Organic Matter Redox Status Predicts Methane Production in Boreal Peatland Ecosystems

Abstract Boreal peatlands are important locations of carbon storage, but the mechanisms controlling methane (CH 4 ) production in these ecosystems are not fully understood. Reduction of redox-active organic matter (RAOM) is one understudied mechanism where microbes use solid-phase (i.e., peat) organic matter as a terminal electron acceptor in anaerobic respiration. RAOM reduction suppresses methanogenesis due to energetic favorability and is often considered as an explanation for why certain peatland ecosystems produce less CH 4 than expected after accounting for other electron acceptors. Given the role of RAOM in regulating CH 4 production, we compiled datasets from boreal peatlands in the USA that quantified RAOM redox state using an electron shuttling capacity (ESC) assay and evaluated how RAOM reduction predicted CH 4 production in laboratory and in situ field incubations. Across all laboratory incubations, CH 4 production linearly increased as RAOM was reduced, explaining 20% of average CH 4 production over time. Predictive power was stronger in bogs than fens, although both produced negligible CH 4 (< 0.01 μmoles) until RAOM reduction reached a certain threshold (~ 20 μmoles e − /g dw peat). In field incubations, CH 4 production also linearly increased as RAOM became more reduced, explaining 60% of average CH 4 production. Overall, RAOM redox state was a good predictor of CH 4 production across boreal peatland ecosystems, consistent with the growing evidence suggesting that RAOM is the major terminal electron acceptor for anaerobic respiration in peatlands. Our work demonstrates that incorporating RAOM dynamics into peatland carbon cycling frameworks can help improve predictions of present and future CH 4 emissions.