Carbon dioxide fluxes across the Sierra de Guadarrama, Spain

Transcription

1 Cron dioxide fluxes ross the Sierr de Gudrrm, Spin R. Inln C. Urie D. De L Torre D. M. Snhez M. A. Clvero A. M. Fernndez R. Mornte A. Crden M. Fernndez A. Ruio Astrt Understnding the sptil nd temporl vrition in soil respirtion within smll geogrphi res is essentil to urtely ssess the ron udget on glol sle. In this study, we investigted the ftors ontrolling soil respirtion in n ltitudinl grdient in southern Mediterrnen mixed pine-ok forest eosystem in the north fe of the Sierr de Gudrrm in Spin. Soil respirtion ws mesured in five Pinus sylvestris L. plots over period of 1 yer y mens of losed dynmi system (LI-COR 6400). Soil temperture nd wter ontent were mesured t the sme time s soil respirtion. Other soil physio-hemil nd miroiologil properties were mesured during the study. Mesured soil respirtion rnged from 6.8 to 1.4 jimol m -2 s _1, showing the highest vlues t plots situted t higher elevtion. gio vlues rnged etween 1.30 nd 2.04, while Ri 0 vlues rnged etween 2.0 nd 3.6. The results indite tht the sesonl vrition of soil respirtion ws minly ontrolled y soil temperture nd moisture. Among sites, soil ron nd nitrogen stoks regulte soil respirtion in ddition to soil temperture nd moisture. Our results suggest tht pplition of stndrd models to estimte soil respirtion for smll geogrphi res my not e dequte unless other ftors re onsidered in ddition to soil temperture. Keywords Soil respirtion Miroil iomss ron Cron nd nitrogen stoks Soil wter ontent Soil temperture Pinus sylvestris Altitudinl trnsets Introdution The hrteriztion of soil respirtion (SR) response through time nd spe is inresingly importnt to identify dominnt soures nd sinks of ron (C) nd prmeterize ron yling to represent forest-tmosphere intertions in glol modelling studios (Cox et l. 2000; Goh 2004). In the lst dede, mjor efforts hve een mde to understnd the environmentl drivers of soil respirtion. Soil temperture (ST) nd soil moisture (SM) explin most of the vrition in this prmeter (Dvidson et l. 1998; Rey et l. 2002), ut dditionl ftors suh s forest type, soil fertility, soil texture, stnd ge, plnt photo syntheti tivity nd topogrphy lso ffet soil respirtion in forested eosystems (Rodeghiero nd Cestti 2005; Dilustro et l. 2005; Tng et l. 2005; Kng et l. 2003). However, the identifition of the environmentl ftors ontrolling the vriility of SR still remins diffiult tsk surrounded y lrge unertinties, espeilly for forest soil in mountinous regions nd when it is neessry to onsider the effets of disturnes ssoited with forest fires. This is of mjor relevne in the Mediterrnen forest eosystems tht re highly vulnerle to limte hnge. Numerous studies long elevtion grdients indite tht soil C onentrtions or stoks inrese with ltitude in

2 mountinous terrins (Rodeghiero nd Cestti 2005; Grten nd Hnson 2006). Field studies in the mountins of more rid res indite tht soil moisture is n importnt ftor ontrolling soil C stoks nd fluxes in elevtion grdients (Wng et l. 2000; Li et l. 2007). Topogrphyindued mirolimtes n ffet SR rtes y onstrining mirolimti ftors, suh s soil temperture nd moisture (Kng et l. 2003; Li et l. 2007). Other studies suggest tht severl hemil nd iologil ftors suh s nitrogen (N) nd C dynmis o-vrying with soil moisture regulte the sptil distriution of soil C losses through deomposition (Grten nd Hnson 2006). The purpose of this study ws to investigte the min ftors tht ontrol sesonl nd sptil vrition of soil respirtion long n elevtion grdient in the northern fe of the Sierr de Gudrrm mountins (entrl Spin). Mterils nd methods Study site The study took ple in entrl Spin (Vlsin, Segovi), loted in the northern fe of the Sierr de Gudrrm (40 51'N, 4 3'W). The totl re of the Vlsin forest is h, overed minly y Sots pine {Pinus sylvestris L.). Other speies present inlude ok {Querus pyreni Willd.) nd montne room {Cytisus purgns (L.) Boiss.), with smll res of Holm ok {Querus ilex susp. llot (Desf.) Smp.) nd riprin forest. The hereous lyer is lrgely mde up of grsses, whih develop in spring, dry off in summer nd regrow to some extent fter the first utumn rins. The limte is nemoro-mediterrnen. The rinfll distriution is irregulr, with drought period in summer of pproximtely 2 months nd n nnul verge rinfll of 1,600-1,400 mm. Men tempertures rnge etween 1.5 nd 2.7 C during winter nd 19.7 nd 20.3 C during summer. Geologilly, grnites re predominnt. Soils re lssified s Humi Cmisols or Typi Hplumrepts. Experimentl design A trnset ws estlished in 64 h P. sylvestris L. wtershed spred long n elevtion grdient rnging from 1,320 to 1,592 m sl. Four smpling plots with dimensions 10 m x 15 m were designted within the experimentl site. An dditionl site (plot 100) ws seleted t higher elevtion (1,700 m sl), n re tht ws urned 2 yers previously (Tle 1). The tree density ws 220 tree/h, with men height of 30 m nd men dimeter t rest height of 41 m. The men ge of the stnds ws 120 yers. The generl spet of the site ws NE with men slope of 30%. The lef re index (LAI) ws 6.42 m 2 m -2. The historil meteorologil dt olleted in the re found tht temperture deresed y out 0.65 C for every 100 m nd nnul preipittion inresed y out 100 mm for every 100 m (Lopez Aris M, personl ommunition). A summry of the site hrteristis is given in Tle 1. Air temperture nd preipittion during the experimentl period were otined from the wether sttion in Puerto de Nverrd (1,860 m sl; Fig. 1). Soil respirtion, temperture nd moisture mesurements Mesurements of SR, ST nd SM were onduted etween spring 2005 nd summer 2006 rndomly in eh forest plot on monthly sis, using losed dynmi system LI-6400 oupled to n LI soil hmer (LI-COR in., Linoln, NE, USA). Mesurements were mde etween 10:00.m. nd 16:00 p.m. to minimize the diurnl vrition in soil respirtion using PVC ollrs (10 m dimeter nd 4.5 m length), whih were inserted into the soil t 2.5 m depth (to void root severing), t lest 1 week prior to investigtion, nd left in ple throughout the ourse of the experiment. The mesurement of SR onsisted of pling the hmer on the ollr, sruing the CO2 to su-mient levels nd mesuring the flux rte s it rose from 15 ppm elow to 15 ppm ove the tmospheri vlue. Soil respirtion smpling ws not performed on dys following rin event to void n overestimtion of the efflux due to CO2 displement from soil pores (Rey et l. 2002). A totl of 12 ollrs were pled in plots 14, 22 nd 42; wheres 9 ollrs were employed in plot 33 nd 6 in plot 100. Soil moisture ontent nd soil temperture in the top 10 m of soil were mesured next to eh soil respirtion mesurements with time-domin refletometry system (TRIMEGM, IMKO GmH, Ettlingen, Germny) nd thermoouple sensor (Omeg Engineering, Stmford, CT). Soil wter ontent ws mesured t three points round eh ollr. Soil properties Soil smpling In Mrh 2006, soil smples were tken from three different sites in eh plot. Five soil ores were extrted (10 m deep x 8 m dimeter) eneth the orgni lyer nd omposited. Soils were kept seprtely in plsti gs nd rpidly trnsported on ie in drk ooler to the lortory nd stored in refrigertor (4 C) prior to the smpling proess. Composite minerl smples were seprted into two susmples for the determintion of physio-hemil nd

3 Tle 1 Summry of site hrteristis of six study plots spred long n ltitudinl grdient in Pinus sylvestris L. forest in the northern Sierr de Gudrrm mountins Plot 14 Plot 22 Plot 33 Plot 42 Plot 100 Ltitude (N, deg.) 40 50'58" 40 50'39" 40 50'59" 40 51'15" 40 49'15" Longitude (W, deg.) 4 02'52" 4 02'52" 4 02'52" 4 02'34" 4 04'2" Elevtion (msl) 1,592 1,579 1,380 1,320 1,700 Slope (%) Aspet (deg) NNE ESE NE ESE 49 - Totl porosity (%) Prtile density (g/m ) WFP (%) ph (1:2) EC (iis/m) e e C STOCKS (kg C-irT 2 ) 5.57 ± ± ± ± ± 0.30 N STOCKS (kg N-irT 2 ) 0.30 ± ± ± ± ± 0.02 e C/N 18.7 ± ± ± ± ± 0.2 TOC (g/kg) 56.8 ± ± ± ± ± 3.6 C-TMB (g/kg) 1.30 ± ± ± ± ± e d d Mens with different letters within the site re signifintly different, using Tukey's HSD t the 0.05 level Fig. 1 Preipittion nd men temperture reorded during the experimentl period. Dt were otined from the wether sttion in Puerto de Nverrd loted pproximtely 2 km from the site of the study Preipittion - Temperture o

4 iologil soil properties. The susmple for iologil properties ws sieved through 2 mm mesh nd stored t 4 C until they were proessed. The remining smple ws ir dried t room temperture for 2-3 dys nd sieved through 2 mm sieve to remove stones, grvel nd orse deris. Soil pssing the 2 mm sieve ws grounded nd homogenized using mortr nd stored in n irtight ottle prior to determining the physio-hemil properties. Anlysis of soils Soil ph nd eletril ondutivity (EC) were mesured in 1:2 queous extrt. The ph ws mesured y mens of n ORION 720A ph-meter. Eletril ondutivity mesurements were performed y mens of n ORION 115 ondutimeter. The totl C nd N nlyses were rried out y using LECO TruSpe nlyser. The orgni ron ws nlysed with TOC-V CSH nlyser (SHIMADZU, Shimdzu Sientifi Instruments, Kyoto, Jpn). Soil moisture ontent (SM) nd dry density vlues were determined on seprte nd unltered ore smples tken t 50 mm depth using stndrd ore steel smplers (28.5 mm internl dimeter nd 34.3 mm height). Soil ulk dry density ws lulted from the dimensions of the smplers, tking into ount the oven-dried weight s the known volume of soil. The soil moisture ontent or grvimetri wter ontent ws defined s the rtio of the weight of wter nd the weight of dry soil expressed s perentge. The weight of wter ws determined s the differene etween the weight of the smple nd its weight fter oven drying t 110 C for 24 h (UNE Stndrd ). Wter filling porosity (WFP) ws lulted s: WFP (w.. x y s )/(l (Pd/y s )X where, w.. is the grvimetri wter ontent, y s is the soil prtile density nd p d is the ulk dry density. The prtile density or grin density ws mesured on powdered oven-dried speimen using the pynometer's method with wter (UNE Stndrd ). Soil miroil iomss ron ws determined y mirowve irrdition extrtion method (Islm nd Weil 1998). The orgni ron in the extrts of the ontrol nd mirowved soil were nlysed with TOC-V CSH nlyser (SHIMADZU, Shimdzu Sientifi Instruments, Kyoto, Jpn). The totl miroil iomss (C T MB) ws lulted s: CTMB = CEXTMW/0.213 where CEXTMW is the net flush of C, otined from the differene etween the extrted C in mirowved soil smples minus the extrted C in ontrol soil smples, nd is onstnt to ompenste the frtion of extrted ron y 0.5 M K 2 SQ 4. Clultion of soil ron nd nitrogen stoks Cron nd N pools (or stoks) in the top 10 m of minerl soil (kg m~ ) were estimted y multiplying vlues of perent C nd N in the minerl soil y soil-ulk density mesurements from eh plot. Sttistil nlysis nd modelling Plot-level sesonl temperture response of SR ws lulted y mens of gio funtion s mentioned y Jnssens nd Pilegrd (2003), whih is lled temperture sensitivity of SR: sr = ^oxer io)/10) ; (i) where SR (umol C02-m~ s~ ) is the soil respirtion flux, R w is the simulted SR t soil temperture of 10 C, whih is often used to ompre the SR hrteristis of eosystems, <2io is the temperture sensitivity of SR (the respirtory flux t one temperture over the flux t temperture 10 C lower), nd Tis the mesured soil temperture ( C). The funtions were fitted to the mesured dt y mens of nonliner lest squre fitter (Sigm Plot 6.0). All sttistil nlyses were performed using the Sttisti 6.0 softwre pkge (SttSoft. In., Tuls. USA). Site (plot) nd time effets for soil respirtion, soil temperture nd soil moisture were tested with repeted mesures nlysis of vrine (ANOVA). One-wy nlysis of vrine ws used to test for the effets of stnd on soil respirtion in the sites where there ws no omplete set of dt ville nd to nlyse the differenes in soil properties etween plots. The norml distriution nd homogeneous vrine were tested y the Kolmogorov- Smirnov nd Levene's tests, respetively. Post ho omprisons were tested using Tukey's HSD test, lulted t the 5% level. Whenever neessry, dt were trnsformed s (x + l) 0,5 or log x. Correltion nlyses from the dt of the entire dt set were used to exmine the reltionship etween soil respirtion rtes nd soil properties. Results Soil respirtion Soil respirtion vlues during the experimentl period (June 2005-July 2006; Fig. 2) vried from 6.8 ± 0.2 umol m~ s~ in June 2005 to 1.4 ± 0.1 umol m~ s~ in Ferury Soil respirtion ross the six study sites showed typil sesonl pttern with mximums in spring nd summer nd minimums in winter. Sesonl ptterns

5 Soil temperture nd moisture CM 3 O 4 E zi. tn o OT j O * h- U) A » JN 05 JL 05 FB 06 MC 06 MY 06 JN 06 JL 06 Fig. 2 Sesonl vritions of oserved soil respirtion (SR, umol m~ 2 s _1 ), volumetri wter ontent (SM, %), soil temperture t 10 m soil depth (ST, C) for study plots in Vlsin during the period Asterisk indites signifint differenes t the 0.05 level were similr in the different plots, lthough temporl flututions were more limited in plots 42 nd 100. Repeted mesures nlysis of vrine indited tht SR ws different mong sites (F 3;131 = 31, 871; P = 0.0) nd time of the yer (^5, , 29; P = 0.0). Men vlues in plot 22 were intermedite (P < 0.05) etween the highest vlues of plots 14 nd 33 nd the lowest vlues of plot 42 during July 2005, June 2006 nd July Plot 100 showed low vlues (P < 0.05), similr to those found in plot 42, nd signifintly different from the rest of the plots. 33 Both soil temperture nd moisture ontent vried ording to the seson. Mximum soil temperture oinided with minimum soil moisture during the summer, nd minimum soil tempertures were reorded in winter when soil moisture ws highest (Fig. 2). Soil temperture vried with site (P = 0.0), time (P = 0.0) nd site over time (P = 0.0). There ws signifint site effet (P < 0.05), with plot 42 exhiiting the highest soil temperture followed y plot 22, 33 nd finlly 14. Soil temperture ws highest in July 2006, delined in June 2005, followed y My 2006 nd Mrh 2006, nd dropped to minimum in Ferury Plot 100 showed the highest vlues during My 2006 nd June Soil moisture differed over time (P = 0.0), site (P = 0.0) nd site over time (P = 0.0). Soil moisture ws highest (P < 0.05) in plots 14 nd 33 nd lowest in plots 22 nd 42. Soil moisture during My 2006 ws higher (P < 0.05) in plot 14, while no signifint differene ws oserved mong the other plots. During June 2006, soil moisture ws higher in plot 14 thn in plot 42. For ll tretments, soil moisture rose to mximun in winter nd spring months nd delined stedily through June to minimum in July. Influene of temperture nd moisture on soil respirtion Not surprisingly, oth soil temperture nd moisture were highly signifint in regression nlysis explining lrge perentge of the sesonl vriility in soil respirtion. Soil moisture showed signifint negtive orreltions to sesonl soil respirtion for plot 14 (r = 0.28, r = 0.53, P = 0.0), plot 22 (r 2 = 0.39, r = -0.63, P = 0.0), plot 33 (r 2 = 0.36, r = -0.60, P = 0.0) nd plot 42 (r 2 = 0.06, r = 0.25, P = 0.0); while positive orreltions were ssoited with plot 100 (r 2 = 0.10, r = 0.32, P = 0.0). Soil respirtion ws stisftorily represented s funtion of temperture, using the <2io-type model fitted to the entire dt set (Fig. 3). In plot 100, soil respirtion nd soil temperture were not orrelted. The temperture-sed gio models hd similr gio vlues rnging etween 1.30 nd The R w vlues rnged etween 2.0 nd In plots 33 nd 42, n intertion etween soil temperture nd soil moisture explined 40 nd 36% of the vriility, respetively (Tle 2). Influene of soil prmeters on soil respirtion Soil ron stoks vried etween 5.57 ± 0.2 kg m~ (plot 14) nd 7.76 ± 0.2 kg m -2 (plot 22), while soil nitrogen ontent vried from 0.27 ± 0.01 kg m -2 (plot 42) to 0.42 ± 0.02 kg m" 2 (in plot 100; Tle 1). Regrding

6 Fig. 3 Soil C0 2 efflux versus soil temperture s mesured in Spnish Sots pine forest. The solid line represents the est fitting Qio funtion. Funtions were fitted through the entire dt set. R 2 represents the proportion of vriility in soil respirtion explined y soil temperture SRVSSTPLOT14 SRVSSTPLOT Soil temperture ( C) SRVSSTPLOT Soil temperture ( C) SRVSSTPLOT Q10 funtion; R10=3.45; Q10=1.68 R 2 =0.35 p< o - Q10 funtion; R10=2; Q10=1.30 R 2 =0.22;p< ' 6 Q I! *is 8 3 ^ 0 Q **T ^ o n Soil temperture ( C) Soil temperture ( C) Tle 2 Soil respirtion s funtion of temperture nd moisture ontent, using fitted liner urve through the entire dt set Model r 2 P Plot 33 SR = x ST x SM Plot 42 SR = x ST x SM miroil iomss ron (C-TMB), plot 14 showed the highest ontent, while the urned plot (plot 100) hd the lowest. Soil respirtion (Tle 3) ws positively orrelted with C nd N stoks nd WFP, nd negtively orrelted to totl porosity. Although not signifintly, soil respirtion tends to inrese with C-TMB, TOC, ph nd C/N. Disussion nd onlusions The vlues of soil respirtion in this re re in rnge omprle with those mesured in other Mediterrnen forests (Rey et l. 2002; Rodeghiero nd Cestti 2005; Tedeshi et l. 2006). The nnul <2io derived from the dt set were lower thn the glol medin of 2.4 (Rih nd Shlesinger 1992) nd the rnge dt ( ) reported for forest eosystems (Jnssens et l. 2003). Our estimtes of Rio ( ) re in greement with the rnge ( umol m~ s~ ) oserved in Europen forests (Jnssens et l. 2003). We found similr Q 10 nd R w vlues s were oserved y Tng et l nd Rodeghiero nd Cestti 2005 in Mediterrnen eosystems. The resons for redued temperture sensitivity in Vlsin forest re unler, nd depend on the environmentl onstrints (generlly low soil moisture ontent) nd the sustrte. The results indite tht SR sesonl vrition ws minly dominted y ST (Fig. 3) nd tht soil moisture lso hd n importnt influene on SR. However, the influene of SM on SR depends on the site. In plot 100, the temporl vrition in SR ws minly ontrolled y soil moisture, nd in plots 33 nd 42 the intertion etween ST nd SM explined most of the vriility oserved. Although it is diffiult to seprte ompletely the influene of ST nd SM imposed on SR, our short-term oservtion showed tht SR responded minly to ST in winter nd tht the intertion of soil temperture nd moisture on SR ws espeilly pprent during the summer months when low soil moisture limited soil miroil tivity nd root growth despite wrm soil temperture (Fig. 2). In the Vlsin mountins, in situ mesurements of soil respirtion deline with delining ltitude in ontrst with other field studies tht indite orreltions etween SR nd elevtion (Wng et l. 2000; Rodeghiero nd Cestti 2005; Grten nd Hnson 2006). Wheres the wrmest tempertures were ssoited with the lowest elevtion site (plot 42), the highest rtes of SR were oserved t the highest elevtion plots (14, 22 nd 33). The elevtion ftor lone my not explin the SR sensitivity y itself. Topogrphy produes sptilly heterogeneous SM nd thus soil respirtion. In our study, more mesi north-fing slopes (plot 14 nd 33) showed higher SR reltive to less

7 Tle 3 Correltion oeffiients etween vrious soil vriles nd soil respirtion (SR, umol m s ) t Mrh 2006 in Pinus sylvestris L. forest in the Sierr de Gudrrm C.stoks N.stoks C/N C-TMB TOC Prtile density Totl porosity WFP ph EC (kg-c-m- 2 ) (kg-nirt 2 ) (g-kg- 1 ) (g-kg- 1 ) (g-m- 3 ) (%) (%) (1:2) (ns-irr 1 ) SR Q w R Bold numers indite signifint orreltion t P < 0.05 mesi south-fing slopes (plot 22 nd 42) despite higher ST t south-fing slopes. The role of temperture nd soil moisture in SR under field onditions is not lwys strightforwrd nd my e influened y vegettion overs, litter hemistry nd thikness, soil orgni mtter, vrile rtes of elowground root growth nd tivity, N vilility nd soil hrteristis. All these ftors potentilly intert in omplex wys through effets on deomposition. In our experiment, we otined SR, Qw nd RJO vlues higher in the ooler, wetter site reltive to the wrmer, drier site. This is in greement with Xu nd Qi (2001). If we ompre this trend with C-TMB (derese in the sme wy), we ould explin this ehviour y fster response of the miroil ommunity to wrming when esily degrdle sustrte ility is lso high. In our experiment, the positive orreltions etween SR, Qw nd R 10 vlues nd C nd N stoks, TOC, C-TMB nd WFP (Tle 3) indited tht miroil sustrte quntity nd nitrogen-rih onditions promote higher Qw nd SR vlues. Atmospheri deposition nd litter fll inputs ould influene SR long the ltitudinl trnset. Prior studies long the elevtion grdient in Vlsin indited deline in litter fll inputs nd N deposition with deresing ltitude (Gonzlez Cson et l. 1994; Gri del Brrio et l. 1997). At low elevtions, oth higher men nnul tempertures nd lower site N vilility potentilly ontriute to lower soil C stoks nd shorter turnover time for lile soil C. The highest vlues of SR in plot 14 lso ould e relted to higher pine density nd regenertion in this plot, nd to differenes in root respirtion. Results from studies of other forests indite tht fine root iomss is diretly ssoited with tree sl re (Chen et l. 2004). Our results revel tht fire n lter the level of C, N, ph, nd C-TMB in the soil. The inreses in C onentrtion during the first yers fter the fire ould e ttriuted to unurnt remins from ded roots, whih slowly inorporte into the soil. C/N rtios were lower in the urnt soils thn in the unurnt soils. Altertion of nitrogen y fire is omplex proess. Fire lters the mount of nitrogen in the soil y voltiliztion of some into the tmosphere nd y onverting the nitrogen into different nitrogen ompounds. The ph deresed fter the fire. The urnt plot exhiited redued miroil iomss C ompred to mture plots. This dt reveled tht fire ltered the miroil diversity of the soil eosystem. After the fire, C-TMB ws very low, whih indites tht miroil diversity hd deresed signifintly even 2 yers fter the ourrene of the disturne. Dereses in miroil iomss hve een widely reported fter fire. In the urnt plot, SR, Q 10 nd R 10 were lower thn in unurnt plots. From the results otined, it n e onluded tht under similr limti onditions nd soil types within smll geogrphil re, vrition in soil temperture, soil moisture, ron nd nitrogen stoks nd C-TMB n influene SR in southern Pinus sylvestris L. forest. Thus hnges in soil prmeters over smll sles need to e onsidered when modelling lndspe-level SR. Furthermore, etter understnding of how nturl disturnes ffet C nd N yling is ruil for prediting how hnges in limte nd disturne regimens will ffet the exhnge of C etween forest eosystems nd the tmosphere. Aknowledgments This reserh ws onduted in the frmework of Spnish HU , AGL nd CGL / CLI projets nd the Europen COST 639 (BurnOut) projet. The uthors would like to express their grtitude to Mr. Jvier Dones, Mr. Mnuel Lopez Aris nd Mr. Jose M. Gru for their vlule ssistne with field spets nd for the dt provided. Referenes Chen W, Zhng Q, Chilr J, Buhus J, Prie DT (2004) Estimting fine-root iomss nd prodution of orel nd ool temperte forests using ove-ground mesurements: new pproh. Plnt Soil 256:31^6. doi: /slll Cox PM, Betts RA, Jones CD, Spll SA, Totterdell IJ (2000) Aelertion of glol wrming due to ron yle feedks in oupled limte model. Nture 408(6809): doi: / Dvidson EA, Belk E, Boone RD (1998) Soil wter ontent nd temperture s independent or onfounded ftors ontrolling soil respirtion in temperte mixed hrdwood forest. Glo Chng Biol 4: doi: /j.l x Dilustro JJ, Collins B, Dunn L, Crwford C (2005) Moisture nd soil texture effets on soil CQ 2 efflux omponents in

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