Abstract: Aims After the control of Spartina alterniflora, two distinct management approaches—preserving bare mudflats and planting mangrove forests—have been found to influence wetland soil microorganisms and carbon cycling processes. However, there remains a significant gap in the systematic understanding of how these two management strategies affect the structure and function of soil fungal communities, the distribution and turnover of organic carbon components, and consequently impact carbon pool activity and management efficiency. Methods Employing high-throughput sequencing (ITS1) and carbon fractionation techniques, we systematically analyzed differences in fungal community composition between bare flat wetlands and mangrove-restored wetlands as well as their dynamic associations with distinct stability classes of organic carbon components after S. alterniflora management. Important findings The results demonstrated that Ascomycota and Basidiomycota remained the dominant fungal phyla in mangrove-replaced wetland soils, with combined average relative abundance reaching 65%. The predominant genera shifted to Leucosporidium and Phaeosphaeria, whose distributions were significantly regulated by soil moisture content, bulk density, and electrical conductivity. FUNGuild functional prediction revealed that saprotrophic fungi maintained the highest relative abundance (15.4%-47.8%) before and after mangrove replacement, with soil saprotrophs-undefined saprotrophs and arbuscular mycorrhizal fungi predominating in functional groups. The relative abundance of soil-borne plant pathogens decreased post-replacement. Compared to bare flats, mangrove-replaced wetlands exhibited reduced organic carbon content but showed varying increases in Carbon Pool Activity Index (CPAI) and Carbon Pool Management Index (CPMI). The alpha diversity of the fungal community emerged as the primary factor influencing easily oxidizable organic carbon (EOC) content, accounting for 50.8% of variance. Facultative saprotrophic fungi significantly enhanced carbon turnover efficiency by driving recalcitrant organic carbon transformation (p<0.01). Based on the above, this study demonstrates that mangrove replacement effectively promotes the transformation of soil organic carbon from recalcitrant to labile forms by enhancing the functional dominance of saprophytic fungi, consequently altering the CPMI. These findings advance theoretical understanding of the interaction mechanisms between wetland organic carbon components and microbial communities, thereby offering scientific foundations for sustainable coastal wetland conservation.

Key words: mangrove, fungal communities, soil organic carbon stability, carbon pool management, coastal wetlands