Impacts of climate change on microbial diversity in Arctic permafrost and considerations for modeling this system in transition

Robyn A. Barbato, Army, US Army Cold Regions Research and Engineering Lab, Hanover, NH, Stacey Doherty, Robert Jones and Alison Thurston, Army, US Army Cold Regions Research and Engineering Laboratory, Hanover, NH, Thomas Douglas, Army, Cold Regions Research and Engineering Laboratory, Fort Wainwright, AK

Background/Question/Methods:
Permafrost is thawing at unprecedented rates, significantly altering the landscape through changing subsurface conditions, soil properties, and vegetation characteristics. Permafrost microbes activate as permafrost soils warm and thaw. The contribution of temperature or starting inoculum on the microbial trajectory and potential function after thaw remains a research gap. We hypothesize that the initial soil microbial composition rather than the temperature dictates the end-state microbial community. We sampled permafrost from five discrete locations representing different ages of deposition in the Cold Regions Research and Engineering Laboratory Permafrost Tunnel in Alaska. In a laboratory incubation study, we gradually warmed the permafrost samples from -3˚C to 6˚C and continuously measured heterotrophic respiration. DNA was extracted and metagenomes were analyzed.
Results/Conclusions:
Under frozen conditions, microbial respiration rates from different PT locations were similar to one another, ranging from 2 to 12 mg C-CO2 kg-1 d-1. Respiration increased during thaw for three of the permafrost locations, but remained stable for two of the permafrost locations. There was an average of 21.9 million reads per sample. Analysis of the shotgun metagenomes revealed that the trajectory of dominant taxa and their potential function during thaw in a given permafrost location was more influenced by starting inoculum than by incubation temperature. Location was found to be a significant (p = 0.001) factor in differentiating taxonomy and potential functional profiles. Furthermore, the five most abundant classes in the permafrost samples include Alphaproteobacteria, Actinobacteria, Clostridia, Betaproteobacteria, and Bacilli. The differential response of microbiome from different locations has important implications for modeling soil biochemical processes across a dynamic landscape. What remains unknown are the effects of long-term thaw and in turn microbial composition on soil function.