MICROBIAL DRIVERS OF SEDIMENT CARBON CYCLING IN MANGROVES UNDER ENVIRONMENTAL STRESS: A REVIEW

Abstract

Mangroves are important blue carbon ecosystems that store large amounts of organic carbon in biomass and waterlogged sediments. The stability of these carbon stocks is strongly influenced by sediment microbial communities, which regulate organic matter decomposition, carbon fixation, sulphate reduction, methanogenesis, methane oxidation, and other biogeochemical processes controlling carbon turnover and greenhouse-gas dynamics. This narrative review critically synthesises current knowledge on microbial drivers of carbon cycling in mangrove sediments under anthropogenic and climatic pressures. Evidence from mangrove ecosystems is evaluated alongside findings from analogous coastal and terrestrial systems to distinguish well-established processes from context-dependent mechanisms and emerging hypotheses. Current evidence indicates that warming, altered salinity, nutrient enrichment, pollution, hydrological modification, and elevated atmospheric CO₂ can reshape microbial community structure and function, with consequences for carbon mineralisation, greenhouse-gas production, and carbon burial. Particular attention is given to the coupling of sulphate reduction and organic carbon remineralisation, the balance between methanogenesis and methane oxidation, and the contribution of microbial carbon-fixation pathways to sediment carbon accumulation. The review identifies key knowledge gaps, including limited long-term experimental evidence, uncertainty in scaling microbial responses to ecosystem-level carbon outcomes, and the need for stronger mechanistic links between microbial dynamics and blue-carbon stability. Future integration of molecular, biogeochemical, and ecosystem-scale approaches will improve predictions of mangrove carbon cycling under environmental change.