1. Mangrove forests are among the most productive blue carbon (C) ecosystems. While mangrove restoration is recognized for its potential to increase coastal blue C storage, its effects on soil organic C (SOC) stability and sources remain poorly understood. 2. Here, we examined the effects of mangrove restoration on SOC fractions and explored the relative contributions of plant versus microorganisms to these fractions. Specifically, we assessed the contents of particulate organic carbon (POC), coarse mineral-associated organic carbon (cMAOC), fine mineral-associated organic carbon (fMAOC) and two biomarkers (lignin phenol and amino sugar) across different restored vegetation zones in a typical mature mangrove wetland. 3. Our results showed that mangrove restoration significantly increased the contents of all SOC fractions: POC (increasing by 39.90%–178.15%), cMAOC (27.98%–134.03%) and fMAOC (96.39%–731.56%). Notably, restoration primarily increased SOC through the accumulation of fMAOC (explaining 59.07% of SOC variation). We also found that Fe-bound C (17.10%) predominated over Ca-bound C (6.84%) in fMAOC accumulation, likely due to redox changes following restoration. More than 65% of MAOC originates from plant residues, with a smaller proportion derived from microbial necromass. These findings emphasize the predominant role of minerals in stabilizing plant-derived organic C over microbial-derived organic C in mangroves. 4. Overall, this study highlights the potential of mangrove restoration not only to increase SOC sequestration but also to enhance its stability through mineral-organic interactions, positioning mangrove restoration as a valuable nature-based solution for climate change mitigation.
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