Linking organic matter breakdown to abundance and community composition of denitrification and DNRA microorganisms in tidal wetlands

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1 Linking organic matter breakdown to abundance and community composition of denitrification and DNRA microorganisms in tidal wetlands Ember Morrissey, Jaimie Gillespie, Joseph Morina, and Rima Franklin Virginia Commonwealth University, Department of Biology, Richmond, VA

2 Anthropogenic Nitrogen

3 Nitrogen Cycling in Freshwater Wetlands Incorporated into plant biomass N 2 & N 2 O NO - DNRA 3 NH + 4 N exported to ecosystems downstream Burial in the sediment Microbial activity, fueled by high SOM from plant production

4 Nitrogen Cycling in Freshwater Wetlands Incorporated into plant biomass N 2 & N 2 O What environmental variables regulate the abundance of DNF and DNRA microbes? What controls community composition within each functional group? NO - DNRA 3 NH + 4 N exported to ecosystems downstream Burial in the sediment Microbial activity, fueled by high SOM from plant production

5 Experimental Design Mattoponi June 2010 Pamunkey Sampled 9 tidal freshwater wetlands in Virginia Chickahominy Selected for dominance of Peltandra virginica (> 50%) James River 0.25 m 2 ph Redox % Moisture Plants (above ground biomass) Roots (below ground biomass) 10 m

6 Functional Gene Assays for DNF & DNRA (1) Abundance of each group: quantitative PCR (qpcr) to determine the abundance of selected functional genes (2) Composition: Terminal Restriction Fragment Length Polymorphism (T-RFLP) Fingerprinting technique to evaluate the presence and absence of different microbes Separate profiles for DNF- and DNRA-capable organisms The Evolution and Future of Earth s Nitrogen Cycle Canfield et al. Science (2010)

7 Characterizing Sediment Organic Matter (1) Amount available as %OM (2) C:N as traditional quality metric High C:N recalcitrant OM Low C:N labile OM (3) Extracellular enzyme activity: Proxy for OM quality Microbes produce enzymes targeted to local substrate conditions Enzymes for labile carbon substrates Cellulose -1,4-glucosidase (BG) Cellulose 1,4- cellubiosidase (CB) Enzymes for recalcitrant substrates Lignins Phenol Oxidase (PO) Hemicellulose -D-xylosidase (Xylo) cellobiosidase + 4-Methylumbelliferyl β-d-cellobioside (proxy for cellulose) β-d-cellobiose Methylumbelliferone + fluorescence

8 Principal Component 2 (29%) Site Differences- Biotic Environments Principal Components Analysis of Organic Environment Mattoponi Pamunkey Chickahominy James River Principal Component 1 (36%)

9 Site Differences - DNF & DNRA abundance Mattoponi Pamunkey Chickahominy James River No consistent trend within or between rivers Generally DNF organisms are much more abundant than DNRA Do these patterns correlate with our environmental data?

10 Regression Analysis Predictors of Functional Group Abundance Mixed direction stepwise (inclusion α=0.05) Response - DNF or DNRA abundance (g -1 dry sediment) Predictors ph, redox, plant biomass, %OM, C:N, enzyme activity

11 Regression Analysis Predictors of Functional Group Abundance Mixed direction stepwise (inclusion α=0.05) Response - DNF or DNRA abundance (g -1 dry sediment) Predictors ph, redox, plant biomass, %OM, C:N, enzyme activity Predictors: Adj R 2 (p-value) DNRA C:N (+) 0.28 (<0.001) Roots (-) %OM (-)

12 Regression Analysis Predictors of Functional Group Abundance Mixed direction stepwise (inclusion α=0.05) Response - DNF or DNRA abundance (g -1 dry sediment) Predictors ph, redox, plant biomass, %OM, C:N, enzyme activity Predictors: Adj R 2 (p-value) DNRA C:N (+) 0.28 (<0.001) Roots (-) %OM (-) DNF C:N (-) 0.29 (<0.001) Plants (+) ph (+)

13 Do the same things that regulate abundance also regulate community composition?

14 Do the same things that regulate abundance also regulate community composition? Well. Yes and No!

15 Axis 2 (30%) Axis 2 (30%) Drivers of Community Composition DNRA DNF Axis 1 (31%) Axis 1 (32%) Mattoponi Pamunkey Chickahominy James River

16 So what do these relationships mean for biogeochemical activity? Roots Recalcitrant EEA % Organic Matter Redox Labile EEA C:N Ratio Plants

17 So what do these relationships mean for biogeochemical activity? Roots Recalcitrant EEA % Organic Matter Redox Labile EEA C:N Ratio Plants DNRA Community Composition

18 So what do these relationships mean for biogeochemical activity? Roots Recalcitrant EEA % Organic Matter Redox Labile EEA C:N Ratio DNRA Community Composition Plants DNF Community Composition

19 So what do these relationships mean for biogeochemical activity? DNRA Community Composition DNRA Community Activity Roots Recalcitrant EEA % Organic Matter Redox Labile EEA C:N Ratio Plants DNF Community Composition DNF Community Activity

20 So what do these relationships mean for biogeochemical activity? DNRA Community Composition DNRA Community Activity Roots Recalcitrant EEA % Organic Matter Redox Labile EEA C:N Ratio Plants DNF Community Composition DNF Community Activity Ecosystem NO 3 - Reduction

21 So what do these relationships mean for biogeochemical activity? N 2 & N 2 O NO - 3 DNRA NH + 4 N exported to ecosystems downstream

22 So what do these relationships mean for biogeochemical activity? N 2 & N 2 O DNRA NO 3 - NH 4 + N exported to ecosystems downstream

23 So what do these relationships mean for biogeochemical activity? N 2 & N 2 O NO - 3 DNRA NH + 4 N exported to ecosystems downstream

24 Acknowledgements Thanks to everyone in the Franklin Lab! Special thanks to the 9th INTECOL International Wetlands Conference organizers for volunteer support. Funding SWS South Atlantic Chapter Travel Award SWS Student Research Award Rice Center Student Research Award VCU HHMI Summer Scholars Program Jaimie and Joey

25 Site Differences - DNF & DNRA abundance Mattoponi Pamunkey Chickahominy James River No consistent trend within or between rivers Generally DNF organisms are much more abundant than DNRA Do these patterns correlate with our environmental data?

26 Regression Analysis Predictors of Functional Group Abundance Mixed direction stepwise (inclusion α=0.05) Response - DNF or DNRA abundance (g -1 wet sediment) Predictors ph, redox, plant biomass, C:N, % OM, enzyme activity Predictors: Adj R 2 (p-value) DNRA C:N (+) 0.33 (<0.001) % OM (-) Roots (-) DNF C:N (-) 0.45 (<0.001) % OM (-) Plants (+) ph (+)