| Summary: | Permafrost preserves vast amounts of carbon in the form of ancient undecomposed or partially decomposed plant detritus. Climate change is currently thawing permafrost, making this carbon available to permafrost microbial communities, who degrade it and release globally significant amounts of greenhouse gasses. The characteristics of permafrost carbon, its susceptibility to degradation, and the structure of microbial communities that inhabit permafrost are likely strongly influenced by the vegetation present (and thus the detrital material) during permafrost formation. However, the effect of site history and paleovegetation on permafrost microbial communities has not been examined at scale. To reconstruct paleovegetation from permafrost samples ranging in age from approximately 2000 to 880,000 years old, we mined 133 permafrost metagenomes for DNA sequences originating from plant material and performed taxonomic reconstructions. Here we show that paleovegetation of steppe, tundra, and boreal forest biomes shapes the taxonomy and functional potential of soil microbes. Moreover, we show that paleovegetation affects community composition at every trophic level, from bacteria to soil protists, terrestrial arthropods, and animals, and the effect is distinct from soil physiochemical parameters. Permafrost microbial communities may subsequently have a role in shaping the vulnerability of permafrost soil to thaw and subsequent release of greenhouse gasses. Understanding these effects may be important to predicting the ultimate consequences of permafrost thaw to climate change. 2 years by Michael Snyder
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