Depth-dependent responses of the soil bacterial community under vegetation restoration in soil erosion areas of southern China

Soil bacterial communities play a crucial role in the evaluation of soil ecosystem stability. Vegetation restoration is a key determinant of soil bacterial communities in areas affected by soil erosion. However, it remains unclear how the structure and diversity of soil bacterial communities vary with soil depth. In this study, we collected soil samples from 0 to 10 cm, 10 to 20 cm, 20 to 30 cm, and 30 to 40 cm depths in vegetation restoration sites located in typical soil erosion areas in China. We compared and analyzed the differences in bacterial community characteristics among different soil depths, using untreated areas as controls. Compared to the untreated areas, the abundance of soil bacteria in the 0-10 cm, 10-20 cm, and 20-30 cm depths of the vegetation restoration sites increased by 1.63, 1.04, and 1.29 times, respectively. Furthermore, vegetation restoration enhanced soil bacterial diversity at the 0-10 cm, 10-20 cm, and 20-30 cm depths. Soil organic carbon (OC) was the main explanatory factor (53.50%, p = 0.000) for the decrease in soil bacterial diversity with soil depth. Additionally, after vegetation restoration in soil erosion areas, the dominant bacterial community composition shifted from Chloroflexi to Actinobacteria at the 0-10 cm, 10-20 cm, and 20-30 cm depths and to Proteobacteria at the 30-40 cm depth. The differences in soil bacterial communities among different soil depths were primarily driven by soil total nitrogen (TN) content, which explained up to 34.5% of the variation. In conclusion, in the subsequent management of vegetation restoration sites, increasing OC and TN content can enhance soil bacterial diversity, improve bacterial community composition, and ultimately enhance the stability of soil ecosystems.