Abstract: Coastal wetlands are biogeochemical hotspots for the global sulfur cycle. Driven by the combined influences of hydrodynamic processes, multiple material inputs, and pronounced redox gradients, sulfur undergoes complex valence-state variations and speciation transformations in coastal wetlands. We systematically summarize research advances on sulfur cycling in coastal wetlands in nearly four decades, with a focus on the major forms and classification of inorganic sulfur pools. We discuss the impacts and underlying mechanisms of microorganisms, plants, key physicochemical environmental factors, and anthropogenic disturbances on inorganic sulfur transformation and mobility. We further examine the role of sulfur cycling in mediating carbon source-sink processes in coastal wetlands. Firstly, sulfate reduction regulates sedimentary carbon transformation by mediating anaerobic organic matter mineralization. Secondly, organic matter sulfurization, sulfur oxidation-driven chemolithoautotrophic dark carbon fixation, and iron-sulfur mineral formation and associated mineral protection of organic carbon collectively contri-bute to carbon stabilization and burial. Thirdly, sulfur cycling regulates coastal wetland greenhouse gas budgets by modulating the production and emission processes of CO₂ and CH₄. Future research should focus on the sulfur cycle response mechanisms under global change, multi-element coupling processes, and the construction of sulfur-carbon cycle models. This review would provide a scientific basis for enhancing ecosystem management and blue carbon sequestration in coastal wetlands and supporting the restoration and maintenance of ecosystem services under ongoing global climate change.

Key words: coastal wetland, sulfur cycling, sulfur speciation and transformation, sulfur-carbon coupling, biogeochemical process