Investigating the relationship of soil aggregate stability with the organic carbon in the aggregate and its response to land use change is conducive to the estimation of soil carbon sink potential, improvement of rocky desertification, and rational land use in karst areas of Southwest China. In order to explore the effects of land use change on the composition and stability of soil aggregate stability as well as the content of aggregate organic carbon, the soil (0-30 cm) of five land use types (secondary forest, pomelo forest, paddy field, pepper forest, and dry land) was selected as the research object. The characteristics and correlation of soil aggregate components and organic carbon under different land use patterns were obtained, and the contribution of soil aggregates to the change in organic carbon after land use change was calculated. The results showed that the macroaggregates in the surface soil (0-15 cm) of the secondary forest, pomelo forest, and paddy field were 63.32%, 52.38%, and 47.77%, respectively, which were significantly higher than that of dry land (23.70%), as was also seen in the lower layer (15-30 cm). The geometric mean diameter (GMD) and mean weight diameter (MWD) of soil aggregates in the secondary forest, pomelo forest, and paddy field were significantly higher than those in dry land. In the surface soil, the organic carbon of the secondary forest and paddy field was significantly higher than that of other land use patterns. By contrast, in the lower soil layer, only the organic carbon of the paddy field was significantly higher than that of the others. Under different land use patterns, the organic carbon content of aggregates followed the same order of macroaggregates > microaggregates > silt and clay, indicating that macroaggregates allowed soil organic carbon to accumulate, whereas silt and clay did the opposite. According to correlation analysis, the content of soil macroaggregates was significantly positively correlated with GMD, MWD, and soil aggregate organic carbon, suggesting that the increase in soil macroaggregates could improve the stability of soil aggregates and store more soil organic carbon. Further, as land use change may have significantly affected the soil aggregate, moderate development of forestry and paddy cultivation is suggested to improve the soil carbon sequestration potential in the karst area of Southwest China.
Keywords: karst area; land use change; soil aggregates; soil organic carbon （SOC）; stability.