Variation of Soil Organic Carbon Stock under Land Use and Land Cover Changes in Farming-Pastoral Ecotone over the Past Century in Zhenlai, China

The impact of land use and land cover changes (LUCC) on global carbon cycle raises more and more serious concerns. Various methods were assessed to determine the influence of LUCC on soil organic carbon (SOC). However, the regional patterns and causes of terrestrial carbon sources and sinks remain uncertain. We analyze the variation of SOC stock in farming-pastoral ecotone in relation to LUCC over the past century in Zhenlai County located in the middle of northeast China. This study analyzes the characteristics of LUCC in Zhenlai County during the past century based on extensive historical literatures and remote sensing data. Based on abundant soil profile data, the SOC densities (0-30cm) in different land use and land cover types (LUCT) was analyzed. Then the change of SOC stock in the surface layer (0-30cm) caused by LUCC in this period was estimated with bookkeeping model, and we have also considered the impact of fertilizer management change. According to our results, during the past century, there was a rapid increase of cropland area from nearly zero to about 45% in the whole region, while the grassland area decreased from 68% in 1896 to 21% in 2004. Zhenlai region is a net source of CO² to the atmosphere owing to LUCC and fertilizer managements, which caused SOC stock decreased about 48% in the past century, especially during 1980-present.