Contrasting fates of detritus in mangrove sediments: Microbial trade‐offs between carbon storage and greenhouse gas emissions

Abstract Mangroves are known as important carbon storage hotspots, yet their net climate benefit can be offset by large greenhouse gas emissions. In this study, we conducted a 1‐yr in situ incubation coupled with high‐resolution molecular and microbial analyses to elucidate the fate of two major types of mangrove detritus, including leaves ( Kandelia obovata and Sonneratia apetala ) and macroalgae ( Ulva prolifera ), via microbial metabolism. Approximately 50% of the added organic carbon from both sources was mineralized to CO 2 , while 7.5% (leaves) and 9.7% (macroalgae) were emitted as methane (CH 4 ). Around 33.8% of the leaf‐derived and 2.1% of the macroalgae‐derived organic carbon contributed to longer‐term carbon storage. CH 4 emissions from leaf litter offset approximately 11.1% of the net ecosystem productivity and were positively correlated with molecular formulas assigned to the aliphatic‐like group and with sulfur‐ and phosphorus‐containing molecular formulas. CH 4 production was initially dominated by methylotrophic methanogenesis (mostly Methanolobus ), followed by more diverse pathways associated with Methanosarcina . Our results demonstrate that different types of mangrove detritus have distinct effects on sediment biogeochemistry and greenhouse gas emissions and highlight the need to account for both CO 2 and CH 4 emissions when assessing the climate benefits of mangrove ecosystems.