Iron stimulates greenhouse gas production in Southeast Asian peatlands.

Iron (Fe) acts as a terminal electron acceptor for microbes under oxygen-limiting conditions, leading to organic matter decomposition and emission of carbon greenhouse gases (C-GHG) in peatlands. The underlying molecular mechanism governing this phenomenon is not fully understood. Here, we investigate the role of Fe(III) in C-GHG production using a multiomics approach through a lab-based microcosm experiment on tropical peat collected from three different depths of an Acacia plantation site. Fe(III) amendment leads to severalfold higher production of CO2 and CH4 than unamended setups. Moreover, the gas profile correlates with depletion of carbohydrate compounds in the upper and middle depths, indicating microbial preference for readily fermentable substrates, aligning with increased CO2 production as well as the enrichment of fermentative microbes and genes associated with complex organic carbon degradation. Our study highlights the underestimated role of Fe(III) in carbon transformation and its potential to exacerbate climate change impacts on tropical peatlands.