Spatial distribution of soil organic carbon in the ecologically fragile Horqin Grassland of northeastern China

The spatial distribution of soil organic carbon (SOC) and its storage in the topmost 100 cm of the soil were investigated in the Horqin Grassland of northeastern China. Soil samples were collected at 1465 sites, covering 12.03 x 10(4) km(2). The region had a mean SOC density of 6.84 kg C m(-3), which is lower than China's mean (9.60 kg C m(-3)) and the world's mean (10.40 kg C m(-3)). The mean SOC density was much higher in the northern part of the study area (8.85 kg C m(-3)) than in the southern part (4.84 kg C m(-3)). The total SOC storage in the Horqin Grassland was 862.74 Tg. SOC storage decreased with increasing soil sampling depth. The SOC stored in the top 10, 20, 40, and 60 cm accounted for 17.7, 31.7, 53.8, and 71.3%, respectively, of the total amount in the top 100 cm. The region's extensive desertification appears to be one of the most important factors that led to the relatively low SOC content and the difference between the northern and southern parts of the Horqin Grassland. Our results provide an important baseline for evaluating past losses of SOC due to desertification, and for projecting the potential increase in SOC from the restoration of desertified land and how SOC will respond to climate change.