Effects of soil microorganisms on aggregate stability during vegetation recovery in degraded granitic red soil areas

Soil aggregates determine the soil structure, and the various cementitious substances produced by microorganisms can affect the composition and stability of soil aggregates. Currently, the characteristics of soil microorganisms and the mechanisms of aggregate stability during vegetation restoration in granite erosion areas remain unclear. In this study, the following five vegetation restoration stages in erosion zones were examined: bare land (LD), grassland (CD), grassland-shrub transition land (CG), shrubland (GM), and secondary forest (CS). By analyzing the relationships among the microbial community structure, aggregate stability, and soil physicochemical properties, the key factors influencing soil aggregate stability were identified. The findings revealed that with vegetation restoration, the stability of soil aggregates (mean weight diameter (MWD) and geometric mean diameter (GMD)) and the content of water-stable aggregates larger than 0.25 mm (WR0.25) increased, and the stability was greater in the soil surface layer than in the subsurface layer. High-throughput sequencing demonstrated a notable increase in the Shannon diversity index and richness index of the soil microorganisms in the soil surface layer compared with those at the LD stage. Pearson correlation analysis revealed positive associations between the soil aggregate stability and the abundance and diversity of soil bacteria, archaea, and nutrients such as soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and available nitrogen (AN). The redundancy analysis results indicated that the relative abundance of key phyla such as Thermoplasmatota, Ascomycota, Actinobacteriota, and Proteobacteria, along with the alpha diversity of bacteria and archaea in the soil surface layer, accounted for 85.90 % of the overall formation and stabilization of soil aggregates with particle sizes of 2 mm and 1-2 mm. Notably, Actinobacteriota was the primary contributor, explaining 82.6 % of the total variance in the soil aggregate stability. Actinobacteriota also significantly increased the soil nutrient content and aggregate stability. These findings provide an important scientific basis for soil quality improvement in granite erosion areas.