Distribution of soil carbon and its losing risk with potential degradation on the grasslands along western slope of Helan mountain, China

In order to study the distribution and changes of soil organic carbon (SOC) and inorganic carbon (SIC) and total carbon with grassland potential degradation following altitudes along Helan Mountain, meanwhile explore their relationships with environment factors of climate, vegetation and soil, we collected soil samples and plant samples in three grassland types at different altitudes along Helan mountain in Alxa, Inner Mongolia, China. The different soil indexs which mainly included soil pH, Soil organic carbon, total carbon, soil total nitrogen (TN), total phosphorus, available nitrogen and soil bulk density were measured. The relationships between soil carbon with environment factors of climate, vegetation and soil were analyzed by integrated partial correlation analysis. The results showed, as the altitude increasing, soil organic carbon content and density increase and were expressed as grassland types: steppe> desert steppe> steppe desert. However, soil inorganic carbon and total carbon content and density increase gradually with altitude increasing, but it slightly decreased at the grassland at altitude of 2 100 m. Integrated partial correlation analysis showed TN was significantly correlated with soil organic carbon. While, the factors affecting soil inorganic carbon varied greatly. Soil bulk density was significant correlated with soil inorganic carbon and annual rainfall and annual average temperature were the main factors too. Because soil carbon density was influenced greater by soil carbon content than soil bulk density, similar to soil carbon content, soil carbon density in steppe was significantly greater than soil carbon density in steppe desert. Additionally, if the grassland at the higher altitude changes to the situation as the lower altitude, soil organic carbon content and density decreased, but soil organic and total carbon content and density decreased only when the grassland types changed. The whole research revealed that the degradation of the grassland influenced both soil organic and inorganic carbon content and density, and the soil development influenced the soil organic carbon characteristics too.