Dual Effects of Vegetation Restoration Patterns and Soil Depth on the Soil Microbial Residue Carbon Accumulation in a Red Soil Erosion Area of Southern China

ABSTRACT Microbial residue carbon (MRC) is an important source of soil organic carbon (SOC) and plays a vital role in the accumulation and retention of SOC. Vegetation restoration is an effective strategy for restoring degraded lands. However, there are no studies on how the MRC in a profile changes with vegetation restoration. We evaluated MRC (using amino sugars) accumulation and its contribution to SOC at different soil depths (0–20, 20–50, and 50–100 cm) during vegetation restoration in a severely eroded forest (CK), a restored forest (ecological restoration management), an orchard (development management pattern), and a secondary forest (ideal control). Microbial biomarkers were extracted from the soil profiles and used to measure microbial diversity and microbial community composition (using 16S rRNA). Vegetation restoration, soil depth, and their interaction with each other significantly affected the MRC, fungal residue carbon (FRC), and bacterial residue carbon (BRC) contents. The MRC content tended to increase across the four vegetation restoration patterns in the following order: CK (323.25 mg kg −1 ) < orchard (1035.67 mg kg −1 ) < restored forest (2919.01 mg kg −1 ) < secondary forest (6556.72 mg kg −1 ). Furthermore, the contribution of MRC to SOC increased with increasing soil depth in the restored forest. The contributions of total MRC to the SOC content varied from 13.12% to 71.88%. The rapid accumulation of MRC was substantially influenced by the SOC content, total nitrogen content, soil pH, bacterial and fungal diversity, and bacterial and fungal phyla. In conclusion, the patterns of vegetation restoration and soil depth play important roles in the accumulation of soil MRC in red soil erosion areas. These findings are pivotal for improving our mechanistic understanding of the microbial regulation of SOC preservation during vegetation restoration of a degraded ecosystem.