Spatiotemporal variability in divergent accrual of particulate and mineral-associated organic carbon by vegetation restoration on the Loess Plateau

Vegetation restoration is a promising climate mitigation strategy, with considerable potential for enhancing soil organic carbon (SOC) sequestration. However, knowledge on the effects of vegetation restoration on different SOC fractions remains poorly characterized. We conducted a regional synthesis to quantify how vegetation restoration, the most typical and successful agricultural land-use change on the Loess Plateau, affects particulate (POC) and mineral-associated organic carbon (MAOC). We found that vegetation restoration significantly increased SOC by 66 %, higher than the global average estimate (<45 %), with a much greater increase in POC (103 %) than in MAOC (48 %), which resulted in an increased proportion of POC in SOC but decreased that of MAOC. Moreover, the accrual of POC and MAOC was greater for conversion to forest and shrubland than to grassland, and for artificial restoration than for natural restoration, and for legume species than for non-legume species, respectively. Notably, the accrual of POC and MAOC showed divergent spatial and temporal dependencies. Spatially, the response of MAOC increased significantly, whereas that of POC showed no significant change with the latitude. With increasing soil depth, the response of POC and MAOC gradually decreased, but was always positive across the whole 0–400 cm profile. Temporally, the response of POC and MAOC increased significantly with time since restoration, and the increase in POC was more pronounced than that in MAOC and the accrual occurred approximately 2.5 years post-restoration. Collectively, our findings show a stronger accrual of POC relative to MAOC after vegetation restoration, along with their spatial and temporal dependencies, which underscore the importance of multi-pool management of SOC for accurately predicting the soil C sink potential in restored ecosystems.