Soil organic carbon stocks increased across the tide-induced salinity transect in restored mangrove region

Blue carbon in mangrove ecosystems contributes significantly to the global carbon cycle. However, large uncertainties maintain in the soil organic carbon (SOC) storage throughout the tide-induced salinity and alkalinity transect in the mangrove restoration region in Southern China. Total 125 soil samples were obtained to detect the SOC content and physicochemical properties. The mean SOC content of each layer ranged from 6.82 to 7.86 g kg(−1), while the SOC density ranged from 2.99 to 11.41 kg m(−2), increasing with soil depths. From different land covers in the study region, the SOC content varied from 4.63 to 9.71 g kg(−1), increasing across the salinity and alkalinity transect, while the SOC density fluctuated from 3.01 kg m(−2) in mudflats to 10.05 kg m(−2) in mangrove forests. SOC concentration was favorably linked with total nitrogen (r = 0.95), and total phosphorus (r = 0.74), and negatively correlated with Cl(−) (r = − 0.95), electrical conductivity (r = − 0.24), and total dissolved solids (r = − 0.08). There were significant logarithmic relationships between SOC content and the concentrations of clay (r = 0.76), fine silt (r = 0.81), medium silt (r = − 0.82), and coarse silt (r = − 0.78). The spatial patterns of SOC concentration were notably affected by soil texture, physicochemical properties, and land-cover type, providing essential reference for future investigations of blue carbon budget in restored mangrove forests.