Effects of agricultural abandonment on soil aggregation, soil organic carbon storage and stabilization: Results from observation in a small karst catchment, Southwest China

Soil organic carbon (SOC) storage and stabilization under land-use change, including agricultural abandonment, are critical for the recuperation of soil productivity and feedback to climate change. A space-for-time substitution approach was applied to investigate the responses of soil aggregation, SOC storage and stabilization to agricultural abandonment in a small karst catchment in Southwest China. Soil aggregate distribution, SOC concentration and delta C-13 composition in bulk soils and different-sized aggregates in soil profiles under cropland, abandoned cropland and native vegetation land were determined. The results showed that SOC storage and soil aggregation were significantly reduced in the surface soils of croplands compared to those under native vegetation; SOC storage was slowly restored in 3-8 years abandoned cropland, but soil aggregation was rapidly recovered. The rapidly recovered macro-aggregates controlled the recuperation of SOC storage after agricultural abandonment because most SOC (64%-83%) was sequestrated by macro-aggregates. The relationships between SOC concentrations and delta C-13 values in different-sized aggregates of surface soils could indicate a change in SOC stabilization under land-use change. In this study, SOC stabilization was gradually enhanced following agricultural abandonment. These results suggest that soil aggregation, SOC storage and stabilization are recovered following agricultural abandonment in the karst region.