Abstract: Anthropogenic disturbance is an important driving factor in restoring the degraded systems. The objective of this study is to explore the effects of anthropogenic disturbance on vegetationsoil systems in Symplocos sumuntia secondary forests under three disturbance intensities (slight, moderate, and intensive) in Bifengxia. Plant species composition and diversity (richness index, Simpson index, Shannon index, and Pielou evenness index) in disturbed communities were measured, and the variation of soil properties and their correlation with diversity were evaluated. The results showed that a total of 132 vascular plant species were recorded, belonging to 99 genera and 56 families. Species density and composition showed significant difference among the three communities. With the increases of disturbance intensity, species number in the tree and herb layers decreased, while that of the shrub layer first increased and then decreased. The species diversity of tree layer significantly varied across different intensities of disturbance (P<0.01), decreasing with the increase of the disturbance intensity. No significant difference in species diversity of shrub and herb layers were observed, and their diversity levels were the highest under the moderate disturbance intensity, indicating that disturbance affected mostly the species diversity of the tree layer. The moderate intensity of disturbance enhanced the species diversity in the understory, but was not beneficial to tree species diversity. Disturbance had significant effects on soil moisture, organic matter, and available K contents (P<0.05). Except for soil total P, pH, and bulk density, other soil physicochemical properties (total N, total K, available P, available K, organic matter and soil moisture contents) were the highest in the moderate disturbance, indicating that the moderate intensity of disturbance could improve soil physicochemical properties. Furthermore, there were correlations between soil environmental factors and plant diversity, with the correlations between soil available K, organic matter, available P, and species diversity of community being significant. Our results indicated that the moderate intensity of disturbance could increase species diversity in the understory and improve the soil physicochemical property. Thus, moderate intensity of disturbance was beneficial to the community assembly and ecological restoration of S. sumuntia secondary forest.

Key words: ectomycorrhizal fungi, host plant, symbiosis, nutrient exchange