Net primary productivity orchestrates uncertainty sources driving global soil organic carbon under land use change

Land use and cover changes (LULCC) have profoundly influenced global soil organic carbon (SOC) stock, yet SOC responses to LULCC are among the largest but least quantified uncertainties in estimating land carbon emissions. Here we comprehensively estimated the LULCC-induced SOC changes over the past century using data from three widely recognized model inter-comparison projects. A refined multi-dimensional diagnostic framework was employed to dissect the underlying processes governing SOC changes following LULCC. Results revealed notable discrepancies among models. Despite varying magnitudes, soil carbon residence time consistently contributed negatively to LULCC-induced SOC changes. Conversely, net primary productivity (NPP)-driven SOC changes emerged as the largest source of uncertainty, predominantly fueling SOC gains in some model ensembles but depletion in others. Our findings underscore the need to better constrain simulated NPP and soil turnover processes to improve the accuracy of LULCC-induced SOC change predictions, pivotal for advancing global carbon management and climate mitigation strategies. Soil carbon residence time contributed negatively to soil organic carbon changes induced by land use and land cover changes, with net primary productivity driven changes being the largest source of uncertainty, according to an estimation of soil organic carbon over the past century.