The effect of land degradation and restoration on particulate and mineral-associated organic carbon

Land degradation and restoration profoundly affect soil organic carbon (SOC) dynamics. However, SOC consists of multiple pools with distinct properties, the comprehensive understanding about the responses of different SOC pools, such as particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) to land degradation and restoration are still lacking. Acquiring such knowledge is vital for optimizing mitigation strategies. In this study, we conducted a global meta-analysis on the effects of land degradation and restoration on POC and MAOC levels and their ratios to SOC by analyzing 1150 observations from 266 studies. Analysis showed that land degradation led to significant reductions in POC, MAOC and SOC by 47.1 %, 29.3 % and 34.1 %, respectively; POC was most affected. In contrast, land restoration increased POC, MAOC and SOC by 120.8 %, 49.1 % and 72.2 %, respectively; again, POC was the most affected. Land degradation reduced the POC/SOC and POC/MAOC ratios by 18.8 % and 21.0 %, while land restoration increased these rations by 38.5 % and 67.7 %. In addition, the MAOC/SOC ratio remained unchanged in response to land degradation but was reduced by 19.7 % under restoration. The responses of POC and MAOC to land degradation were primarily driven by the response of total nitrogen and silt. For land restoration, the response of POC and MAOC was mainly regulated by microbial biomass carbon (MBC). Our quantitative synthesis demonstrated that changes in land use exert significant effects on soil carbon dynamics and stability, thus highlighting the importance of managing these carbon pools. Quantifying POC and MAOC responses can provide a basis for optimizing the planning of land use so that we can manage soils as carbon sinks.