Plant functional traits and community characteristics jointly shape soil carbon, nitrogen and phosphorus storage in passively restored wetlands following agricultural abandonment

Abstract Wetland reclamation disrupts original biogeomorphic processes, making passive restoration after agricultural abandonment a key near‒natural solution. Served as critical indicators of ecological restoration outcomes, soil organic carbon (TSOC), total nitrogen (TSN), and total phosphorus (TSP) storages are closely linked to plant community succession and functional strategies, but their drivers and influencing pathways remain unclear. This study examined soil functions (TSOC, TSN, and TSP), plant communities, and functional traits in passively restored freshwater wetlands following agricultural abandonment on China’s Sanjiang Plain. Results revealed that TSOC and TSN peaked at 14- and 17-year post-restoration, respectively, then stabilized, while TSP initially decreased before increasing. With extended restoration duration, plant communities showed increased height, coverage and biomass but decreased density and diversity, while functional traits transitioned from acquisitive to conservative strategies. Variance partitioning analysis revealed that soil function dynamics were primarily governed by plant community and functional trait interactions. Random forest models identified key drivers, while structural equation model delineated both direct effects of restoration duration and indirect pathways mediated by plant attributes. Specifically, synergistic declines in specific leaf area (SLA) and plant density enhanced TSOC accumulation. Coordinated reductions in SLA and stem phosphorus content (SPC) increased aboveground biomass (AGB) and TSN but depleted TSP. Furthermore, a trade-off between leaf phosphorus content (LPC) and root-to-shoot ratio (RSR) also modulated TSN dynamics. These findings demonstrate that passive wetland restoration facilitates soil function stabilization, with plant functional traits and community characteristics playing synergistic effects. This mechanistic understanding provides a scientific framework for optimizing restoration strategies.