Slow recovery of stable carbon constrains long‐term soil carbon restoration in China's restored wetlands

Wetland restoration is widely implemented to rebuild soil organic carbon (SOC); however, success is still commonly assessed using bulk SOC, which integrates carbon pools with distinct turnover times and stabilization mechanisms, and may therefore misrepresent the recovery of stable carbon. To address this limitation, we compiled a national‐scale dataset of restored wetlands across China (452 paired comparisons from 43 sites) to quantify the recovery trajectories of labile organic carbon (LOC) and recalcitrant organic carbon (ROC), with ROC defined as SOC minus LOC and used as a proxy for the relatively stable SOC pool. LOC and ROC showed distinct associations with restoration drivers: LOC recovery was closely associated with plant biomass and gross primary productivity, whereas ROC recovery was primarily constrained by clay content, pH and salinity. After 60 years of restoration, LOC recovered to approximately 50% of natural wetland levels, ROC reached only ~37%, and overall SOC recovered to ~39%; all three pools exhibited pronounced deceleration within the observed restoration period. Recovery magnitudes of LOC and ROC varied across restoration contexts. Among converted land‐use types, bareland‐derived restorations showed the largest relative increases in LOC and ROC but remained furthest from natural wetland levels, whereas paddy‐derived restorations exhibited the smallest gains yet were closest to natural levels. Across restored wetland types, peatlands showed greater ROC accumulation but more limited LOC accumulation, whereas coastal wetlands showed greater LOC accumulation but more constrained ROC accumulation. Among restoration strategies, combined restoration produced the most sustained increases in both carbon pools over time compared with either planted or rewetted restoration alone. Synthesis and applications . These findings show that the slow recovery of the relatively stable SOC pool constrains long‐term soil carbon restoration in wetlands, underscoring the need to integrate ROC‐based metrics into the evaluation of long‐term carbon sequestration during restoration.