Electromethanogenesis underpins the methane production in a Tibetan wetland

Wetlands are a significant source of methane, a potent greenhouse gas that contributes to global warming. Acetate and H 2 /CO 2 are generally considered the dominant precursors for methane formation, while H 2 , generally considered as the electron donor, is considerably lower in wetlands. This work investigated alternative reductive mechanisms of methanogenesis in the soil microcosms of Zoige wetland on Tibetan Plateau. Carbon monoxide inhibition of hydrogenase combined with isotope tracing experiments indicated only 2.9%-12.5% of the wetland H 2 was used in methanogenesis. Electron shuttles (biochar and magnetite) promoted methane production, and electrochemical experiments detected current generation from bacteria and current consumption coupled to methane production, confirming that electromethanogenesis occurred in the Zoige wetland and contributed 27.7%-50.9% of CH 4 production. Moreover, electromethanogenesis exhibited 2.6-16.1-fold higher CO 2 - and methanol-reductive methanogenic efficiencies than using H 2 . Uncultured Rice Cluster Ⅱ methanogens and a family of H 2 -dependent methylotrophic methanogen called Methanomassiliicoccaceae were enriched in electrochemical microcosms. Remarkably, oxidized anthraquinone-2,6-disulfonate decreased methane production. This work verifies the role of electromethanogenesis in a Tibetan wetland and provides a potential strategy for reducing methane emission.