Impacts of Land Conversion on Soil Organic Carbon and Nitrogen Stock: Magnitude and Uncertainties

Changes in soil organic carbon (SOC) and soil organic nitrogen (SON) would alter the global carbon and nitrogen cycles through influencing the composition, structure, and functioning of ecosystems. Land use and land cover change (LULCC) is the most important anthropogenic factor that affects the SOC and SON storage. A wide variety of efforts have been conducted to quantify the effects of LULCC on global SOC and SON stock in the past decades. However, highly uncertainties still exist in these estimates. It remains unclear to what extent the historical land conversion has affected the SOC and SON. The objective of this study is to provide a robust estimate of SOC and SON changes resulting from the long-term land conversion among forests, grasslands, and croplands. We used a process-based ecosystem model (Dynamic Land Ecosystem Model, DLEM) in conjunction with geo-referenced data sets and soil inventory data to quantify spatiotemporal dynamics of global SOC and SON over a century scale. Driven by multiple sources of land use and land cover data sets including MODIS, ESA CCI, HYDE3.2, LUH2, VCF5KR, ISAM-RF, and ISAM-HH, the DLEM examines uncertainties induced by different data sets. Simulated results show large divergence in SOC and SON changes induced by land conversion among forests, grasslands, and croplands due to the different land classification schemes of land cover data sets. The outcomes of this research may provide insights for policymakers and land managers into initiating adaptive strategies to mitigate the negative effects of global warming in the future.