Effects of Soil Exchangeable Calcium in Promoting the Accumulation of Soil Organic Carbon by Karst Vegetation Restoration

Abstract

This study aims to determine the differences in soil organic carbon (SOC), easily oxidized organic carbon (EOC), particulate organic carbon (POC), mineral-associated organic carbon (MOC), and exchangeable calcium content under different vegetation restoration and to explore the impact mechanism of soil exchangeable calcium on organic carbon accumulation under different particle sizes of aggregates. Two vegetation restoration methods, namely, the artificially managed Chinese prickly ash (CP) and the naturally restored secondary forest (SF), were used for comparison with the cropland (CL). Soil samples were collected at depths of 0–10 and 10–20 cm. Then, the soil-exchangeable calcium content and SOC, EOC, POC, and MOC content of four aggregate fractions were determined. The soil-exchangeable calcium content, SOC, EOC, POC, and MOC content and stocks substantially increased following vegetation restoration. Correlation analysis showed that soil-exchangeable calcium was positively correlated with SOC, EOC, POC, and MOC contents and stocks and had a linear correlation in CL and an exponential correlation in CP and SF. The correlation coefficients can be arranged as SF > CP > CL. Moreover, soil-exchangeable calcium remarkably affected SOC and EOC accumulation in small aggregates in CL and in large aggregates in CP and SF. After vegetation restoration, exchangeable calcium remarkably increased and affected SOC accumulation. In large aggregates, more organic carbon was fixed through calcium ion adsorption, but the carbon fixation ability of CP and SF was limited.