Microbial organic matter reduction regulates methane and carbon dioxide production across an ombrotrophic-minerotrophic peatland gradient

Abstract

Unraveling the mechanistic controls of methane (CH4) cycling in northern peatland ecosystems is crucial for understanding peatland-climate feedbacks. Growing evidence indicates that the microbial reduction of organic matter as a terminal electron acceptor can be a key regulator of CH4 production in peatlands, but the role of microbial organic matter reduction in different peatlands has not been well explored. Using an electron shuttling capacity assay, we investigated the relationship between the microbial reduction of organic matter and anaerobic CH4 and carbon dioxide (CO2) production in peatland soils in three experiments. In the first experiment, we surveyed the importance of microbial organic matter reduction in six soils representing the ombrotrophic-minerotrophic peatland gradient. In the second experiment, we further explored the reduction of solid-phase organic electron acceptors in a minerotrophic fen and compared these results to previously published values from an ombrotrophic bog (the end members of the initial gradient surveyed). Results from these experiments suggest that microbial organic matter reduction suppresses CH4 production, especially in ombrotrophic peat soils, likely helping to explain low CH4 production in bog-like soils. In contrast, the pool of oxidized organic matter was quickly reduced in minerotrophic peat soils which subsequently exhibited higher rates of CH4 production. In the final experiment, we investigated the effect of temperature on microbial organic matter reduction in the same ombrotrophic bog soil, demonstrating that warmer temperatures resulted in both a faster reduction of solid-phase organic matter and an apparent increase in the size of the organic electron acceptor pool that can be reduced by microbes. Future work should explore the drivers of the observed differences in microbial organic matter reduction in different peatland soils to provide a stronger mechanistic explanation for how this process will regulate peatland greenhouse gas dynamics in the face of global change, including increases in temperature.