Divergent Responses of Methane Emission to Warming in Waterlogged Versus Drained Alpine Peatlands.

Peatlands are a major natural source of atmospheric methane (CH4). Yet their responses to warming remain highly uncertain, because ecosystem-level understanding of warming effects on CH4 production and oxidation is limited. Here, we conducted an open-top chamber (OTC) warming experiment in the world's largest alpine peatlands (Zoige) under both waterlogged and drained regimes. We monitored stable carbon isotopic composition (δ13C) of CH4 and CO2 in soil gas and porewater throughout five growing seasons, coupled with net CH4 fluxes, to tease apart OTC warming effects on methanogenesis (quantified as in situ CH4 production, PCH4) and methanotrophy (quantified as the fraction of CH4 oxidized during upward diffusion, fox). Warming did not alter net CH4 fluxes from the waterlogged regime, because PCH4 and fox declined concurrently owing to enhanced iron reduction and elevated reducing conditions, respectively. In contrast, OTC warming reduced net CH4 fluxes by ~60% from the drained regime, mainly because methanotrophy intensified (mean fox increased by 41%) due to increased oxygen availability and reduced aerenchymatous plant biomass. The decline in aerenchymatous plants limited plant-mediated transport and bypass of CH4 across the oxic soil layer. Enhanced methanotrophy was further supported by increased soil abundance of methanotroph-specific phospholipid fatty acid markers. Collectively, our results reveal contrasting responses of CH4 emission to OTC warming in waterlogged versus drained alpine peatlands and identify vegetation composition as a key determinant of peatland CH4 trajectories under warming. These findings highlight hydrological status and vegetation composition as key controls over ecosystem-level responses of peatland CH4 production and oxidation to warming and emphasize the need to represent these controls explicitly in projections of peatland CH4 dynamics.