Comprehensive Benggang control promotes the recovery of soil organic carbon fractions and carbon sequestration potential

Benggang is a severe collapsing-gully erosion landform in the granite-derived red-soil region of southern China. Although comprehensive Benggang control integrating engineering measures, vegetation restoration, and management has improved the erosion environment and promoted vegetation and soil recovery, the recovery patterns of soil organic carbon (SOC) fractions remain unclear. Using a restoration chronosequence consisting of the untreated, active Benggang site, 6-, 10-, and 23-year-old restoration sites (R1, R2, and R3, respectively), and a secondary Pinus massoniana forest as the reference, we investigated the spatiotemporal patterns of SOC fractions and mineral-associated organic carbon (MAOC) saturation metrics. Comprehensive Benggang control produced spatially complementary carbon-sequestration patterns. In the middle Benggang section of R3, SOC and MAOC concentrations in the 0–20 cm depth interval reached 8.4 and 5.7 g kg −1 , respectively, whereas the MAOC saturation degree in the 20–40 cm depth interval reached 23.3 %. In the lower Benggang section of R3, fine-particle content in the 20–40 cm depth interval reached 62.9 %, while the MAOC saturation deficit remained 19.4 g kg −1 . Random forest analysis identified aggregate stability as the dominant predictor of particulate organic carbon (POC) and MAOC, with relative importance values of 76.8 % and 29.2 %, respectively; available and total phosphorus contributed 22.5 % and 16.7 % to MAOC prediction. Structural equation modeling indicated direct positive effects of soil structure on POC (path coefficient = 0.72) and soil phosphorus on MAOC (path coefficient = 0.47). These quantified results provide a scientific basis for precision management and the enhancement of carbon-sink function in Benggang systems.