PS 47-207 - Microbial dynamics dictate carbon dioxide flux from permafrost thaw

Abstract: Arctic systems are experiencing warming at more than three times the rate of the global average, leading to permafrost thaw and exposing previously protected soil carbon and nutrients to microbial decomposition. When soils thaw, microbes can decompose this carbon, resulting in the release of greenhouse gases into the atmosphere. This contributes to the permafrost carbon-climate feedback and can increase warming in the Arctic. Permafrost soils contain a diverse array of active, dead, and dormant microbial communities that experience biological, environmental, and ecological change during thaw. The objectives of this study were to quantify permafrost bacterial abundance in permafrost soils before and after thaw, identify bacterial taxa that respond positively by increasing in abundance post-thaw, and understand the microbial contribution to carbon dioxide flux. We thawed permafrost from three Alaskan sites for 3-months, during which we monitored carbon dioxide fluxes, followed by 16S rRNA gene amplicon sequencing and quantification of the bacterial biomass with qPCR. We found carbon dioxide respiration was positively correlated with the size of the post-thaw bacterial biomass pool (Spearman’s rank correlation rho = 0.618, p-value < 0.05), but not pre-thaw biomass, suggesting that an increase in microbial carbon dioxide production post-thaw is due to an increase in microbial activity, such as the formation of new biomass. Microbial thaw response was assessed in taxa across sites. Members from phyla Actinobacteria, Firmicutes, and Bacteroidetes increased in abundance due to thaw which was observed across all three sites. An increase in these phyla post-thaw proves to be consistent with previous permafrost studies from other sites in Alaska, Siberia, and Norway. The results of this study demonstrate that permafrost thaw accelerates microbial activity, alters community dynamics, and causes a positive response from select taxa, all of which influence the trajectory of Arctic ecosystem structure and function in a changing climate.