Methane-cycling microbiomes in soils of the pan-Arctic and their response to permafrost degradation.

The methane-cycling microbiomes play crucial roles in methane dynamics. However, little is known about their distributions on a pan-Arctic scale as well as their responses to the widespread permafrost degradation. Based on 621 datasets of 16S rRNA gene amplicons from intact permafrost soils across the pan-Arctic, we identified only 22 methanogen and 26 methanotroph phylotypes. Their relative abundances varied significantly between sites and soil horizons. Only four methanogen phylotypes were detected at all locations. Remarkably, the permafrost soil methane filter was almost exclusively dominated by some obligate methanotroph (Methylobacter-like) phylotypes. However, a case study in Alaska suggests that atmospheric methane oxidizing bacteria (Methylocapsa-like phylotypes) dominated methanotrophs in a drier condition after permafrost degradation. These findings point towards a few key microbes particularly relevant for future studies on Arctic methane dynamics in a warming climate and that under future dry conditions, increased atmospheric methane uptake in Arctic upland soils may occur.