Divergent pathways of shaping soil organic carbon accumulation in a riparian wetland modulated by vegetation type and microbial‑iron coupling

Although vegetation restoration with increased species diversity benefits soil organic carbon (SOC) accumulation in wetland ecosystems, however, the mechanisms involved and coupling plant-microbe-mineral interactions under different vegetation regimes and flooding gradient remain insufficiently explored. Here, 42 plots were selected in a typical Yellow River wetland with sandy soil, where the changes in microbial life history strategy, plant- and microbial-derived components, and Fe-mediated dual oxidation/mineral protection in SOC accumulation were assessed in response to different vegetation types, including an unplanted floodplain. The restoration significantly increased SOC (1.06–7.58 g kg −1 ), total microbial necromass C (MNC, 12.8–24.3 % of SOC) and lignin phenol contents. High-biomass woody and graminoid species, particularly Phragmites australis exhibited high bacterial and fungal K/r ratios, enhancing accumulation from lignin-derived and fungal necromass, thereby facilitating the development of mineral-associated organic carbon (MAOC, ∼66 % of SOC) for long-term stabilization. Concurrently, the negative correlation between MNC (lignin phenols) and its relative contribution to the formation of SOC highlights the MAOC formation or the accumulation of other recalcitrant compounds. In contrast, low-biomass herbaceous species favor bacterial r-strategists that accelerate particulate organic carbon (POC) turnover via heightened hydrolytic enzyme activities, while stimulating Fe(II)-derived •OH oxidation, promoting CO₂ emission and carbon pool lability. Additionally, iron in waterlogged systems couples anaerobic preservation of DOC with the highest CO₂ emissions through Fe-mediated oxidation. Our study demonstrates that plant types regulate microbial life history strategies, thereby influencing SOC dynamic and turnover, offering a clear mechanism for enhancing carbon sequestration and stability through strategic vegetation management. • Recalcitrant lignin phenols and MNC accumulate during wetland restoration • K-strategist microbes enhance MAOC formation in woody/graminoid systems • The contribution of FNC to SOC gradually increases with vegetation restoration • •OH oxidation of POC drives CO₂ emission in herbaceous systems • Fe mediates both DOC preservation and oxidative carbon mineralization.