B022-0017
Microbe-substrate interactions following simulated microbial inoculation to thawed yedoma permafrost

Tuesday, 8 December 2020
Poster
Joanne K. Heslop1, Matthias Winkel1, Katey M Walter Anthony2, Rob Spencer3, David C Podgorski4, Phoebe Zito4, Rebecca Bergquist Neumann5 and Susanne Liebner6, (1)Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany, (2)University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK, United States, (3)Department of Earth, Ocean and Atmospheric Sciences, Florida State University, Tallahassee, FL, United States, (4)University of New Orleans, Department of Chemistry, New Orleans, LA, United States, (5)University of Washington, Seattle, WA, United States, (6)GFZ German Research Centre for Geosciences, Section Geomicrobiology, Potsdam, Germany
Abstract:
The relative roles of ancient versus modern microbial community activities in yedoma permafrost carbon decomposition is unknown. We use a microscale-level approach to examine: (1) interaction between thawed substrate and microbial community composition; (2) how mixing modern CH4-producing communities with microbial communities present in frozen permafrost affects community composition following thaw; and (3) subsequent effects on CO2 versus CH4production. We anaerobically incubated sediments collected from a 12-m yedoma profile in Interior Alaska using two treatments: controls (unaltered sediment) and inoculated with surface sediment from an adjacent thermokarst lake. For most depths, inoculation with modern CH4-producing communities increased CH4 (7.6 - 390x) and CO2 (1.0 - 2.7x) production and decreased CO2:CH4 ratios (36 – 99 % decrease) compared to controls. The inoculations had the strongest effects in yedoma sediments that had not thawed since their formation. Coupled with high initial substrate potentials (high relative abundance of aliphatic- and peptide-like compounds) measured in the yedoma via FT-ICR-MS, this suggests greenhouse gas (GHG) production in thawed yedoma is microbially-limited. Interestingly, at our deepest depth (12 m) inoculation decreased CH4 production by 30% and CO2 production by 60-70% compared to controls. Based on analyses of substrate utilization (FT-ICR-MS) in conjunction with microbial community characterization (16S RNA sequencing) and metabolic pathways (Bayesian geochemical rate modeling), we suggest proportions of CH4 produced via hydrogenotrophic versus acetoclastic methanogenesis affected both GHG production rates and proportions of C mineralized as CO2 versus CH4. Incorporating this microscale approach into larger models will aid in accounting for the complexities and interactions present in natural systems, and potentially work towards reconciling discrepancies in GHG emissions estimated using experimental versus modeled approaches.
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