| Summary: | Arctic permafrost is estimated to store 1850 Gt carbon (C), corresponding to about twice the amount of current atmospheric CO2. After being frozen for a minimum two but often thousands of years, microorganisms inhabiting these soils face new environmental conditions upon thawing. Gaps of knowledge exist in their metabolic response to increasing lability of ancient C stocks under warmer temperature regimes and liquid water availability. Microbial conversion of these C stocks potentially acts as sink or source of greenhouse gases, such as CO2 and CH4 and could further impact C fluxes to the atmosphere. These carbon decomposition processes have implications for predictions in global models. Hence, knowledge about microbial carbon sequestration in thawing soils is crucial - yet understudied, particularly in remote environments. Environmental total RNA reflects all genes expressed by the soil microbiome in response to physicochemical conditions, such as abrupt thaw and erosion. Taxonomic composition, community changes, possible survival mechanisms as well as metabolic pathways of microbial organic carbon remineralization, methanogenesis and/or trophy of soil microorganisms will be revealed. Here, we sampled the seasonally thawing active layer, freshly thawed transition zone and intact permafrost layer of a 2-year-old abruptly collapsed thermal erosion gully in the remote high Arctic, Zackenberg, Northeast Greenland. From a 1 m deep and up to 26200-year-old soil core, total RNA was extracted and sequenced with Illumina NextSeq. Gene expression of samples describes the community composition (rRNA) and organism-level active metabolic pathways (mRNA) in zones of intensely degrading permafrost. The impact of changing physicochemical soil parameters with depth, such as pH, age, soil moisture and organic matter content was compared to determine possible metabolic and community-level responses. Implementation of bio-indicator signatures in thawing permafrost soils for monitoring was investigated.
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