| Summary: | A large portion of the World’s terrestrial organic carbon is stored in Arctic permafrost soils.However, due to permafrost warming and increased in situ microbial mineralisation of released carbon,greenhouse gas releases from Arctic soils are increasing, including methane (CH4 (g) ). To identify environ-mental controls on such releases, we characterised soil geochemistry and microbial community conditions in13 near-surface Arctic soils collected across Kongsfjorden, Svalbard. Statistically significant correlationswere found between proxies for carbonate mineral content (i.e. Ca and Mg) and soil pH (Spearman rho =0.87, p \ 0.001). In turn, pH significantly inversely correlated with bacterial and Type I methanotrophgene abundances across the soils (r =-0.71, p = 0.01 and r =-0.74, p = 0.006, respectively),which also co-varied with soil phosphorous (P) level (r = 0.79, p = 0.01 and r = 0.63, p = 0.02, respec-tively). These results suggest that soil P supply, which is controlled by pH and other factors, significantlyinfluences in situ microbial abundances in these Arctic soils. Overall, we conclude microbial responses toincreasing ‘old carbon’ releases in this Arctic region are constrained by nutrient-deficiency in surface soils,with consequential impacts on the flux and composition of carbon gasses released to the atmosphere.
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