Background Land-use changes significantly affect soil stability and carbon sequestration in karst regions, particularly in small watersheds, which exhibit a heightened response. This study investigates the impact of various land uses on soil aggregate stability and organic carbon distribution in the karst area of Hubei, specifically within the Xialaoxi watershed. The goal is to enhance our understanding of soil structure and the potential for carbon sequestration in these ecosystems.

Methods In cypress forest (CF), vegetable farmland (VF), stone terraced field (ST), stone terraced forest (SF), and natural forest (NF), three sample plots were randomly established in each area. Within each plot, soil samples from the original surface layer (0 - 10 cm) were collected using the five-point sampling method. Mechanical stability of soil aggregates and water stability were determined using both dry and wet sieving methods. Organic carbon and active organic carbon contents of the soil in each plot were also measured. Correlation and redundancy analysis methods were employed to thoroughly analyze the impact of soil properties on soil stability.

Results 1) Under different land use types, the proportion of > 2 mm mechanically stable aggregates was the highest, and it decreased as the particle size decreased. In forest land, the proportion of > 2 mm water-stable aggregates was the highest, while in farmland, it was the opposite. 2) The mechanical stability aggregates and water stability aggregates of the forest land have higher M_WD and G_MD than those of the cultivated land. The variation types of fractal dimension D and soil erodibility K are exactly opposite. Among them, the D and K values of the CF site are the smallest, indicating that the CF site has higher soil structure stability and stronger soil erosion resistance. 3) Soil aggregate SOC content is significantly higher in forests than in farmland, with the highest SOC content in aggregates > 0.25mm. The trend of soil aggregate LOC content is similar to that of aggregate SOC. 4) Relevance analysis and redundancy analysis results show that the SOC content of soil aggregates of various particle sizes is significantly negatively correlated with fractal dimension and soil erodibility, while it is significantly positively correlated with stability indicators M_WD and G_MD. The content of water-stable aggregates > 2 mm has the most significant impact on soil water stability, indicating that soil organic carbon plays a crucial role in both soil aggregate stability and soil erosion resistance.

Conclusions These results indicate that the risk of soil erosion in the Xialaoxi watershed of the western Hubei karst region is relatively high, particularly in agricultural areas. The implementation of artificial afforestation measures can significantly improve soil structure and enhance the capacity for soil carbon sequestration. We should prioritize adjusting land use and implementing artificial afforestation and conservation tillage practices to mitigate the risk of soil erosion in the study area. The relevant research findings can serve as a valuable reference for the sustainable development of land use improvements and ecological protection in the small watersheds of western Hubei karst region.