Abrupt permafrost thaw triggers microbial bloom and increased activity of microbial predators

Abstract

AbstractPermafrost soils store a substantial part of the global soil carbon, but due to global warming, abrupt erosion and consecutive thaw make these carbon stocks vulnerable to microbial decomposition into greenhouse gases. Although in temperate systems trophic interactions promote soil carbon storage, their role in Arctic permafrost microbiomes, especially during thaw, remains largely unknown. Here, we investigated the microbial response to in situ thawing and rapid permafrost erosion. We sequenced the total RNA of a 1 m deep soil core from an active abrupt erosion site to analyse the microbial community in the active layer soil, recently thawed and intact permafrost, consisting of up to 26 500-year-old material. We found maximum RNA:DNA ratios in recently thawed permafrost, indicating upregulation of protein biosynthesis upon thaw. At the same depths, the relative abundance of several prokaryotic orders, including Sphingobacteriales, Burkholderiales, and Nitrosomonadales increased in relative abundance. Bacterial predators were mainly dominated by Myxococcales. Protozoa were overall less abundant but doubled in relative abundance between the active layer and recently thawed permafrost. Cercozoa, Amoebozoa, and Ciliophora were the most abundant protozoan predators, replacing myxobacteria at deeper thaw depths. Overall, connections between the active layer and especially upper thawed layers were visible and suggest migration, while no layer formed a distinct community. Our findings highlight the importance of predation and population dynamics as well as the rapid development of a microbial bloom in abruptly thawing permafrost.