Soil carbon stability regulate carbon dynamics following large-scale afforestation.

Large-scale afforestation is considered an effective measure to mitigate climate change. However, due to the differences in the properties of soil organic carbon (SOC), the dynamic response of SOC to large-scale afforestation remained unclear. Therefore, we conducted paired sampling (farmland and afforestation) in plantation areas across northern China to evaluate the relationship between SOC stability and SOC increments (ΔSOC) resulting from afforestation. Our findings indicated that SOC-unstable soil supported greater carbon increments through afforestation, but at the expense of reduced SOC stability after afforestation. Additionally, we observed that this relationship exhibited geographical characteristics, with SOC-unstable soil demonstrating a stronger capacity to enhance ΔSOC at higher latitudes, particularly in the topsoil. This is primarily attributed to the fact that higher latitudes and colder climates enhance the contribution of particulate organic carbon to ΔSOC and weaken the regulatory effect of SOC chemical composition (carboxyl and aromatic carbon) on SOC stability after afforestation. These findings underscore the importance of incorporating pre-afforestation SOC stability to accurately predict soil carbon-afforestation feedback.