Abstract: In recent years, the density of Vitex negundo shrubs in Northwest Liaoning has increased year by year and invaded grassland, aggravating the shrub encroachment. To explore the effects of V. negundo encroachment on soil stability and erosion resistance of grasslands, we selected four grassland types including non-encroached grassland and lightly, moderately and severely encroached grasslands in Northwest Liaoning. We analyzed the changes in soil physicochemical properties, and aggregate stability, as well as soil erodibility and its influencing factors. The results showed that with the intensification of shrub encroachment, soil porosity and soil organic matter increased significantly. They rose from 26.0% and 14.89 mg·kg^-1 in non-encroached grassland to 45.8% and 33.15 mg·kg^-1 in severely encroached grassland, respectively. By contrast, the mean weight diameter and geometric mean diameter of soil aggregates decreased markedly, declining from 1.55 mm and 1.34 mm in non-encroached grassland to 0.92 mm and 0.63 mm in severely encroached grassland, respectively. Soil erodibility factor (K value) in severely encroached grasslands was significantly 93.1% higher than that in non-encroached grasslands, indicating that shrub encroachment weakened soil erosion resistance. Structural equation model analysis revealed that shrub encroachment exerted a significant direct positive effect on soil K value, and indirectly affected the K value by regulating soil organic matter content, thereby decreasing soil erosion resistance of grasslands in Northwest Liaoning.

Key words: Northwest Liaoning, Vitex negundo, shrub encroachment, soil aggregate stability, erosion resistance