Influence of Initial Soil Organic Carbon in Grassland on the Sensitivity of Carbon Changes to Climate After Grassland-to-Cropland Conversion

The conversion of grassland to cropland alters the terrestrial carbon cycle. However, changes in soil organic carbon (SOC) induced by grassland reclamation are poorly quantified due to the scarcity of large-scale-sampling data. Through paired sampling of 101 cropland and 101 grassland plots, this study examined changes in SOC resulting from conversion of grassland to cropland in an agropastoral ecotone of northern China. Results showed that grassland reclamation caused an average decrease of 16.07% in the surface (0–10 cm) SOC content. Over 80% of this region experienced SOC loss, while less than 20% showed increased SOC. As grassland soil organic carbon increased, the sensitivity of soil organic carbon changes to climate change following grassland-to-cropland conversion decreased, while the positive effects of changes in water flux and the normalized difference vegetation index (NDVI) strengthened. The most important factor influencing the change in SOC after grassland reclamation was the change in NDVI in low and medium SOC grasslands and the change in vegetation transpiration in high-SOC grasslands. This study found spatial heterogeneity in the effects of grassland reclamation on SOC at the regional scale and offers insights into enhancing regional SOC sequestration.