Mangrove ecosystems are globally important blue carbon reservoirs, yet the processes controlling soil organic carbon (SOC) stabilization during restoration remain insufficiently understood. This study investigated how estuarine setting, restoration strategies, and soil depth regulate particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) and their contributions to SOC in Qinglan Harbor, southern China. Compared with far-estuary sites, near-estuary sites presented higher POC and MAOC contents, with increases of 22.6% and 51.5%, respectively, whereas their relative contributions to SOC did not differ significantly. The restoration strategy significantly affected POC and SOC partitioning, with natural forests having higher POC contents than active and passive restoration sites did (234.6% and 213.8%, respectively), along with higher POC/SOC and lower MAOC/SOC ratios. Soil depth alone had no significant effect on SOC fractions, but its interaction with estuarine setting influenced POC distribution, with POC increasing with depth in the near-estuary but decreasing in the far-estuary. Vegetation structure, soil properties, and microbial diversity jointly regulated SOC fractions. POC increased with plant height and soil electrical conductivity but decreased with diameter at breast height and bacterial richness, whereas MAOC showed contrasting relationships with vegetation structure. Structural equation modeling indicated that both POC and MAOC were positively associated with SOC, with standardized path coefficients of 0.86 and 0.43, respectively. Environmental factors influenced SOC primarily through indirect pathways mediated by SOC fractions, whereas microbial diversity had a weak negative indirect effect. These results highlight the importance of SOC fractions in understanding carbon dynamics during mangrove restoration.
Wang et al. (Sat,) studied this question.