Wetlands are a critical component of the terrestrial carbon cycle. Investigating the variations in plant biomass and soil organic carbon (SOC) among different land-use types within typical wetland reserves can enhance the understanding of wetland carbon cycling dynamics, support China's "Carbon Peak and Carbon Neutrality" goals, and provide theoretical and practical implications for carbon management in terrestrial ecosystems.Focusing on the Danjiang wetland Reserve in Henan Province, this study examined vegetation composition, biomass allocation (above-ground, litter, below-ground), soil profile development, and SOC distribution across three land-use categories: forestland, grassland, and marshland. Results showed that: (1) Biomass allocation characteristics: The total biomass followed marshland>grassland>forestland (understory only), with distinct habitat-specific allocation strategies. Marshland allocated 55% to below-ground biomass, driven by reed rhizome expansion. Grassland prioritized above-ground biomass (51%), reflecting Cynodon dactylon's stem/leaf investment for pioneer colonization. Forestland accumulated 46% in litter biomass due to persistent canopy shedding and slow decomposition rates. (2) Soil profile development characteristics: The development of soil profiles was jointly regulated by vegetation, topography and hydrology. Artificial forest soils showed the greatest depth (70-80 cm) due to human improvement and root activity. Marshland soils reached 40 cm with distinct peat and gley layers (blue-gray) associated with seasonal flooding. Grassland exhibited the shallowest profile (about 30 cm), attributed to erosion and sand deposition. (3) SOC content declined with soil depth. Marshland had the highest SOC content and density, followed by forestland, then grassland. The 0-10 cm surface layer exhibited the greatest SOC concentration and spatial heterogeneity; deeper layers showed more homogenized SOC levels. (4) Grassland root biomass showed a significant positive correlation with surface SOC (P < 0.05), primarily driven by rapid shallow root turnover. Soil bulk density was negatively correlated with SOC, while moisture content was positively correlated with SOC, revealing the promoting effect of moisture conditions on carbon accumulation. This study integrates plant biomass allocation characteristics, soil profile development, and SOC content in wetland reserves to elucidate the intrinsic mechanisms of wetland carbon cycling. The findings fill crucial data gaps in regional soil development and carbon dynamics and provide a scientific basis for optimizing wetland carbon sequestration management.