Freshwater wetlands play a critical role in the global C cycle as they are highly productive ecosystems with net primary productivity comparable to agricultural lands [1]. Much of this fixed C is allocated belowground where it accumulates as soil organic matter (SOM). Despite this high primary productivity, wetlands can be net sources of CH4 and N2O to the atmosphere, potentially offsetting the climate benefits of carbon sequestration through slow decomposition. Changing global precipitation regimes are thought to affect the frequency and duration of flooding in freshwater wetlands, collectively shifting soil oxidation-reduction (redox) potential. Wetlands with prolonged, deep flooding have very low redox potentials that lead to accumulation of humics (which can act as electron donors and terminal electron acceptors) and the production of CH4; meanwhile N2O production is favored in wetlands where the duration of flooding is brief. Shifts in the availability of terminal electron acceptors (TEAs) such as iron, sulfur and nitrate can influence the relative abundance of anaerobic respiratory microorganisms, which can alter the time-to-onset of methanogenesis following an oxidation event as well as the flux of methane due to competition between methanogenic archaea and anaerobic respiratory bacteria for electron donors (e.g. hydrogen and acetate). Additionally, TEAs such as iron, sulfate, and nitrate can be coupled to anaerobic methanotrophy, further modulating net methane flux. We are applying 16S amplicon sequencing, and metagenomic-enabled genome reconstruction to explore the microbial ecology of methane-metabolism in these complex systems. The data presented here are from both field and microcosm studies.
Results/Conclusions
We utilized extensive 16S rRNA amplicon sequencing data to correlate floodplain sites at different ages since restoration (<5 years, 5-10 years, >10 years) to the microbial ecology particular to that site. Additionally, moisture, depth, terminal electron acceptor concentrations, pH, and methane flux are all examined to ascertain the complexities of microbial activity in response to land-use change. Results from this study indicate that the variability of the microbial communities could largely be explained by site location, soil depth, C:N ratio, and pH. Microbial diversity was higher at older floodplains and decreased with deeper sampling depths. Additionally, the Deltaproteobacteria were significantly enriched at lower depths compared to Verrucomicrobia and Bacteroidetes. Furthermore, each site had specific microbial signatures. We propose that these signatures could eventually be used for determining floodplain health and predictive modeling of greenhouse gas emissions from waterlogged soils.