Vertical distribution patterns and potential activities of methanogenic and methanotrophic communities in permafrost peatlands of Greater Khingan Mountains

• The diversity of methanogens and methanotrophs was higher in the transitional layer. • The relative abundance of methylotrophic methanogens and type II methanotrophs increased along the peatland-forest ecotone. • Methanotroph communities gradually lost complexity and stability from tussock peatland to forested peatland. • The vegetation type and soil depth jointly affected the community structure of methane-cycling microorganisms. • Soil environmental factors impacted mcrA and pmoA gene abundance as well as potential methane production and oxidation rates. Peatlands are dominant sources of methane (CH 4 ), and warming-induced permafrost degradation alters vegetation composition and water table, which dramatically reshape the microbial-mediated CH 4 cycling processes, possibly resulting in strong positive feedbacks of carbon loss and climate change. It is essential to understand the biological mechanisms of CH 4 emission by peatlands for future climate projections. Here, we examined the vertical distribution patterns of methanogen and methanotroph community composition, abundance, and activities in three different peatlands along the peatland-forest ecotone transect of the Greater Khingan Mountains permafrost region in Northern China. The alpha diversity of methanogens and methanotrophs was higher in the transitional layer compared to the deep anoxic and upper oxic layers. Hydrogenotrophic methanogens were absolutely dominant in tussock peatland (TP), whereas methylotrophic methanogens increased in forested peatland (FP) and shrubby peatland (SP). Type II methanotrophs were dominant in FP and SP, while type I methanotrophs dominated in TP. Co-occurrence network analysis revealed that environmental filtering had a slight effect on methanogen communities, but the complexity and stability of methanotroph communities decreased from TP to FP. Potential methane production rates (MPR) and methane oxidation rates (MOR) reached a maximum in the deep anoxic and transitional layers, respectively, and mcrA gene abundance increased along the soil profiles, whereas pmoA displayed the opposite trend. Partial least squares path modeling (PLS-PM) analysis showed that abundance of mcrA and pmoA , as well as MOR, were all associated with soil water content (SWC) and dissolved organic carbon (DOC), while MPR was correlated with inorganic nitrogen content. These results provide unique insights into forecasting the response of microbial functional groups driving CH 4 cycling in peatlands to climate change in high-latitude permafrost regions.