Recovery in soil carbon stocks but reduced carbon stabilization after near-natural restoration in degraded alpine meadows

Near-natural restoration is acknowledged as an effective strategy for enhancing soil organic carbon (SOC) sequestration in degraded grasslands. However, the alterations in SOC fractions, stability, and relative sequestration capacity after restoration of degraded alpine meadows remain uncertain. In this study, we utilized the degraded alpine meadows on the northeastern edge of the Tibetan Plateau as a research area, with grazing as the control (CK) and restoration of 20 years of banned grazing (BG) and growing season resting grazing (RG). We analyzed the characteristics of SOC, SOC fractions, recalcitrant index (RI), and relative capacity of soil C sequestration (SCS_capacity) under near-natural restoration measures. The objective of this study was to assess the recovery of SOC following near-natural restoration. The results showed that soil water content (SWC), SOC, soil total nitrogen (TN), and soil total phosphorus (TP) increased, while bulk density (BD) decreased in the degraded alpine meadow after near-natural restoration. In addition, near-natural restoration led to significant increases in particulate organic carbon (POC), readily oxidizable carbon (ROC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) content (P < 0.05). The SOC stock significantly increased, while the RI decreased. Compared to RG, BG had a greater increase in SOC stock. The study showed that 20 years of near-natural restoration in degraded alpine meadows mainly enhanced soil active carbon pools, while short-term restoration did not increase soil carbon stability. Therefore, avoiding re-exposure to overgrazing is essential to maintaining the restoration effect.