Changes in surface soil organic carbon in semiarid degraded Horqin Grassland of northeastern China between the 1980s and the 2010s

Soil organic carbon (SOC) plays an important role in the global carbon cycle and in mitigating climate change. The Horqin Grassland is one of the largest grasslands in China and has undergone serious aeolian desertification in recent decades. We conducted the largest field inventory to date, with the highest density of soil sampling, and explored changes in SOC in the region over the 30-year gap between the 1980s and the 2010s. Our results indicated that the mean SOC density to a depth of 20 cm decreased from 2.58 to 2.21 kg C m(-2), while the total SOC storage decreased from 311.11 to 266.70 Tg C, at an average of 12.29 g C m(-2) yr(-1). We ranked the SOC densities by ecosystem as woodland > grassland > cropland > sandy land. The decreased SOC storage in the Horqin Grassland can be ascribed to a combination of increasing temperature, decreasing precipitation, an expansion of the areas of extremely severely desertified land and cropland, and shrinkage of the grassland area. Our results provide an important updated regional baseline for quantifying how SOC storage will respond to future climate change and anthropogenic activities. Our results will also help policy makers determine how to achieve sustainable development of agriculture, forestry, and animal husbandry based on carbon sequestration.