldincubationrevealeddistinct changesinmajorsolutechemistrywithdepthbelowthewatertable.therewasa significanttreatmenteffectonna + andcl ) concentrations,asthebiomassremoval treatmentplotshadlowerconcentrationsoftheserelativelyconservativeionscomparedto thereferenceandlitterremovalplots(figures3)13and3)14;significanttreatmenteffect; Table3)6).ConcentrationsofMg 2+ werehighestinthelitterremovalplotscomparedto referenceandbiomassremovalplots(figure3)15;significanttreatmenteffect;table3)6) 93

111 andthispatternwasstrongeratgreaterdepth,thoughtheinteractionwasnotsignificant. ConcentrationsofCa 2+ werehighestinreferenceplotscomparedtobiomassandlitter removalplots(figure3)16;significanttreatmenteffect;table3)6).acrosstreatments, Mg 2+ andca 2+ concentrationsincreasedwithdepth(significantdeptheffect;table3)6). Sulfateandnitratedecreasedwithwelldepth(Figure3)17and3)18;significantdepth effect;p<0.001),andthoughtherewerenosignificanteffectsoftreatmentforsulfate, nitratewassignificantlylowerinreferenceplotsthanlitterremovalplots(significant treatmenteffect;p=0.049,table3)6).totaldissolvedphosphate(tdp)andpotassiumdid notvarywithdepthoramongtreatments. Carbon+and+nitrogen+cycling Forthecarbonandnitrogencyclingrateresponsevariables(litterbag decompositionrate,denitrificationrate,netnmineralizationrate,andnitrificationrate), therewerenosignificanteffectsoflitterand/orbiomassremovaltreatment(manova; Pillai=0.30,approx.F15,72=0.52,p=0.919),butthatthereweresignificantsiteeffects (Pillai=1.29,approx.F10,48=8.74,p<0.001). Forunivariateanalysis,therewerenosignificanttreatmenteffectsonin+situN mineralizationornitrificationrates,thoughtherewerestrongsiteeffects.bothglasbyand LLP2hadpositiveNmineralizationrates(3.99and4.96mgNkg )1 soil,respectively)while negativenmineralization(i.e.,netimmobilizationand/ordenitrificationofdissolved inorganicn)occurredatllp1()0.88mgnkg )1 soil)(figure3)19;significantsiteeffect, 94

112 F2,87=65.57;p<0.001).NetnitrificationrateswerenegativeforLLP1andLLP2()0.39 and)0.15mgnkgsoil )1,respectively)andzeroforGlasby(Figure3)20;significantsite effect,f2,87=1.29;p<0.001).becausellp1andllp2hadpositivesoilnitrate concentrationsatthebeginningoftheincubation,thelownetnitrificationrateswerelikely causedbydenitrification(nitrateloss)occurringthroughoutthe30)dayincubation.soil moistureandsoil%nwerepositivelyrelatedtonetnmineralization(figure3)21and3) 22;adjustedR 2 =0.297,p<0.001,adjustedR 2 =0.406,p<0.001,respectively). Ammoniumwaspositivelyrelatedtosoilmoisture(Figure3)23;adjustedR 2 =0.125,p< 0.001),whilenitratewasnegativelyrelatedtosoilmoisture(adjustedR 2 =0.045,p< 0.025),thoughtherelationshipwasweak. Therewerenotreatmenteffectsonlitterbagdecompositionrates,thoughthere weresignificantdeptheffects.trendsindecompositionweresimilarforbothphragmites stemsandfilterpaper:filterpaper(figure3)24;p<0.001;table8)andstem(figure3)25; p=0.015;table3)7)materialincubatedwithinsoilhadalowerdecompositionrate comparedtowhenincubatedonthesoilsurface,thoughtherewerenodifferenceswithin totalremovalplots.whenlitterbagassaydatawereanalyzedtodeterminesitexdepth effects,theirinteractionwasfoundtobesignificant.forstemdecomposition,ratesatboth depthsatllp1andglasbywerenotdifferentfromoneanother,butatllp2stemtissue decomposedfasteronthesoilsurfaceandslowerinsoilcomparedtollp1andglasby (Figure3)26;significantsitexdepthinteraction;Table3)7).Forfilterpaper decomposition,therewasnostatisticaldifferenceamongsitesforfilterpaperincubatedin 95

113 soil,whilefilterpaperincubatedonthesoilsurfacedecomposedfaster.thisfaster decompositiononthesoilsurfacewasnotobservedatllp1(figure3)26;significantsitex depthinteraction;table3)7).overall,filterpaper(kconstant=0.0114d )1 )decomposedat afasterratethanphragmitesstemtissue(kconstant=0.0022d )1 )(p<0.001). Similartothein+situNmineralization/nitrificationincubationandlitterbagassay, nosignificanttreatmenteffectswerefoundforpotentialdenitrificationrates.therewere strongsiteeffects,andexpressingdenitrificationratesonavolumetric(cm )3 )or gravimetric(g )1 soilandg )1 soilc)basisyieldedsimilarresults:bothllp1andllp2had significantlygreatern2oproductionratesthanglasby(figure3)28;p<0.001forallcases; forcm )3 F2,27=11.41),whichhadalmostnodetectableamountofN2Oproduction. Becausemodeofexpressiondidnotaffectstatisticalconclusions,onlydenitrificationrates expressedonavolumetricbasis(cm )3 )willbediscussedfurther.thebestfitmultiple regressionmodel(basedonaicvaluesandoverallmodelsignificance)showed denitrificationrateswerepositivelyrelatedtosoilnitrate(figure3)29;p<0.001)and negativelyrelatedtosoilc:nratio(figure3)30;p<0.001),withtheoverallmodel explaining41%ofthevariationindenitrificationrates. 96

114 Table3(2.MixedmodelF(valuesfortheeffectofSiteandDepthonBulkDensity,Ammonium,Nitrate,Soil%C,Soil%N, SoilC:Nratio,andSoilCandNStock.dfindicatesdegreesoffreedom.Significanceisdenotedwithasterisk(s). Source df BulkDensity Ammonium Nitrate Soil%C Soil%N SoilC:N SoilCStock SoilNStock Site ** 23.10** 18.44** 53.50** 65.52** 23.25** 4.76* 7.88** Depth ** 8.21* 6.07* 7.12* 16.80** 17.11** 33.80** 19.79** TxD * * 2.58* 3.72* *p<0.05 **p<0.001 Table3(3.MixedmodelF(valuesfortheeffectofTreatmentandDepthonBulkDensity,Ammonium,Nitrate,Soil%C, Soil%N,SoilC:Nratio,andSoilCandNStock.dfindicatesdegreesoffreedom.Significanceisdenotedwithasterisk(s). Source df BulkDensity Ammonium Nitrate Soil%C Soil%N SoilC:N SoilCStock SoilNStock Treatment Depth ** 8.09* 6.15* 6.34* 15.16** 14.57** 33.08** 19.46** TxD *p<0.05 **p<

115 Table3(4.Summaryoftwo(factorANOVAfortheeffectofTreatment anddepthonsoiltemperature.dendfindicatesthedenominator degreesoffreedomandnumdfindicatesnumeratordegreesof freedom. Source numdf dendf F P(value Treatment < Depth < TxD Table3(5.SummaryofRepeatedMeasuresANOVAfortheeffectofTreatment, Depth,andTimeonsoiltemperatureduringthe2010growingseason.dendf indicatesdenominatordegreesoffreedomandnumdfindicatesnumerator degreesoffreedom. Between&Subjects& & Source numdf dendf F P(value Treatment Depth TreatmentxDepth Within&Subjects& & Source numdf dendf F P(value Time < TimexTreatment < TimexDepth < TimexTreat.xDepth && 98

116 Table3(6.MixedmodelF(valuesfortheeffectofTreatmentandDepthonTDP(totaldissolved phosphate),mg 2+,Ca 2+,Na +,K +,SO4 2(,Cl (,andno3 ( concentrationsfromporewater equilibrators.significanceisdenotedwithasterisk(s).dfindicatesdegreesoffreedom. Source df TDP Mg 2+ Ca 2+ Na + K + SO4 2( Cl ( NO3 ( Treatment * 7.54* 4.93* ** 3.16* Depth ** 5.44** ** * TreatmentxDepth *p<0.05 **p<

117 Table3(7.Summaryoftwo(factorANOVAsfortheeffectofTreatment anddepthonstemandfilterdecompositionandsiteanddepthon stemandfilterdecomposition(expressedasfirst(orderrateconstants, k).dendfindicatesthedenominatordegreesoffreedomandnumdf indicatesnumeratordegreesoffreedom. Source numdf dendf F P(value Stem%k%constant% % Treatment Depth TxD Filter%k%constant% % Treatment Depth < TxD Stem%k%constant% % Site Depth SxD Filter%k%constant% % Site < Depth < SxD

118 50$ 40$ Glasby$ LLP1$ Water&Level&(cm)& 30$ 20$ 10$ 0$ 10$ 20$ 30$ 40$ 50$ 7/18/08$ 8/2/08$ 8/17/08$ 9/1/08$ 9/16/08$ 10/1/08$ Date& Figure3(3.WatertablepositionatGlasbyandLLP1fromJulytoOctoberof2008.Zero waterlevelrepresentsthesoilsurfacewithpositivewaterlevelsindicatingflooding (standingwater)andnegativevaluesindicatingawatertablebelowthesoilsurface. 101

119 Water&Level&(cm)& 50$ 40$ 30$ 20$ 10$ 0$ 10$ 20$ 30$ 40$ Glasby$ LLP2$ LLP1$ 50$ 8/7/09$ 8/22/09$ 9/6/09$ 9/21/09$ 10/6/09$ 10/21/09$ 11/5/09$ Date& Figure3(4.WatertablepositionatGlasby,LLP1,andLLP2fromAugusttoNovemberof 2009.Zerowaterlevelrepresentsthesoilsurfacewithpositivewaterlevelsindicating flooding(standingwater)andnegativevaluesindicatingawatertablebelowthesoil surface. 102

120 Water&Level&(cm)& 50$ 40$ 30$ 20$ 10$ 0$ 10$ 20$ 30$ 40$ 50$ 60$ 70$ 80$ Glasby$ LLP1$ LLP2$ 7/3/10$ 7/23/10$ 8/12/10$ 9/1/10$ 9/21/10$ 10/11/10$ 10/31/10$ Date& Figure3(5.WatertablepositionatGlasby,LLP1,andLLP2fromJulytoOctoberof2010. Zerowaterlevelrepresentsthesoilsurfacewithpositivewaterlevelsindicatingflooding (standingwater)andnegativevaluesindicatingawatertablebelowthesoilsurface. 103

121 40$ Water&Level&(cm)& 20$ 0$ 20$ 40$ 60$ Glasby$ LLP1$ LLP2$ 2008$ 2009$ 2010$ Site& Figure3(6.WatertablepositionatGlasby,LLP1,andLLP2for2008to2010(seemethods forexacttimeperiods).zerowaterlevelrepresentsthesoilsurfacewithpositivewater levelsindicatingflooding(standingwater)andnegativevaluesindicatingawatertable belowthesoilsurface.errorbarsrepresent1standarddeviation. 104

122 PAR$(umol$m *2 $s *1 )$ 1000" 900" 800" 700" 600" 500" 400" 300" 200" 100" 0" a b C" BR" LR" TR" Treatment$ Figure3(7.Meanlightlevels(PAR)measureddirectlyabovethesoilsurfacewithincontrol (C),biomassremoval(BR),litterremoval(LR),andtotalremoval(TR)treatmentplots averagedacrosssites.therewasasignificanttreatmenteffect(f3,81=109.95,p<0.001). SamelettersuperscriptdenotesnonsignificantdifferencesaccordingtoTukeyposthoc tests.errorbarsrepresent1se. b c 105

123 30" 25" Temperature)(C)) 20" 15" 10" Ambient" Soil"Surface" 2cm" 10cm" 20cm" 30cm" 40cm" 5" 0" C" BR" LR" TR" Treatment) Figure3)8.Meanmanualtemperaturemeasurementstakenat6soildepths(andambient)withincontrol(C), biomassremoval(br),litterremoval(lr),andtotalremoval(tr)treatmentplotsaveragedacrosssites.there wasasignificantinteractionbetweentreatmentanddepth(f18,174=2.07,p<0.009).errorbarsrepresent1 SE. 106

124 30" 25" BR" C" LR" TR" Temperature)(C)) 20" 15" 10" 5" 0" 7/3/10" 7/23/10" 8/12/10" 9/1/10" 9/21/10" 10/11/10" 10/31/10" Date) Figure3)9.DailyambientmeantemperaturefromJulytoOctober2010withincontrol(C),biomassremoval(BR),litter removal(lr),andtotalremoval(tr)treatmentplots. 107

125 30" 25" BR" C" LR" TR" Temperature)(C)) 20" 15" 10" 5" 0" 7/3/10" 7/23/10" 8/12/10" 9/1/10" 9/21/10" 10/11/10" 10/31/10" Date) Figure3)10.DailysoilsurfacemeantemperaturefromJulytoOctober2010withincontrol(C),biomassremoval(BR), litterremoval(lr),andtotalremoval(tr)treatmentplots. 108

126 30" 25" BR" C" LR" TR" Temperature)(C)) 20" 15" 10" 5" 0" 7/3/10" 7/23/10" 8/12/10" 9/1/10" 9/21/10" 10/11/10" 10/31/10" Date) Figure3)11.Dailymeantemperatureat2cmsoildepthfromJulytoOctober2010withincontrol(C),biomassremoval (BR),litterremoval(LR),andtotalremoval(TR)treatmentplots. 109

127 30" 25" BR" C" LR" TR" 20" Temperature)(C)) 15" 10" 5" 0" 7/3/10" 7/23/10" 8/12/10" 9/1/10" 9/21/10" 10/11/10" 10/31/10" Date) Figure3)12Dailymeantemperatureat10cmsoildepthfromJulytoOctober2010withincontrol(C),biomassremoval (BR),litterremoval(LR),andtotalremoval(TR)treatmentplots. 110

128 Well$Depth$(cm)$ 0" 5" 10" 15" 20" 25" 30" Cl$(ppm)$ 0" 20" 40" 60" 80" 100" 120" 140" 160" 35" C" 40" BR" 45" LR" 50" Figure3)13.MeanCl ) concentrationsfromporewaterequilibratorswithincontrol(c), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectoftreatment(F2,63=17.34,p<0.001)onCl ) concentrations, butnotdepthortheirinteraction.errorbarsrepresent1se. 111

129 Well$Depth$(cm)$ 0" 5" 10" 15" 20" 25" 30" Na$(ppm)$ 0" 10" 20" 30" 40" 50" 60" 70" 80" 35" C" 40" BR" 45" LR" 50" Figure3)14.MeanNa + concentrationsfromporewaterequilibratorswithincontrol(c), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectoftreatment(F2,63=4.93,p=0.01)onNa + concentrations, butnotdepthortheirinteraction.errorbarsrepresent1se. 112

130 Well$Depth$(cm)$ 0" 5" 10" 15" 20" 25" 30" 35" 40" 45" Mg$(ppm)$ 0" 10" 20" 30" 40" 50" 60" 50" Figure3)15.MeanMg 2+ concentrationsfromporewaterequilibratorswithincontrol(c), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectoftreatment(F2,63=3.29,p=0.043)anddepth(F13,63= 9.20,p<0.001)onMg 2+ concentrations,butnottheirinteraction.errorbarsrepresent1 SE. C" BR" LR" 113

131 Well$Depth$(cm)$ 0" 5" 10" 15" 20" 25" 30" 35" 40" 45" Ca$(ppm)$ 0" 50" 100" 150" 200" 250" C" BR" LR" 50" Figure3)16.MeanCa 2+ concentrationsfromporewaterequilibratorswithincontrol(c), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectoftreatment(F2,63=7.54,p=0.001)anddepth(F13,63= 5.44,p<0.001)onCa 2+ concentrations,butnottheirinteraction.errorbarsrepresent1 SE. 114

132 Well$Depth$(cm)$ 0" 5" 10" 15" 20" 25" 30" 35" 40" 45" Sulfate$(ppm)$ 0" 5" 10" 15" 20" 25" 30" 35" 40" 50" Figure3)17.MeanSO4 2) concentrationsfromporewaterequilibratorswithincontrol(c), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectofdepth(F13,63=4.48,p<0.001)onSO4 2) concentrations, butnottreatmentortheirinteraction.errorbarsrepresent1se. C" BR" LR" 115

133 Well$Depth$(cm)$ 0" 5" 10" 15" 20" 25" 30" 35" 40" 45" Nitrate$(ppm)$ 0" 0.2" 0.4" 0.6" 0.8" 1" 1.2" 1.4" 50" Figure3)18.MeanNO3 ) )Nconcentrationsfromporewaterequilibratorswithincontrol(C), biomassremoval(br),andlitterremoval(lr)treatmentplotsaveragedacrosssites. Therewasasignificanteffectofdepth(F13,63=3.16,p=0.049)andtreatmentonNO3 ) (F13,63=2.91,p=0.002)concentrations,butnottheirinteraction.Errorbarsrepresent1 SE. C" BR" LR" 116

134 N"Mineraliza+on"(mg"N"kg 11 "soil)" 7# 6# 5# 4# 3# 2# 1# 0# 1# 2# Glasby# LLP1# LLP2# Site" Figure3)19.MeannetNmineralizationratesamongsoilcollectedwithinmonospecific standsofphragmites+australisatglasby,llp1,andllp2.theeffectofsitewassignificant (F2,87=65.57;p<0.001).Samelettersuperscriptdenotesnonsignificantdifferences accordingtotukeyposthoctests.errorbarsrepresent1se. Nitrifica(on+(mg+N+kg 01 +soil)+ 0.2# 0# 0.2# 0.4# 0.6# 0.8# 1# a b Glasby# LLP1# LLP2# Site+ Figure3)20.Meannetnitrificationratesamongsoilcollectedwithinmonospecificstands ofphragmites+australisatglasby,llp1,andllp2.theeffectofsitewassignificant(f2,87= 1.29;p<0.001).Errorbarsrepresent1SE. a 117

135 N$Mineraliza9on$(mg$N$kg <1 $soil)$ 14" 12" 10" 8" 6" 4" 2" 0" 02" 04" 06" 0.6" 0.65" 0.7" 0.75" 0.8" 0.85" 0.9" 0.95" Soil$%$Moisture$ Figure3)21.Regressionbetweensoil%moistureandnetNmineralizationrates(adjusted R 2 =0.297,p<0.001). N$Mineraliza9on$(mg$N$kg <1 $soil)$ 14" 12" 10" 8" 6" 4" 2" 0" 02" 04" 06" 1" 1.5" 2" 2.5" 3" 3.5" Soil$%$N$ Figure3)22.Regressionbetweensoil%moistureandnetNmineralizationrates(adjusted R 2 =0.406,p<0.001). 118

136 140" Ammonium$(mg$kg <1 )$ 120" 100" 80" 60" 40" 20" 0" 0.6" 0.65" 0.7" 0.75" 0.8" 0.85" 0.9" 0.95" Soil$%$Moisture$ Figure3)23.Regressionbetweensoil%moistureandnetNmineralizationrates(adjusted R 2 =0.125,p<0.001). Stem%Decomposi,on%Rate%(d 21 )% # # # # # # # # a ab a b BR# C# LR# TR# a li/er# Treatment% Figure3)24.Meanfirstorderrateconstants(k;day )1 )forstemsincubatedwithincontrol (C),biomassremoval(BR),litterremoval(LR),andtotalremoval(TR)treatmentplotsover a90daytimeperiodaveragedacrosssites.therewasasignificanteffectofdepth(f1,44= 6.43;p=0.014),butnottreatmentortheirinteraction.Samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se. b ab a soil# 119

137 FilterDecomposi.onRate(d 41 ) 0.025# 0.020# 0.015# 0.010# 0.005# 0.000# BR# C# LR# TR# Treatment Figure3)25.Meanfirstorderrateconstants(k;day )1 )forfiltersincubatedwithincontrol (C),biomassremoval(BR),litterremoval(LR),andtotalremoval(TR)treatmentplotsover a90daytimeperiodaveragedacrosssites.therewasasignificanteffectofdepth(f1,44= 6.43;p<0.001),butnottreatmentortheirinteraction.Samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se. Stem%Decomposi,on%Rate%(d 21 )% # # # # # # # # a a b ab a b b a li.er# Site% Figure3)26.Meanfirstorderrateconstants(k;day )1 )forstemsincubatedatglasby(gl), LLP1,andLLP2sitesovera90daytimeperiod.Therewasasignificantinteraction betweensiteanddepth(f2,54=5.12;p=0.009).samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se. b ab GL# LLP1# LLP2# b c e ab soil# li-er# soil# 120

138 FilterDecomposi.onRate(d 41 ) 0.025# 0.020# 0.015# 0.010# 0.005# 0.000# GL# LLP1# LLP2# Site Figure3)27.Meanfirstorderrateconstants(k;day )1 )forfiltersincubatedatglasby(gl), LLP1,andLLP2sitesovera90daytimeperiod.Therewasasignificantinteraction betweensiteanddepth(f2,54=10.33;p<0.001).samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se. N 2 O$(µmol$cm +3 $day +1 )$$ 0.07% 0.06% 0.05% 0.04% 0.03% 0.02% 0.01% 0% 0.01% a a b c a Glasby% LLP1% LLP2% c li,er# Site$ Figure3)28.Meandenitrificationrates(N2Oproduction)amongsoilcollectedwithin monospecificstandsofphragmites+australisatglasby,llp1,andllp2.theeffectofsite wassignificant(f2,27=11.41;p<0.001).samelettersuperscriptdenotesnonsignificant differencesaccordingtotukeyposthoctests.errorbarsrepresent1se. a a c soil# 121

139 N 2 O$(µmol$cm <3 $day <1 )$$ 0.16" 0.14" 0.12" 0.1" 0.08" 0.06" 0.04" 0.02" 0" 0" 200" 400" 600" 800" 1000" 1200" Figure3)29.Regressionbetweennitrateanddenitrificationrates(N2O production)(adjustedr 2 =0.310,p<0.001). Nitrate$(mg$kg <1 )$ 0.2" N 2 O$(µmol$cm <3 $day <1 )$$ 0.15" 0.1" 0.05" 0" 00.05" 12" 12.5" 13" 13.5" 14" 14.5" 15" 15.5" Figure3)30.RegressionbetweensoilC:Nratioanddenitrificationrates(N2Oproduction) (adjustedr 2 =0.252,p<0.001). Soil$C:N$Ra9o$ 122

140 Discussion( Watertablepositionvariedamongstudysitesseasonallyandamongyears,and whenabovethesoilsurface,thedepthofstandingwatervariedaswell.thesehydrologic differencescreatedagradientinwatertablepositionamongsites,especiallyin2010,that likelyinfluencedseveraloftheresultsdiscussedabove.themorepronouncedgradientin 2010isnotablebecausethatwastheyearmostoftheinvestigationsoccurred,includingall oftheprocessrateassays.throughoutthestudyperiodin2010,thewatertablewasabove thesoilsurface(standingwater)atglasby,fluctuatedaboveandbelowthesoilsurfaceat LLP2,andwasbelowthesoilsurfaceatLLP1(Figure3)5).Differencesinwatertable positionlikelyinfluencedsitesoilmoisture,availabilityofnutrientsduetochangesin redoxpotentialcausedbydryingandrewetting,and,ifthedifferencesinhydrology occurredonalongenoughtimescale,siteorganicmatterbuildup.datasupportthese predictions;llp1(lowestwatertable)hadthelowestsoil%moisture,thelowest ammoniumconcentrations,thehighestnitrateconcentrations,andthelowestsoil%c(an estimateoforganicmatter)(table3)1).juetal.(2006)modeledhydrologiceffectsonc cyclinginforestsandwetlandsincanadaandfoundthatdrainageclassgreatlyinfluenceda wetlandsabilitytoaccumulatec,withpoorlydrainedwetlandsaccumulatingthemostand well)drainedwetlandsaccumulatingtheleast.thissupportsmyfindingsthatllp1(well) drained)hadthelowestsoil%candglasby(poolydrained)thehighest.theremainderof thissectionwillfocusontreatmentandsiteeffectsontheecosystemparametersmeasured inthisstudy,withhydrologyasthemainmechanismforvariationamongsites. Thetreatmenteffectsonbothlightlevelsandtemperaturesduringthegrowing seasonfollowedmypredictions:controlplotshadthelowestlightlevelsandthelowest 123

141 temperatures(formanualmeasurements),totalremovalplotshadthehighestlightlevels andtemperatures,andbothbiomassremovalandlitterremovalplotshadintermediate levels.thesedatasuggestanumberofeffectsofbiomassandlitterremoval.first,light levelsweredramaticallyreduced(18folddifference)inphragmitesstandscomparedto whenphragmiteswasabsent(figure3)7).second,litterandbiomassremovalboth increasedlightlevelstothesamedegree,whichwassignificantlylessofanincrease comparedtowhenitwascompletelyremoved.thisalsosupportsmypredictionsthatboth litterandbiomassremovaltreatmentswouldincreaselightlevels,buttheremaininglitter (biomassremoval)orbiomass(litterremoval)wouldreducelightlevelscomparedtowhen completelyremoved(totalremoval).similarly,farrerandgoldberg(2009)found,ina littertransplantexperiment,thattypha glaucalittersignificantlyreducessoilsurface lightlevels,but,interestingly,livet. glaucadidnotgreatlyaffectlightlevels.one explanationforthisdifferencebetweentheeffectsoflivebiomassofphragmitesandt. glaucaonlightlevelsisthatphragmitesstemshaveabranchingstructuretothem,whilet. glaucahasamuchmorelinearstructure.third,eventhoughthereweredifferencesin lightlevelsandtemperaturesamongtreatmentplots,thedifferencesinlightlevelamong plotswereofamuchgreatermagnitudethandifferencesintemperature.onepossible reasonforthismagnitudediscrepancyisthatlightleveldeterminationrequiresthe ceptometerusertorecordlightlevelsaroundnoononacloudlesssky.theseconditions producethemostextremedifferenceinlightlevelsamongtreatmentsbutarelikelynotto bethemostcommoncircumstanceeachsiteexperienced.conversely,whilemanual temperaturemeasurementsweretakenwithinasimilartimerangeaslightlevels(11:00 amto3:00pm)onrainlessdays,cloudlessskieswerenotrequisiteoftemperaturedata 124

142 collection.thesedifferenceslikelymeanthatmanualtemperaturemeasurementslikely wereclosertoactualsoilconditions.anotherpossibilityisthelowtemperatureofthe surroundingphragmitesstandsreducedthetemperaturewithinthe2x2mplots. ThetallstatureandabilityoflivingbiomassandlitterofPhragmites+toshadethe soilsurfacelikelyfacilitatesitsinvasionintonativecommunitiesbycreatinglight limitationbelowitscanopy.becausephragmitesisaclonalspecies,and,therefore,new rametscanreceiveresourcesfromparentplants,itsownsuccesswillnotbegreatly affectedbythelowlightconditions.oneconsequenceforwetlandrestorationofthe significanttreatmenteffectsonlightlevelsandtemperatureisitiscommonpracticeto managemonospecificstandsofphragmitesbytheuseofglyphosate,whichusually successfullykillsoffthemajorityofindividuals.ifthissuddendie)offisn tfollowedbya removalofallofthestandinglitter,lightlevelsmightstillbelowenoughtoimpedethe colonizationofmoredesirablewetlandplantsuntilstandingdeadbiomassdecomposes, whichcantakeseveralyears.farrerandgoldberg(2009)alsofoundthatshadingeffects fromt. glaucalitterdecreasedtheabundanceanddiversityofnativespecies.gordon (1998)foundthattheabilitytoshadenativecompetitorswasacommonalityamong invasivespeciesinflorida. Thetemperaturedataloggersallowedmetocaptureseasonalvariationin temperature.datafromthehobodataloggersshowedthatthelargesttemperature differenceamongtreatmentswasatthesoilsurfacewheretotalremovalandlitterremoval plotshadthelargesttemperaturedifferencecomparedtoreferenceplots(figure3)10). ThistemperaturedifferenceamongtreatmentschangedatthebeginningofSeptemberto litterandtotalremovalplotshavingthelowesttemperatures,thoughbeforethebeginning 125

143 ofseptembertotalandlitterremovalplotsperiodicallyhadthelowestsoilsurfaceon relativelycooldays(lessthan~19 C).ThischangethatstartedinSeptemberwasnot predictedandcouldbeduealowercapacityfortotalandlitterremovalplotstoholdheat closetothesoilsurfaceduringperiodsofcoolingweatherand,thus,weremoredependent onincomingsolarradiationtomaintainhighsoilsurfacetemperatures.mackinney(1929) foundsimilareffectsofforestlitterontemperaturefluctuationsovermultipleseasons; litteractedlikeaninsulatorbydecreasingdailyhightemperaturesandincreasingdaily lows,andthiseffectdiminishedwithsoildepth.soiltemperaturesat2and10cmdepths showedthattotalremovalplotsweretheonlymanipulatedplotsthathadtemperatures differentfromreferenceplots,thoughthisdifferencewasmuchreducedafterseptember (Figures3)10and3)11).Thesedatasuggestthatlitterplaysasubstantialroleinthe temperatureregulationofthesoilandtheseeffectsarelikelytobegreaterwithhighlitter producingspeciessuchasphragmites. Thesignificanttreatmenteffectsonporewaterchemistrylikelyarefromthedirect effectofphragmites.concentrationsofna + andcl ) werelowerinthebiomassremoval plotscomparedtothereferenceplots,whichcouldbeindicativeofreducedevaporative concentrationbyevapotranspiration.asimilarpatternofincreasedsalinityduetoplant transpirationwasfoundinmangrovepopulationsinfrenchguiana(marchandetal.2004), andspartina+alternifloraisknowntoaltertheconcentrationofna +,Cl ),andothersaltsdue toionexclusionandsecretionwhengrowinginbrackishwaters(bradleyandmorris 1991).ThesamemechanismcouldalsocausethelowerconcentrationsofCa 2+ inthe biomassremovalplots,thoughwhytherewerealsodecreasedca 2+ concentrationsinthe 126

144 litterremovalplotsislessapparent.similarly,thesignificant,albeitweak,patternoflower nitrateconcentrationsinthereferenceplotscouldbeexplainedbydirectplantuptake, thoughnitrateconcentrationswerenotlowerinthelitterremovalplotwherelivebiomass remained.findlayetal.(2003)showedthatnitrateinporewaterwasn taffectedbythe presenceoflivingphragmites,thoughammoniumdidincreasewiththeremovalof Phragmites. Thelackofanytreatmenteffectsonlitterbagdecomposition,Nmineralization, nitrification,anddenitrificationwassurprising,especiallybecausethereweresignificant treatmenteffectsonlightlevelsandsoiltemperatures.withanincreaseinlightlevels,and subsequentsoiltemperatures,in+situlitterbagdecompositionandnetnmineralization ratesshouldhaveincreasedduetothetemperaturesensitivityoftheseecosystem processes.forin+situnmineralization/nitrificationrates,onepossiblecauseforthelackof treatmenteffectscouldhavebeenthatthesoilcoreswere10cmindepthandtreatment effectsonsoiltemperatureweregreaterclosertothesoilsurface,sousinga10cmcore couldhaveobscuredanytreatmenteffectpresentnearthesoilsurface.forthelitterbag assay,themajorityofthetime(~60ofthetotal90days)thelitterbagswereinthefield totalandlitterremovalplotshadlowertemperaturesthanreferenceplots,whichwas oppositeofwhatwaspredictedandlikelyledtothelackoftreatmenteffectson decompositionrates.potentialdenitrificationwasconductedinthelaboratoryfreefrom temperaturevariationexperiencedinthefield,sodifferencesindenitrificationpotential wouldhavebeenindicativeofeitherorganicmatterqualitychangesornitrateavailability, thoughnotreatmenteffectsweredetected.contrarytowhatifound,findlayetal.(2003) foundthatoneyearafterphragmitesremovalbyherbicide,potentialdenitrification 127

145 droppedby50%(comparedtolivingplots)andthisdecreasewaspossiblyduetothe cessationofoxygenreleasebytherootswhichallowedfornitrificationandtherefore nitrateneededfordenitrification.thebuildupofammoniumafterphragmitesremoval gavefurtherevidenceforthismechanism(findlayetal.2003). Whilenosignificanttreatmenteffectsweredetectedforanyecosystemprocessrate investigated,thereweresignificantsiteeffects.netnmineralizationrateswerethelowest atllp1whererateswerenegative(indicativeofnetnimmobilizationand/or denitrification),whileratesatglasbyandllp2werepositive(figure3)19).thebiggest differencebetweenllp1andtheothertwositeswasthelowpositionofthewatertable causingdrierconditions.likelyduetothemoreaerobicsoilconditions,nitratelevelswere higheratllp1thantheothertwosites,andammoniumconcentrationswerelow(table3) 1).ThenegativenetNmineralizationandnitrificationratesthereforecouldhavebeena consequenceofdenitrificationoccurringwithinthesealedsoilcoresinthefield,because whilellp1wasthedriestsite,itwaslikelystillmoistenoughtohaveanaerobicsoil microsites,whichhavebeenshowntobesitesofdenitrification(burginetal.2011). BecauseLLP1hadthegreateststartingnitrateconcentrationsandendedwiththelowest, nitrificationfollowedbydenitrificationisalikelyfateofremineralizedn.whilemicrobial NimmobilizationisanotherpossibilityforthenegativenetratesatLLP1,itisunlikely basedontheresultsfromchapters2and4thatshowedwhenincubatedinthelab,soil incubatedalonerarelyshowssignsofnimmobilization.thepositiverelationshipbetween soil%nandnetnmineralizationratesindicatesthatsoilswithmoren(likelyinorganic forms)haveagreaterpotentialformineralization(figure3)22)andhasbeenseenin similar+in+situnmineralizationassays(finzietal.1998). 128

146 TherewerenodeptheffectsonstemdecompositionatGlasbyorLLP1andrates werecomparablebetweensites.atllp2therewerestrongdeptheffectswithstem decompositionbeingthegreatestatthesoilsurface(figure3)26).onepossible explanationforthispatternisllp1andglasbywererelativelyconstantinwatertable positionoverthecourseoftheincubation,thoughtheactualwatertablepositionvaried considerablybetweensites;thewatertableatllp1wasbelowthesoilsurfaceandglasby hadconstantfloodedconditions.conversely,llp2 swatertablefluctuatedfromaboveto belowthesoilsurfacemultipletimesthroughouttheassayperiods,whichcouldhave createdidealconditionsfordecompositionasthewetting,drying,andrewettinglikely addedmoisture,nutrients,andaerobicconditions.jarvisetal.(2007)showedthatdrying andwettingconditionsincreaseddecompositionofmediterraneansoils,butthereisalso evidencethatinsomecasesawetting)dryingcycledoesn thavemucheffect(day1983) andthemagnitudeofeffectmaybegreaterforaridandsemiaridsoils(borkenandmatzner 2009).FilterpaperdecompositionwashigheronthesoilsurfaceatGlasbyandLLP2 comparedtollp1(figure3)27),whichcouldbeduetothosetwositeshavingperiodsof completeinundationthatdrovethebreakdownofthefilterpaperbybothphysicaland microbialmeans(increasedmicrobialcolonizationwhensubmergedinwater[glasbyand LLP2]comparedtowhenonarelativelydrysoilsurface[LLP1])(Day1983).Thehigher decompositionratesforfilterpapercomparedtostemtissueshowstherecalcitrantnature ofthestemtissueandthehighorganicmatterbuildupseeninphragmitesstandsatteststo this:themorelabileleavesdecomposequicklywhiletherecalcitrantstemsbuildupinthe soil(kominkovaetal.2000;agoston)szaboanddinka2008). 129

147 TheabsenceofpotentialdenitrificationatGlasbyisprobablyduetothelownitrate levelsinthesoil(figure3)28;findlayetal.2003;reddyanddelaune2008),whichis likelycausedbypreviousdenitrificationthatalreadyremovednitratefromthesoil/water column.also,thesoilc:nratiowasthehighestatglasbycomparedtollp1andllp2 (Table3)1)andsoilorganicmatterqualityhasbeenshowntoinfluencedenitrification rates(burfordandbremner1975;reddyanddelaune2008).themostconsistentlyhigh ratesofdenitrificationwerefromllp2andcan,asforthenmineralizationrates,be attributedtothefluctuatingpositionofthewatertablethatcreatedanidealenvironment forthealternationbetweennitrificationanddenitrification(mcclainetal.2003;jacintheet al.2012).themultipleregressionanalysisshowingnitrateconcentrationandsoilc:nratio assignificantpredictorsofdenitrificationfurthersupportsthisexplanationforthelow denitrificationratesatglasby,asglasbyhadbothlownitrateconcentrationsandlowsoil quality. Takentogether,thesignificanteffectsofsiteonlitterbagdecomposition,N mineralization/nitrification,anddenitrification,alongwiththedifferencesinsoil characteristicsamongsites,suggeststhestronginfluencesitedifferencescanhaveon wetlandbiogeochemicalcycling,evenwithinmonospecificstandsofthesameplant species.themostconspicuousdifferenceamongsiteswastheirhydrology.the differencesinhydrologyamongsiteslikelyinfluencedthedifferencesseenin biogeochemicalprocessrates,nutrientavailability(particularlynitrate),soilmoisture,soil organicmatter,andpossiblythedepthofthebelowgroundbiomassplacementof Phragmites(Table3)1).Changesinhydrologyhavebeenshowntoalteralmostevery aspectofthephysicalandchemicalnatureofwetlands(labaugh1986;vandervalk2000). 130

148 TheBGBdifferencesseenamongsites(highestatGlasbyandLLP2,comparedto LLP1)unlikelydemonstratesatruedifferenceinBGBproductionbecauseAGBwas comparableamongsites,andprobablysuggestsphragmitesplacesmostofitsbgbcloseto thesoilsurfaceinconsistentlywaterloggedsystemstoavoidanaerobicsoilconditions.at LLP1,wherethewatertablewasconsistentlybelowthesoilsurface,Phragmiteswaslikely toextenditsbgbwellbelowthetop30cmofsoiltoscavengeformorenutrientswithout havingthenegativeeffectsofanaerobiosis.thisbehaviorhasbeenseeninotherplants;for example,schwintzerandlancelle(1983)showedtherootingdepthandrootmorphology ofmyrica+gale,ashrubfoundinpeatlands,wasdependentonthedepthofthewatertable withrootsgrowingmorehorizontallythecloserthewatertablewastothesoilsurface. Futurestudiesshouldfurtherexaminetheeffectsoffloodingregimeon biogeochemicalcyclingwithinphragmitesstands,alongwiththemoredirecteffectsof floodingregimeontheplasticityofphragmites.additionally,thisstudyonlylookedat biogeochemistrywithinphragmitesstands,butshouldbeexpandedtoincludeother dominantwetlandspeciestodeterminespeciesidentitymattersonthehydrologyeffects seeninthisinvestigation.someoftheexpectedeffectsoflivingbiomassandlitterof PhragmitesonCandNcyclingwerenotseeninthisstudy,whichwaslikelyaconsequence oftherelativelyshorttimespanofthestudy.replicatingthisstudyoveralongertime scale,e.g.,5)15years,wouldallowformoregradualeffects,suchaschangesinsoilom qualityandquantity,tooccur.itislikelythatlongerstudieswouldfindthatliving PhragmitesisintegraltomaintaininghighsoilOMmattercontentusuallyseenunder monospecificstandsbycontinualinputsoflitterandsignificantsoilshadingthatdecreases OMdecomposition. 131

149 Chapter(4( Effects(of(Litter(Quality,(Soil(Origin,(and(Plant(Species(Diversity(on(Decomposition(in( Temperate(Wetlands( Brief(Rationale( Thechemicalandphysicalcharacteristicsofplantlitterhavebeenshowntoinfluence ecosystemprocessesinmanyenvironments(melilloetal.1982;mcclaughertyetal.1985; D AntonioandVitousek1992;Cornwelletal.2008),andthisbecomesespeciallyapparent whenaninvasiveplantbecomesabundantinanewenvironment.forexample,invasionof Bromus+tectorum+(cheatgrass)intothearidgrasslandsoftheColoradoPlateau(USA) decreasednmineralizationratesduetothesignificantlygreaterc:nratiooflitterinputs fromb.+tectorumcomparedtonativespecies(evansetal.2001).species)specificlitter quality(c:n,lignin:n,etc.)caninfluencecandncyclingbycontrollingdecompositionrates (Ehrenfeld2003;EvinerandChapin2003;Eviner2004;Orwinetal.2008).Myrica+faya,a nitrogen)fixerthatinvadedyoungvolcanicsitesonhawaii,wasshowntoenhancen cyclingbyproducingn)richlitterthatdecomposedquicklyreleasingplantavailablen (Vitouseketal.1987).Species)specificdifferencesinlitterqualityisapotentially importantaspectofinvasionsbyexoticplantsinwetlandsbecauseoftentheinvasive speciesbecomesdominantoverallotherspecies.invasivespeciescanalsoinvadeinto monospecificstandsofotherinvasivespecies,thoughtheeffectsofthistypeofinvasionon biogeochemicalcyclingislargelyunknown Toseparatespecies)specificlitterqualityfromothercontrolsondecompositionandN transformationrates,iperformedalaboratoryincubationusingbothlitterandsurficialsoil fromwetlandswithnearlymonospecificstandsofthreewidespreadinvasivewetland plants,phalaris+arundinacea,phragmites+australis,andtypha+ glauca(hereafterphalaris, 132

150 Phragmites,andTypha,respectively),aswellasfromanadditionalwetland+dominatedby+ Carex+lacustris(anativesedge;hereafterCarex).Thesedge)dominatedwetlandrepresents acommunitythathasnotbeeninvadedandhenceservedasareferencerelativetoinvaded plots.allfourstudyspeciesareinthesamefunctionalgroup(clonal,emergentwetland dominants;boutinandkeddy1993),soifsignificantdifferencesarefoundamongspecies thismightsuggestthatinvasionscanaltercarboncyclingeveniftheplantsaresimilarin growthform. Additionally,fewstudieshavetriedtodetermineifdominantplantspeciesinvoke strongsoillegacyeffects(termed soilorigineffects inthisstudy)thatcaninfluencethe decompositionoforganicmatterinputs.soilorigineffectscanhavesignificantinfluences oncandncyclingindependentofthecharacteristicsofthelitterinputsorclimate.the mechanismsofsoilorigineffectscanrangefromdifferencesinsoilmicrobialcommunityto nutrientavailabilitytoorganicmattercontent.forexample,soilmicrobialcommunities canbeadaptedtotheparticularphysicalandchemicalcharacteristicsofthelittertheyare accustomedtodecomposing(gholzetal.2000;stricklandetal.2009).thishasbeen referredtoas home)fieldadvantage (Ayresetal.2009)andusuallyresultsinhigher decompositionratesofresidentlitter.ifdominantplantspeciesfromthesamefunctional groupcaninfluencecandncyclingbyspecies)specificlitterandsoilorigineffects,then theremightbelessjustificationforcategorizingwetlandspecies,especiallyinvasive species,intogeneralizedfunctionalgroups. Whiletheincubationbrieflyexplainedaboveexploredtheeffectsoflitteridentityand soilsourceoncandnmineralization,ialsowasinterestedintheeffectsoflitterdiversity oncandnmineralization.forthis,iconductedasecondincubationexperimentinwhichi 133

151 mixeddifferentcombinationsoflitterfromthefourspeciesdescribedaboveintoa commonsoil.litterdiversityhasbeenshowntoenhancedecompositioninsome experiments,buttheoutcomesofmixingarenotalwayspredictablefromsinglespecies littertreatments(blairetal.1990;hectoretal.2000).understandingtheconsequenceof litterdiversityisimportantbecauseinvasivespeciesoftenbecomedominantbutmayor maynotformmonospecificstands.inmostcases,plantinvasiondecreasesthediversityof litterinputstosoilsystemsduetoadecreaseinplantspeciesdiversity.iflitterdiversity werecorrelatedwithdecompositionrates,thenoneoutcomeofmonospecificstand formation(andhenceasinglespecieslitterlayer)wouldbeareductioninoverall decompositionandanincreaseinorganicmatterbuildup.inotherwords,invasivespecies woulddecreasedecompositionrateswhentheyreducespecies(litter)diversity. Objectives,(Hypotheses,(and(Predictions( Objective)1:(Toseparatespecies)specificlitterqualityfromothercontrolsonCandN mineralizationratesandtodetermineifdominantwetlandspecies condition soil substrate. Hypothesis)1:(CandNmineralizationrateswilldependnotonlyonthespecies)specific qualityofthelitter(highquality=highmineralizationrates),butalsoontheconditioning ofthesoilbythedominantspecies(significantsoileffect).asaresult,ipredict: 1. Thefourstudyspecieswillvaryinlitterquality(C:Nratio)withPhragmiteslitter beingthemostrecalcitrant(higherc:nratio)andcarex+theleast(lowerc:nratio) 134

152 2. TherewillbeanegativerelationshipbetweenlitterC:NratiosandCandN mineralizationrates 3. AfterbackgroundsoilCmineralizationrates(basedonsoilemissionsofCO2without addedlitter)arefactoredoutoftotalcmineralization(soil+littercmineralization), therewillstillbeasignificantsoileffect,indicatingasoilorigineffect. Objective)2:TodetermineifwetlandspecieslitterdiversityinfluencesCandN mineralization.thisisanimportantcomponentofthebiogeochemicalimplicationsof invasionsbecausetheinitialstagesofinvasionshouldresultinadiverselitterlayer,withc andncyclingfeedbackspotentiallyaffectingtheabilityoftheinvadertobecomedominant. Hypothesis)2:Mixturesoflitterfromdifferentdominantwetlandspecieswillhavehigher decompositionratescomparedtosinglelittertypeadditionsduetohighersubstrate diversity.asaresult,ipredict: 1. TherewillbeapositiverelationshipbetweenlitterdiversityandcumulativeC mineralization. 2. Species)specificlitterdecompositionratesinsinglelittertreatmentswillpredict whichlitterdiversitytreatmentswilldecomposethefastest,e.g.,thetwospecies withhighestdecompositionratesinsinglelittertreatmentswillresultinthehighest decompositionrateswhenincubatedtogether. ( ( 135

153 Methods( Litter+quality+and+soil+origin+incubation+ Thelaboratoryincubationwassetupasa4x5factorialtreatmentdesignandwas conductedfrom23aprilto29june2010.foursoiloriginfactorlevelswerecrossedwith fivefactorlevelsofspecies)specificlitterforatotalof20treatmentcombinations.thefour soiloriginlevelsweresoilcollectedwithinmonospecificstandsofphalaris,phragmites, Typha,andCarex.Thespecies)specificlitterlevelswerethesamefourspeciesasthesoil originfactorwiththeadditionofanolitteradditionfactorlevel.eachtreatment combinationwasreplicatedsixtimesforatotal120experimentalsubjects(120incubation jars=4soiloriginlevelsx5litterlevelsx6replicates).thefactorialdesignenabledthe detectionofinteractionsbetweensoiloriginandspecies)specificlitter,aswellasthe influenceofsoiloriginidentityonlitterdecomposition. Sitedescriptionandsampleprocessing SoilandlittersamplesusedforthislaboratoryincubationwerecollectedfromLake LansingParkNorth(LLP)(42 o N85 o W),Haslett,MI.LakeLansingParkNorth isembeddedinamosaicoflakes,woodlots,andresidentialareas.thetotalareaofthe parkis166hectaresandconsistsmainlyofdeciduousforest,coniferousforest,andalarge interconnectedwetlandcomplexofapproximately70hectares.theparkhasbeen extensivelyinvadedbyavarietyofinvasiveplantspecies,includingphalaris,phragmites, andtypha.thewetlandcomplexhasbecomeamosaicofmonospecificstandsofthese threespecies,thoughsomeareasaremixturesofthesethreeinvasivespeciesalongwith somenativespecies.someofthemoreconspicuousnativespeciesincludecarexspp., 136

154 Juncusspp.,Sambucus+canadensis,Leersia+oryzoides,Eutrochiumspp.,Asclepias+incarnata, Echinocystis+lobata,andImpatiens+capensis.Litterwascollectedfrommonospecificstands ofthefourstudyspecies,phalaris,typha,phragmites,andcarex+(figure4)1),duringthefall of2009afterallplantshadsenesced,butbeforethefirstsnowfalltoavoidleaching.carex, anativesedge,wasusedinthisexperimentbecauseithasatendencytoformmonospecific standssimilartotheinvasiveplantspeciesinthisstudyandthusallowedforthe comparisonbetweennativeandinvasivespecieswithsimilargrowthhabits.each monospecificstandwasgreaterthan200m 2 andatleast90%ofthespeciescoverwasof thestudyspecies.eachmonospecificstandhadsimilarhydrology:earlyspringrainwould raisewaterlevelstoamaximum(<1maboveground),andbytheendofthegrowing seasonthewaterlevelwasbelowthesoilsurface. Withineachmonospecificstand,freshspecies)specificlitter(recentlysenescedand fallen)wascollectedwithinsix1)m 2 plotsusinglineartransectsamplingwith2.5meters betweeneachplot.inspring2010,six10)cmdeepcores(166cm 3 )werecollecteddirectly adjacentfromeachlittersamplingplotandsealedinwhirl)pakplasticbags(nasco), immediatelyplacedonice,andtransportedtothelaboratorywheretheywerekeptat4 C for2daysuntilthestartoftheincubation. Afterbeingstoredat4 Cfor2days,Isieved(4mm)eachcoretoremovelargeroots androcks.eachsoilcorewasthensub)sampledforbulkdensityand%moisture determination(60g),aswellasforinitialnitrateandammoniumconcentration determination(15g,seebelowfornmineralization/nitrificationmethods).thedrymass ofthe60gsub)samplewasmeasuredafterovendryingat80 Cfor48hours.Driedsoils 137

155 werethengroundandhomogenizedusingamortalandpestleandrunonanelemental combustionsystem(costechecs4010,valencia,ca)for%cand%nanalysis.samples wereruninduplicatewithatropineusedasastandardevery10samples.theremaining wetsoilwasthensplitintofivesubsamplesof20gandeachsubsamplewasplacedintoa 250mLincubationjar(ChromatographicSpecialties,Inc.;Ontario,Canada).These incubationsoilswereequilibratedfor7daysat4 Cpriortolittertreatmentadditionto allowthecmineralizationpulsefromrootdeathtopass.soilc:nratiosareexpressedona massbasis. Littercollectedateachmonospecificstandwasairdriedatroomtemperatureand storedfor6monthsbeforeprocessing.alllittersamplestakenfromaspecies)specific monospecificstandwerecombinedandmixedtohomogenizelittercharacteristics.litter wasthenseparatedbyorgan(stems,leaves,andinflorescences).species)specificorgan subsampleswerethencutbyhandandsievedthrougha4)and2)mmmesh.the2to4mm litterpieceswereusedintheexperimenttoensurecontactwiththesoilwithineach incubationjar.foreachspecies litter,multiplesubsamplesweretakenfromthe homogenizedmixtureforchemicalanalysis.litter%cand%nweredeterminedonan elementalcombustionsystem(seeabove)andc:nratiosareexpressedonamassbasis. Foreachreplicateofeachtreatmentcombination,onegramoflitter(1:1ratioof stemstoleaves)washandmixedintothesoiltomaximizephysicalcontactbetweensoil andlitter.jarswerethenallowedtoequilibratefor3daysandweresealedwithlidsfitted withseptatoallowroomairtoenterthejaruntilthestartofaco2samplinground(see below).alljars(120total)wereincubatedinthedarkfor68days.similarsoilmoisture conditionswerecreatedacrossallincubationsamplesbybringingeachtocomparable 138

156 moisturecontentsbeforethebeginningoftheexperiment(40)60%representingidealnon) limitingconditions).moisturecontentwasmaintainedweeklyoverthecourseofthe incubationbyaddinganappropriatevolumeofdistilledwateraftereachjarwasweighed todeterminewaterloss. Carbonmineralizationassay Carbonmineralizationrateswereestimatedduringseven24)hourperiodsoverthe 68)dayincubation(days1,4,8,13,26,41,and68).Duringeachperiod,a10mLheadspace gassamplewastakenfromeachjarimmediatelyafterjarsweresealed(time=0)usinga three)waystopcock)fittedsyringe,andthenafter6,12,and24hours.beforegassamples wereextracted,eachjarwasshakenbyhandtomixsoilporespacesandtoreleasetrapped gasbubbles.afterheadspacesampleswerecollected,jarswerebackfilledwith10mlofn2 gastoensureconstantairpressureandvolume.aftereachround,lidswereremoved, samplesweregentlyflushedwithambientair,andjarswerewrappedwithplasticwrapto preventmoistureloss. TheheadspacegassampleswereanalyzedforCO2concentrationsbyinjectingthe 10mLsampleintoaPP)systemEGM)4infraredgasanalyzer(IRGA).TheIRGAwas standardizedusingaco2standardgasafterevery20injections.carbondioxide concentrationswerecorrectedforheadspacedilutioncausedbybackfillingwithn2gas. TheslopeofCO2concentrationsovertheincubationperiodwasusedtocalculateC mineralizationrates.noslopehadanr 2 valueoflessthan0.85andthemajority(>95%) 139

157 weregreaterthan0.95.co2productionwasassumedtobeduetocmineralization (decomposition). TheCmineralizationratesforlitteradditiontreatmentswerebackground)corrected basedonco2productioninnolittertreatmentcounterparts(assumedtorepresent ambientsoilcmineralization)fortheparticulardayofmeasurement,andthendividedby litterdryweighttoreportdataonamassbasis(gco2)ckg )1 littercday )1 ).Firstorder rateconstants(k,day )1 )werecalculatedbytakingthenaturallog(in)ofthec mineralizationratesandthendeterminingtheslopeoftheintransformedratesoverthe timecourseoftheincubation.totalco2productionwascalculatedbyfittinganonlinear curve(log)tothetimecourseofratesdescribedabove,theninterpolatingdailyco2 productionandsummingthesevalues. Nmineralization/nitrificationassay InitialNO3 ) andnh4 + concentrationsweredeterminedfromthe15gsubsample collectedatthetimeofinitialsoilprocessingusingthekclextractionmethod(robertson 1999).Afterthe68)dayincubationperiod,thecontentsofeachjar(litterandsoil)were extractedforfinalno3 ) andnh4 + concentrationsusingthesamemethod.concentrations ofno3 ) andnh4 + intheextractswereanalyzedbythemicroplatemethodusingprotocols developedbydr.davidrothstein(dept.offorestry,msu).netratesofnmineralization andnitrificationwerecalculatedfromthechangesininorganicn(nh4 + +NO3 ) )orno3 ), 140

158 respectively,duringtheincubationperiod(initial finalpoolsizes/incubationperiod).n mineralizationandnitrificationrateswereexpressedonasoilmassbasissimilartothec mineralizationcomponentoftheexperiment. Litter+diversity+incubation+ Thelitterdiversityincubationwasdesignedasasinglefactortreatmentstructure andwasconductedfrom1december2010to24january2011.thesinglefactorof species)specificlitterdiversityconsistedof16factorlevelsofdifferentcombinationsof littercollectedfrommonospecificstandsofphalaris,phragmites,typha,andcarex.the16 treatmentlevelsconsistedofallpossiblespeciescombinationswithinalitterdiversitylevel andwereasfollows:singlespecies(4),twospecies(6),threespecies(4),allspecies(1)and nolitter(1).areplacementdesign(asopposedtoanadditivedesign)wasusedforlitter mixtures(seebelow).alllittertreatmentlevelswereincubatedina commonsoil, meaningthesoilwasnotcollectedfromamonospecificstandofanyofthefourspecies. Instead,thesoilwascollectedfromashallow,unvegetatedephemeralpondtominimize thepossibleconditioningeffectsplantspeciescouldhaveonthesoil.eachtreatmentlevel wasreplicatedseventimesforatotal112experimentalsubjects(incubationjars).this experimentaldesignwasdevelopedtotesttheeffectsofwetlandspecieslitterdiversityon CandNtransformationrates. Sitedescriptionandsampleprocessing SoilandlittersamplesusedforthislaboratoryincubationwerecollectedfromLake LansingParkNorth,withinthesamewetlandcomplexusedforthesoiloriginincubation 141

159 describedabove(figure4)1).litterwascollectedusingthesameprotocolandfromthe samemonospecificstandsofthefourstudyspeciesasinthesoiloriginincubation.during thefallof2010,litterwascollectedafterallplantshadsenesced,butbeforethefirst snowfalltoavoidleaching.withinaunvegetatedephemeralwetland,twenty10)cmdeep soilcores(166cm 3 )werecollectedduringfall2010usinglineartransectsamplingwith onemeterbetweeneachcore.thesesoilcoresweresealedinwhirl)pakbags(nasco), immediatelyplacedonice,andtransportedtothelaboratorywheretheywerekeptat4 C for2daysuntilthestartoftheincubation. Afterbeingstoredat4 Cfor2days,eachcorewassieved(4mm)toremovelarge rootsandrocks.eachsievedsoilcorewasthencombinedandhomogenizedinalarge plasticcontainer.eighteensub)samples(30g)weretakenforbulkdensityand%moisture determination,andeighteenmoresubsamplesweretakenforinitialnitrateand ammoniumconcentrationdetermination(15g,seebelowfornmineralization/nitrification methods).thedrymassoftheeighteen30gsub)sampleswasmeasuredbyovendryingat 80 Cfor48hours.Driedsoilswerethengroundandhomogenizedusingamortaland pestleandrunonanelementalcombustionsystem(costechecs4010,valencia,ca)for %Cand%Nanalysis.Sampleswereruninduplicatewithatropineusedasastandard every10samples.fromthehomogenizedwetsoil,11230)gsubsampleswereplacedinto separate250mlincubationjars(chromatographicspecialties,inc.;ontario,canada). Theseincubationsoilswereequilibratedfor7daysat4 Cpriortolittertreatmentaddition toallowthecmineralizationpulsefromrootdeathtopass.littercollectedateach monospecificstandwasairdriedatroomtemperaturefortwoweeksbeforeprocessing. Litter%Cand%Nweredeterminedonanelementalcombustionsystem,while%lignin 142

160 wasdeterminedbynearinfraredreflectancespectrophotometry(samplesanalyzedby LitchfieldAnalyticalServices,MI;McLellanetal1991). Theremaininglitterprocessingwascarriedoutasinsoiloriginincubation.For eachreplicateofeachtreatmentlevel,2goflitterwashandmixedintothecommonsoilto maximizephysicalcontactbetweensoilandlitter.asmentionedabove,litterwasadded withinareplacementdesign,asopposedtoanadditivedesign.thesametotalamountof litterwasaddedtoeachincubationjarregardlessoflitterdiversitytreatment,e.g.,2gof Phragmiteslitterwasaddedforthesinglespeciesadditions,butforthetwospecieslitter additionofphragmitesandphalaris,1gofeachwasadded.areplacementdesignwasused tokeepthetotalamountoflitterthesamebecausechangingtheamountoftotallitter addedwouldalterthedecompositionratesandwouldconfoundanydiversityeffects.the stem:leafratioofaddedlitterdifferedamongspecies(3:1ratioforphalarisandphragmites and1:1ratiofortyphaandcarex)inthisexperimenttoapproximatestem:leafratiosthat occurinthefield.jarswerethenallowedtoequilibratefor3daysafterwhichtheywere looselysealedwithlids(fittedwithsepta)toallowroomairtoenterthejaruntilthestart ofaco2extractionround(seebelow).alljars(112total)wereincubatedinthedarkfor 55days.Non)limitingsoilmoistureconditionswerecreatedsimilartothesoilorigin incubation. Carbonmineralizationassay Carbonmineralizationrateswereestimatedduringsix24)hourperiodsoverthe55) dayincubation(days1,3,7,15,29,and55).iestimatedco2productionandc 143

161 mineralizationratesfollowingthesamemethodsasoutlinedinincubation1(litterquality andsoiloriginincubation).noslopehadanr 2 valueoflessthan0.85andthemajority (>95%)weregreaterthan0.90.TheCmineralizationratesforlitteradditiontreatments werebackground)correctedbasedonthenolittertreatmentforaparticulardayof measurementandthendividedbylitterdryweighttoreportdataonamassbasis(gco2)c kg )1 littercday )1 ).Firstorderrateconstants(k,day )1 )andtotalco2productionwere calculatedasinthesoiloriginincubation. Nmineralization/nitrificationassay InitialNO3 ) andnh4 + concentrationsweredeterminedfromthe15gsubsample collectedatthetimeofinitialsoilprocessingusingthekclextractionmethod(robertson 1999).Afterthe55)dayincubationperiod,thecontentsofeachjar(litterandsoil)were extractedforfinalno3 ) andnh4 + concentrationsusingthesamemethod.concentrations ofno3 ) andnh4 + intheextractswereanalyzedbythemicroplatemethodusingprotocols developedbydr.davidrothstein(dept.offorestry,msu).netratesofnmineralization andnitrificationwerecalculatedfromthechangesininorganicn(nh4 + +NO3 ) )orno3 ), respectively,duringtheincubationperiod(initial finalpoolsizes/incubationperiod).n mineralizationandnitrificationrateswerecalculatedonasoilmassandsoilcarbonbasis similartothecmineralizationcomponentoftheexperiment. 144

162 Statistical+analysis+ Generallinearmodels(GLMs)wereusedtotestfortreatmenteffectsonfirstorder rateconstants,totalcmineralization,nmineralization,andnitrification.specieseffectson soil%c,%n,andc:nratioandlitterchemistry(%c,%n,c:nratio,%lignin,lignin:nratio) weredeterminedusingglms.tukey shsdmultiplecomparisontestswereperformedto determinesignificantdifferencesbetweenfactorlevels.todeterminetherelationship betweenlitterdiversityandtotalcmineralization,aregressionanalyseswasperformed withlitterdiversitytreatments1though4astheindependentfactor.simplelinear regressionwasusedtoinvestigatebothsoilandlitterqualitycontrolsoncandn mineralizationrates.modeldiagnosticswereassessedforeachanalysistodetermineifthe residualswerenormallydistributedanddisplayedconstanterrorvariances.log transformationswereusedtocorrectforanyheteroscedasticity.allstatisticaltestswere performedinr2.13.2(rdevelopmentcoreteam2011). 145

163 km ± Lake Lansing Pha Typ [_ [_ [_ Phr [_ Car Figure4)1.MapshowingthelocationofthemonospecificstandsofPhragmites+australis+ (Phr),+Phalaris+arundinacea+(Pha),+Typha glauca+(typ),+and+carex+lacustris(car)inthe wetlandareawithinlakelansingparknorth,haslett,mi. ( ( ( 146

164 Results( Litter+quality+and+soil+origin+incubation+ Firstorderrateconstants(k,decompositionrate)variedamongtreatment combinations,withthehighestrateconstantoccurringwhenphragmiteslitterwas incubatedinphalarissoil(0.0282±0.012day )1 )andthelowestwhentyphalitterwas incubatedin+carexsoil(0.0085±0.003day )1 )(Table4)1).Foraspecies)specificlittertype, therewasageneralpatternofthehighestdecompositionrateoccurringwhenincubatedin Phragmitessoil,followedbyPhalaris,Typha,andCarex,exceptforPhragmiteslitterwhich showednopatternamongthesoilitwasincubatedin(marginallitterxsoilinteraction;p= 0.068).Averagedoversoilorigin,Phragmiteslitterhadthehighestdecompositionrateand Typha+litterthelowest(maineffectoflitter;p<0.001;Table4)2).Theonlytreatment combinationthathadacomparabledecompositionratecomparedtophragmiteslitterwas PhalarislitterwhenincubatedinPhragmitessoil.Whendecompositionrateswere averagedoverspecies)specificlittertype,carexsoilhadthelowestandphragmitessoilthe highest(maineffectofsoilorigin;p<0.001;table4)2) PhragmitesandPhalarislitterhadthehighesttotalcarbonmineralizationrates(C) min),followedbycarexandthentyphawhenaveragedacrosssoilorigin(figure4)2; significantmaineffectoflitter;p<0.001;table4)2).whenaveragedacrossspecies) specificlitter,soilcollectedundermonospecificstandsoftyphaandcarexhadthegreatest totalc)min,followedbyphalarisandthenphragmites(figure4)2;significantmaineffectof soilorigin;p<0.001;table4)2).overall,thetreatmentcombinationthatyieldedthe highestc)minwasphalarislitterincubatedwithtyphasoil,whereastyphalitterincubated 147

165 withphragmitessoilyieldedthelowestc)min.theinteractionbetweenspecies)specific litterandsoiloriginwasnotsignificant.thesignificanteffectofsoiloriginontotalc)min afterbackgroundc)minattributedtosoilalonewasfactoredoutsuggeststheimportance ofsoilorigin. Thereweresignificantspecieseffectsonsoil%C,%N,andC:Nratio(Table4)3). PhragmitessoilhadthehighestsoilC:Nratio(significantmaineffectofspecies;p<0.001; Table4)3),indicatingthatthequalityofitssoilorganicmatterwaspoorercomparedto soilsofdifferentspeciesorigin,andthisisconsistentwithtotalc)minresultssuggesting Phragmitessoilorganicmatterwastheleastlabile.PhalarisandCarexsoilhad intermediatesoilc:nratioswithcarexsoilc:nratiossignificantlygreaterthanthatof+ Typha.SoilscollectedfrommonospecificstandsofPhalarisandTyphahadthehighestsoil %Cand%N,whilesoilscollectedfromPhragmitesandCarexhadthelowestC:Nratios,and forsoil%n,phragmiteshadsignificantlylessthancarex(significantspecieseffect;p< 0.001;Table4)3). LitterNcontentsignificantlydifferedamongspecies.TyphaandCarexlitterhadthe highestlitterc:nratiosat~65,followedbyphalarisat~40andphragmitesat~28 (significantspecieseffect;p<0.001;table4)3).forlitter%n,phragmiteslittercontained thegreatestamount,followedbyphalarisandthentyphaandcarex,whichwerenot significantlydifferentfromeachother(significantspecieseffect;p<0.001;table4)3).a differentpatternaroseforlitter%c;phalarisandtyphalitterhadthehighest%c,followed bycarexlitterandfinallyphragmites(significantspecieseffect;p<0.001;table4)3). PhragmiteslitterhadthelowestC:Nratiosduebothtothehighestlitter%Nandthelowest litter%camongallspecies. 148

166 PaststudieshaveshownthatsoilandlitterC:Nratio(indicatorsofquality)canhave significantcontrollingeffectsondecompositionrates(melilloetal.1982;tayloretal.1989, Berg2000).Totestthis,simplelinearregressionwasusedtodetermineifarelationship betweentotalc)minandeitherlitterorsoilc:nratioexisted.therewasnorelationship betweentotalc)minandsoilc:nratiowhenalltreatmentcombinationswereincludedin theanalysis(figure4)3;adjustedr 2 =0.003,p=0.423),norwasthisrelationship significantwhenalllitteradditiontreatmentcombinationswereremovedandonlyno Litteraddition(soilonly)treatmentswereanalyzed(Figure4)4;adjustedR 2 =0.077,p= 0.105).TherewasasignificantpositiverelationshipbetweentotalC)min(NoLitter treatmentsonly)andsoil%n(figure4)5;adjustedr 2 =0.192,p=0.018).Forlitter additiontreatments,litterc:nratiohadanegativerelationshipwithtotalc)min(figure4) 6;totalC)min;adjustedR 2 =0.524,p<0.001),thoughtherelationshipwasmuchstronger atthebeginningoftheincubation(figure4)7;day1c)min;adjustedr 2 =0.861,p<0.001). ThesedataindicatethattheinfluenceoflitterqualityonC)mindecreasedthroughoutthe incubation. NetNmineralizationandnitrificationrateswerealmostidenticaltoeachother becausethemajorityoftheammoniummineralizedwasnitrifiedtonitrate;thereforeonly netnmineralization(n)min)rateswillbediscussed.similartototalc)min,onlythemain effectsofsoiloriginandspecies)specificlitterweresignificant,nottheirinteraction(figure 4)8;p<0.001forboth;Table2).BothpositiveandnegativeN)minrateswerefound, indicatingnimmobilizationoccurredinsometreatmentcombinations(negativen)min rates).forthenolitteradditiontreatments,allsoil)origintreatmentlevelshadpositiven) 149

167 minrates,withphragmitesandtyphasoilhavingthehighestandphalarisandcarexhaving thelowestrates.phragmites+litterwastheonlylitteradditiontreatmentlevelthatresulted inpositiven)minratesforallsoilorigins(italsohadthelowestlitterc:nratio:figure4)8). AmongsoilsthatPhragmiteslitterwasincubatedin,PhragmitesandTyphasoilresultedin thehighestn)minrates,whilephalarisandcarexsoilresultedinthelowest.forother littertypes(phalaris,typha,andcarex)mostofthen)minrateswerenegative,exceptfor whenphalarislitterwasincubatedintyphasoil,whichresultedinpositivevaluesthat werecomparabletolowvaluesforphragmiteslitter.regressionanalysiswasusedto determinetherelationshipbetweenn)minratesandlitterc:nratioandasignificant negativecurvilinearrelationshipwasfound(figure4)9;r 2 =0.407,p<0.001).No significantrelationshipwasfoundforn)minratesandsoilc:nratio.theseresultssuggest, asforc)min,litterc:nratiopartiallycontrolledn)minrates. Litter+diversity+incubation+ Amongsinglespecieslitteradditiontreatments,Phragmiteslitterhadthelowest decompositionrateconstantandphalarislitterthehighest(treatmenteffect;p<0.001; Tables4)4and4)5).Forthedoublespecieslitteradditiontreatments,alllittermixtures thatincludedphragmiteslitterhadthelowestdecompositionratecomparedtoallother littercombinations.therewerenodifferencesamongtriplelitteradditionspecies mixtures,whichalsowerenotdifferentfromthenon)phragmitesdoublespecieslitter mixturesandtheallspecieslittermixture. 150

168 TotalC)minvariedamonglitteradditiontreatments(overallmean:271gCO2)Ckg )1 litterc)withthegreatestdifferencebeingbetweentyphalitteradditionandphragmites+ Phalarislitteraddition(Figure4)10;significanttreatmentmaineffect;p<0.001;Table4) 5).SingleormultiplespeciesadditionsthatincludedTyphalitterhadthelowesttotalC) min,whilelittermixturesthatincludedphalarisusuallyhadthehighesttotalc)min.for thesinglelitteradditiontreatments,carexlitterhadthegreatesttotalc)minandtypha littertheleast.thetreatmentwiththegreatesttotalc)minwasthetwospecieslitter additionofphragmitesandphalaris,whichwassignificantlygreaterthanwheneitherof thesetwospecieswereincubatedalone,indicatingthepossibilityofanon)additive relationshipbetweenthesetwotypesoflitter.thoughtherewasnotastrongeffectof litterdiversityontotalc)min,therewasanobservabledecreaseinthevarianceoftotalc) minaslitterdiversityincreased. Soilusedinthisincubation,whichwascollectedfromtheephemeralpondatLLP, hada%cof23.29(±0.36),a%nof1.72(±0.03),andac:nratioof13.51(±0.09).litter C:Nratioswerehigheranddifferedamongspecies;PhalarisandTyphahadthehighestC:N ratioat~62.5andphragmiteshadthelowestc:nratioat47.2(significantspecieseffect;p <0.001;Table4)6).Percentligninandlignin:Nratiosfollowedasimilarpatternamong species.thehighest%ligninwasobservedintyphalitter,withcarexandphalarishaving thelowest%ligninandphragmites,phalaris,andcarexhavinglowerlignin:nratiothan Typha(significantspecieseffect;p<0.001;Table4)6). SimplelinearregressionanalysisfortotalC)minonlitterC:Nratiosshowedamuch weakernegativerelationshipthanforthelitterqualityandsoiloriginincubation,though therelationshipwasstillsignificant(figure4)11;adjustedr 2 =0.131,p<0.001).The 151

169 relationshipbetweentotalc)minand%ligninwassomewhatstronger(figure4)12; adjustedr 2 =0.228,p<0.001)andtherelationshipbetweentotalC)minandlignin:Nratio wasthebestfitamongallthelitterqualitypredictors(figure4)13;r 2 =0.313,p<0.001). LitterdiversitydidnothavealargeimpactontotalC)min,thoughtherelationshipwas significant(figure4)14;adjustedr 2 =0.075,p=0.002),andasmentionedbefore,there wasareductioninthevarianceoftotalc)minaslitterdiversityincreased. Aswiththelitterqualityandsoiloriginincubation,netNmineralizationrates mirrorednetnitrificationrates,therefore,onlyn)minrateswillbediscussed.theonly treatmentthathadpositiven)minrateswasthenolitteradditiontreatment,the remaininglitteradditiontreatmentlevelsallhadnegativen)minrates,indicatingnetn immobilization(figure4)15;significantlittertreatmenteffect;p<0.001;table4)5). ThoughtheNoLitteradditiontreatmentwassignificantlydifferentfromalllitteraddition treatmentlevels,noneofthelitteradditiontreatmentswerestatisticallydistinctfromthe rest.theconsistenttrendfornimmobilizationforeachlitteradditiontreatmentlevelcan beexplainedinthesamewayasthesoiloriginincubation,eventhoughthesamespecies) specificlitterwasusedinbothincubations. 152

170 Table4(1.Averagedecompositionratesexpressedasfirst(orderrateconstants(k;day (1 )foreachlitterx soilorigintreatmentcombination. SoilAddition LitterAddition Std. Std. Std. Std. Phragmites+ Error Phalaris+ Error Typha+ Error Carex+ Error Phragmites Phalaris Typha Carex

171 Table4(2.Summaryofthetwo(factorANOVAsfortheeffectofspecies( specificlitterandsoilondecompositionconstant(k),cumulativec mineralization,andnmineralization. Source numdf dendf F P>F K"constants" " Soil < Litter < SoilxLitter Cumulative"C" mineralization" " Soil < Litter < SoilxLitter N"Mineralization" " Soil < Litter < SoilxLitter

172 Table4(3.Soilandlitter%C,%N,andC:Nmassratiosofthefourspeciesusedinthelitterquality andsoiloriginincubation.samelettersuperscriptdenotesnonsignificantdifferencesaccordingto Tukeyposthoctests.Valuesaremeans±SE. Species Soil%C Soil%N SoilC:N Litter%C Litter%N LitterC:N Phragmites+ 24.8±1.07 a 1.78±0.10 a 14.0±0.32 a 41.4±0.15 a 1.48±0.01 a 28.0±0.32 a Phalaris ±0.39 b 3.10±0.03 b 13.0±0.08 b 45.6±0.14 b 1.14±0.03 b 40.0±0.94 b Typha ±3.62 b 3.13±0.28 b 12.4±0.17 c 45.5±0.18 c 0.62±0.01 b 74.3±1.37 c Carex ±1.09 c 2.37±0.09 c 13.1±0.07 b 43.1±0.16 c 0.62±0.01 c 69.8±1.51 c 155

173 Table4(4.Averagedecompositionratesexpressedasfirst(orderrateconstants(k; day (1 )foreachlitterdiversitytreatment. Litter Diversity Species kconstant(day (1 ) Standard Error 1 Phalaris( Typha( Phragmites( Carex( Phragmites(+(Phalaris( Phragmites(+Typha( Phragmites(+(Carex( Phalaris(+(Typha( Phalaris(+(Carex( Typha(+(Carex( Phragmites(+(Phalaris(+(Typha( Phragmites(+(Phalaris(+(Carex( Phragmites(+(Typha(+(Carex( Phalaris(+(Typha(+(Carex( AllSpeciesLitter Table4(5.SummaryofANOVAsfortheeffectofTreatmentondecomposition(K) constant,cumulativecmineralization,andnmineralization. Response numdf dendf F P>F KConstant CumulativeC mineralization < Nmineralization < Table4(6.LitterC:Nmassratios,%lignin,andlignin:N massratiosofthefourspeciesusedinthelitter diversityincubation.samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoc tests.valuesaremeans±se. Species C:N %Lignin Lignin:N Phragmites( 47.2±0.03 a 11.1±0.40 a 12.4±0.45 a Phalaris( 62.0±1.10 b 8.9±0.24 b 12.6±0.47 a Typha( 63.0±0.81 b 13.7±0.02 c 19.1±0.20 b Carex( 53.7±2.0 c 10.0±0.30 b 12.1±0.10 a 156

174 Total&C&Min&(g&CO 2 /C&kg /1 &li2er&c)& 800" 700" 600" 500" 400" 300" 200" a a a a b c a a d e e e e Phragmites"Soil" Phalaris"Soil" Typha"Soil" Carex"Soil" c bc b 100" 0" Phragmites" Phalaris" Typha" Carex" Species&Li2er& Figure4)2.MeancumulativeCmineralizationoverthe68)daylitterqualityandsoiloriginlaboratory incubation.themaineffectsofspecies)specificlitter(f3,80=69.43,p<0.001)andsoilorigin(f3,80=11.29,p< 0.001)weresignificant,butnottheirinteraction.Samelettersuperscriptdenotesnonsignificantdifferences accordingtotukeyposthoctests.errorbarsrepresent1se. 157

175 Total&C&Min&(g&CO 2 /C&g /1 &SC)&& 350" 300" 250" 200" 150" 100" 50" 0" 11.5" 12.5" 13.5" 14.5" 15.5" Soil&C:N&Ra6o& Figure4)3.RegressionbetweensoilC:NratioandcumulativeCmineralization(all treatments)(adjustedr 2 =0.003,p=0.423). Total&C&Min&(g&CO 2 /C&g /1 &SC)&& 80" 70" 60" 50" 40" 30" 20" 10" 0" 11.5" 12.5" 13.5" 14.5" 15.5" Soil&C:N&Ra6o& Figure4)4.RegressionbetweensoilC:NratioandcumulativeCmineralization(nolitter treatmentsonly)(adjustedr 2 =0.077,p=0.105). 158

176 Total&C&Min&(g&CO 2 /C&g /1 &SC)&& 80" 70" 60" 50" 40" 30" 20" 10" 0" 1" 1.5" 2" 2.5" 3" 3.5" 4" Soil&%N& Figure4)5.Regressionbetweensoil%NratioandcumulativeCmineralization(nolitter treatmentsonly)(adjustedr 2 =0.192,p=0.018). Total&C&Min&(g&CO 2 /C&&kg /1 &li9er&c)&& 900" 800" 700" 600" 500" 400" 300" 200" 100" 0" 22" 32" 42" 52" 62" 72" 82" Li9er&C:N&Ra6o& Figure4)6.RegressionbetweenlitterC:NratioandcumulativeCmineralization(litter additiontreatmentsonly)(adjustedr 2 =0.524,p<0.001). 159

177 Day&1&C&Min&(g&CO 2 /C&kg /1 &li9er&c)&& 40" 35" 30" 25" 20" 15" 10" 5" 0" 22" 32" 42" 52" 62" 72" 82" Li9er&C:N&Ra6o& Figure4)7.RegressionbetweenlitterC:Nratioandday1Cmineralization(Litteraddition treatmentsonly)(adjustedr 2 =0.861,p<0.001). 160

178 Net$N$Mineraliza,on$(mg$N$kg 21 $soil$day 21 )$ 7# 6# 5# 4# 3# 2# 1# 0# a b a b c cd b d c d c d Phragmites#Soil# Phalaris#Soil# Typha#Soil# Carex#Soil# c d d d a e a e 1# 2# Phragmites Phalaris Typha Carex No Litter Li9er$Type$ Figure4)8.MeannetNmineralizationoverthe68)daylitterqualityandsoiloriginlaboratoryincubation.Themain effectsofspecies)specificlitter(f3,100=92.30,p<0.001)andsoilorigin(f12,100=14.07,p<0.001)weresignificant, butnottheirinteraction.samelettersuperscriptdenotesnonsignificantdifferencesaccordingtotukeyposthoctests. Errorbarsrepresent1SE. 161

179 Net$N$Min$(mg$N$kg,1 $soil$day,1 )$ 8# 6# 4# 2# 0# 2# 4# 20# 30# 40# 50# 60# 70# 80# Li6er$C:N$Ra;o$ Figure4)9.RegressionbetweenlitterC:NratioandnetNmineralization(adjustedR 2 = 0.452,p<0.001). 162

180 163 Figure4)10.MeancumulativeCmineralizationoverthe55)daylitterdiversitylaboratoryincubation.Themain effectoflittertreatmentwassignificant(f14,90=8.08,p<0.001).samelettersuperscriptdenotes nonsignificantdifferencesaccordingtotukeyposthoctests.errorbarsrepresent1se. 0" 50" 100" 150" 200" 250" 300" 350" 400" Phalaris" Typha" Phragmites" Carex" Phrag"+"Phal" Phrag"+Typha" Phrag"+"Carex" Phal"+"Typha" Phal"+"Carex" Typha"+"Carex" Phrag"+"Phal"+"Typha" Phrag"+"Phal"+"Carex" Phrag"+"Typha"+"Carex" Phal"+"Typha"+"Carex" All"Species"Li=er" Total&C&Mineraliza.on&(g&CO 2 3C&kg 31 &li6er&c)& Li6er&Treatment& a b ab a c ab a b ab b ab ac ab ab ab