Saturation‐Constrained and Spatially Heterogeneous Soil Organic Carbon Sequestration Following Bare Land Restoration in China

Abstract

Soil organic carbon (SOC) sequestration represents a critical nature‐based strategy for atmospheric CO ₂ mitigation. Yet, the magnitudes and dynamics of SOC accrual following bare land restoration have not been rigorously quantified at a large scale. By integrating field‐based observations with a spatially explicit machine learning framework, this study systematically evaluated the drivers, optimization pathways and SOC sequestration potential of bare land restoration across China. Results reveal that SOC accrual follows a distinct three‐stage pattern: rapid accumulation (0–17 years), a restoration bottleneck (17–30 years), and slow accumulation toward SOC saturation (>30 years). This process is primarily driven by baseline SOC, with greater accrual in low initial SOC regions. Projections indicate a nonlinear trajectory, reaching a plateau around 2,080 (approximately 55 years post‐restoration). By 2,100, cumulative SOC sequestration in the top 30 cm is projected at 6.1 ± 0.9 Pg C, concentrated in humid regions. Notably, the 0–5 cm layer responds rapidly, whereas the 15–30 cm horizon exhibits a temporal lag but sustained growth. Uncertainty analysis indicates that spatial heterogeneity dominates total variance (79.5%–87.8%), whereas climate scenario uncertainty is comparatively limited. These findings demonstrate that SOC sequestration is a spatially heterogeneous and saturation‐constrained process, emphasizing the importance of site‐specific restoration strategies for effective climate mitigation.