The carbon cycle of wetland ecosystems has important influences on a more general terrestrial ecosystem carbon balance, and it is sensitive to changes in global climate and local land use. However, our mechanistic understanding of soil carbon sequestration in wetland ecosystem is incomplete. There have been many studies on soil carbon sequestration in wetland ecosystems, but most of them focused on the abiotic drivers. In an effort to elucidate the importance of biotic factors in influencing the response of ecosystem carbon cycles to global changes, we reviewed the influences of plant functional traits and functional trait diversity on the soil carbon sequestration of wetland ecosystems. We first briefly discuss the concepts of plant functional traits and functional trait diversity. Then we review published literature and reach a broad conclusion that plant functional traits can affect soil carbon cycling through altering carbon inputs and loss to and from soils. More specifically, plant growth rate can be related to the amount of carbon forms that plants return to soil, and their subsequent fate in soil. The allocation of carbon and nutrients between plant organs also affects soil carbon sequestration. Higher root/shoot ratios may indicate increased soil carbon sequestration potential, as root litter generally appears to be of more recalcitrant carbon pool than that of shoots. Soil carbon mostly originates from decaying aboveground and belowground plant tissue, but root exudates are also an important source of carbon input to soil. Plant traits related to forming mutualistic symbioses are important for soil carbon input, as they typically increase carbon assimilation through enhanced acquisition of limiting resources. Plant functional traits strongly influence litter decomposability, soil respiration, carbon immobilization and leaching. High lignin content and other recalcitrant carbon forms enhance soil carbon sequestration because of their long residence time in soil. In waterlogged conditions, the lost rates of methane and carbon dioxide to the atmosphere from soil depend on the type of aerenchyma of roots. Plant traits that alter the soil′s abiotic conditions can have strong effects on soil carbon sequestration, such as plant canopy characteristics, which control microenvironment conditions related to carbon mineralization and leaching. We explored possible approaches by which the functional diversity directly and indirectly influences ecosystem carbon cycle through dominant species role, plant specific interactions and plant-microorganism interactions. The relative abundances and productivities of the predominant plant functional types and their traits appear to be the principal factor determining soil carbon dynamics. Specific plant trait compositions also influence soil carbon dynamics through complementarity or facilitation of plant traits at community level. However, there remains much uncertainty over the extent that trait interactions among plant species might influence carbon inputs and losses, because such interaction effects appear to be context dependent. Plant trait composition may influence soil decomposer diversity through the diversity of substrates and habitats, and decomposer diversity in turn can affect soil carbon cycling through functional complementarity. Finally, we proposed several future avenues for research on the effects of plant functional traits and functional diversity on soil carbon sequestration of wetland ecosystems.