A Global Meta-Analysis of Land Use Change on Soil Mineral-Associated and Particulate Organic Carbon.

Separating soil organic carbon (SOC) into mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) enables accurate prediction of SOC vulnerability to land use change (LUC). Here, we synthesize the responses of soil MAOC and POC to LUC, including land restoration and degradation, from 693 soil observations globally. We observed a large increase in soil MAOC and POC after restoration and a greater decline after degradation, but the magnitude and proportion of these two carbon fractions (fMAOC and fPOC) varied with LUC. POC, in comparison with MAOC, responded more sensitively to LUC, suggesting that POC was more vulnerable to environmental change. Using observed duration relationships, we found that the fraction of POC (fPOC) was higher at the early stage of restoration but lower at the late stage, projecting that soil carbon stability declined after short-term restoration but gradually increased after long-term restoration. Further analysis showed the context-dependent effects of LUC on carbon fractions: in arid or carbon-poor topsoil, restoration greatly increased soil carbon fractions and fPOC, while in humid or carbon-rich topsoil, degradation resulted in large decreases in POC and MAOC, especially POC. Overall, we highlight the importance of soil fractions, particularly POC, in predicting soil carbon stability and suggest that incorporating climate and initial carbon status in models of soil carbon dynamics helps to accurately predict future carbon sink potential.