Warming promotes the use of organic matter as an electron acceptor in a peatland

Peatlands store approximately one-half of terrestrial soil organic carbon (C) and the future of this C in the face of ongoing global change remains a key question in global biogeochemistry. Particularly pressing is the need to understand if this C will remain in peatland soils or be returned to the atmosphere as the potent greenhouse gas methane (CH4) in response to warming. Past work has demonstrated that the microbial reduction of organic matter (OM) as an alternative terminal electron acceptor (TEA) under anaerobic conditions can suppress CH4 production and is a key mechanistic control of peatland CH4 dynamics. Here we show that warming directly enhances rates of potential OM reduction in peatland soils, enhancing acetate availability and allowing for a faster onset of CH4 production. Using soils collected from the ecosystem-scale Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment, we also show that while there were no indirect effects of 2 years of soil warming on potential OM reduction through changes in soil quality, warming-mediated lowering of the water table increased the volume of oxidized OM which will suppress CH4 production following rewetting events.