Abstract: To investigate the characteristics and stability of soil carbon pools in mangroves restored through the conversion of aquaculture ponds to wetlands, three planted mangrove communities (Avicennia marina, Rhizophora stylosa, Bruguiera sexangula) were selected in the Xiaohai Lagoon of Wanning City, Hainan Province. Soil physicochemical properties, different organic carbon fractions and carbon pool stability indices in the 0-20 and 20-40 cm soil layers were measured to reveal the differences and controlling factors. The results showed there were significant differences in soil physicochemical properties among the three communities. Soil organic carbon (SOC) content in the 0-20 cm layer was highest in the A. marina community, while in the 20-40 cm layer, it was highest in the R. stylosa community. Total SOC storage (SOCS) in the 0-40 cm depth followed the order: B. sexangula (7.05±0.3 Mg C·hm^-2) < A. marina (12.93±1.02 Mg C·hm^-2) < R. stylosa (15.33±1.55 Mg C·hm^-2). The ratios of particulate organic carbon (POC) to mineral-associated organic carbon (MAOC) varied significantly among soil layers and plant communities. The maximum ratio was observed in the 20-40 cm soil layer of B. sexangula community, indicating the weakest stability of soil organic carbon in this layer. R. stylosa had the highest LOC/SOC, DOC/SOC, and MBC/SOC ratios in the surface layer, reflecting faster organic carbon turnover. Soil bulk density and pH were the key factors influencing soil organic carbon fractions. RDA results showed that soil bulk density had the highest explanatory power (R²=0.793, P<0.01), followed by soil pH (R²=0.568, P < 0.01). In conclusion, in the early stage of converting fish ponds to wetlands, there are significant differences in soil carbon pools and organic carbon stability among different mangrove communities. A. marina and R. stylosa communities demonstrated a particularly prominent short-term advantage in soil carbon sequestration. These results provide a scientific basis for ecological restoration and carbon sink management of coastal wetlands.

Key words: