Desertification effects on C and N content of sandy soils under grassland in Horqin, northern China

A field experiment was conducted in the Horqin sandy grassland, where desertification intensity gradients could be utilized to evaluate C and N concentration and storage in plants, litter and soil relative to the degree of desertification. The results showed that (1) grassland desertification could result in significant decreases in soil carbon and nitrogen storage, but the decrease of carbon and nitrogen concentration in plants and litter was not significant in the desertification processes; (2) carbon and nitrogen storage decreased significantly with increasing grassland desertification intensity; (3) carbon and nitrogen losses through desertification reached up to 107.53 Mt and 9.97 Mt in the Horqin Sand Land study plots during the last century, or 3.6 kg/m2 and 0.3 kg/m2; (4) 94.5% of carbon losses came from soil organic C, and 97.1% of the nitrogen lost by desertification came from soil total N; the carbon and nitrogen lost from plants and litter accounted for only 5.5% and 2.2% of total lost carbon and nitrogen, respectively; (5) most of the carbon and nitrogen are lost from the grassland in the early stages of the desertification process (in the light and moderate desertification stages), while C and N loss was less in later desertification stages; (6) the loss of soil organic C and N storage results mainly from the decrease of nutrient-rich soil fine particles eroded by wind. The decrease in plant and litter carbon and nitrogen storage results mainly from loss of soil potential productivity. Efforts to combat desertification in the Horqin Sand land should focus on preventing overgrazing and controlling soil erosion by wind in the critical early stages of the process.