Objective This study aimed to investigate the effects of different restored vegetation types on soil structural stability in the Eastern Qinling Mountains, in order to provide a scientific basis for regional vegetation restoration and ecological management.

Method Seven typical vegetation types (Pinus tabulaeformis Carr., Quercus variabilis Blume, Pinus tabulaeformis-Quercus variabilis mixed forests, Platycladus orientalis (L.) Franco, Robinia pseudoacacia L., grassland and farmland) were selected in the Eastern Qinling Mountains. The vegetation community characteristics of the sample plots were investigated using the quadrat method. Soil samples were collected from three depths (0 - 5 cm, 5 - 20 cm, and 20 - 40 cm), and the composition of water-stable aggregates of different particle sizes was determined. The soil aggregate stability under different vegetation types was evaluated using soil aggregate stability indicators, including mean weight diameter (MWD), content of water-stable aggregates ≥ 0.25 mm (R_0.25), fractal dimension (D), and aggregate destruction rate (PAD). Correlation analysis was applied to examine the influence of species diversity on soil aggregate stability in combination with vegetation coverage and plant diversity indices.

Result ① The typical restored forest and grassland vegetation in the Eastern Qinling Mountains significantly improved soil structure. In the 0 - 40 cm soil layer, the Pinus tabulaeformis-Quercus variabilis mixed forests exhibited the highest proportions of large-sized aggregates (≥ 1 mm), mean weight diameter (MWD), and R_0.25 values, with significantly greater soil structure stability compared to monoculture forests and farmland (P < 0.05). ② Soil aggregate stability decreased with increasing soil depth. The highest aggregate stability was observed in the surface layers (0 - 5 cm) of forested and grassland areas. The mixed forests and Platycladus orientalis (L.) Franco maintained a notable positive effect on deep soil layers (20 - 40 cm). ③The Pinus tabulaeformis Carr. and Platycladus orientalis (L.) Franco demonstrated the highest levels of species richness, diversity, and evenness. Forest ecosystems outperform agricultural land in terms of biodiversity conservation and ecological function restoration. ④ Species diversity was positively correlated with large-sized aggregates (≥ 1 mm) and significantly negatively correlated with small-sized aggregates (< 0.25 mm) (r = 0.72 - 0.80), indicating that higher species diversity contributes to enhanced soil structural stability.

Conclusion The Pinus tabulaeformis-Quercus variabilis mixed forests in the Eastern Qinling Mountains significantly enhanced the deep soil aggregate stability through high species diversity and were the preferred vegetation types for regional ecological restoration. In contrast, farmland suffered from soil structure degradation due to low biodiversity and frequent farming disturbances, leads to soil structure degradation. It is recommended that priority be given to mixed forests and Platycladus orientalis (L.) Franco in ecological management strategies to improve soil quality and enhance ecosystem service functions.