Soil Carbon Characteristic And Carbon Sequestration Potential In Different Grassland Types On The Western Slopes Of Helan Mountain, China

Soil carbon pool is the largest global ecosystem carbon stocks, including soil organic carbon (SOC) pool and inorganic carbon (SIC) pool, had an important role in the global carbon cycle. In this study, different grassland types at different altitudes along Helan mountain was conducted in Alxa, Inner Mongolia, China. The paper studied the distribution characteristics of grassland soil carbon at arid desert area, and relationships between soil carbon with environment factors of climate, vegetation and soil. It also analyzed changes of soil carbon under grassland potential succession along altitudinal gradient. At last, effects of exclosure and grazing on soil carbon, carbon sequestration rate and carbon sequestration potential was researched. The results showed that:(1) As the altitude increasing, the steppe desert evolved into steppe, herbaceous vegetation shifted from shrubs,soil organic carbon content and density increasing, grassland types expressed as:steppe> desert steppe> steppe desert;soil inorganic carbon and total carbon content and density with altitude increased increase gradually, but decreased at2100m, the performance of:1960m steppe> desert steppe> steppe desert. In various grass types, soil organic carbon content and density in the vertical distribution of soil profile with soil profile deeper reduced, soil inorganic carbon and total carbon content and density showed the opposite trend.(2) Soil organic carbon, total carbon were significant correlated with annual mean temperature, annual precipitation, vegetation cover, biomass, soil pH, soil bulk density, soil total nitrogen and total phosphqrus, available nitrogen; soil inorganic carbon was significant correlated with annual mean temperature, annual precipitation, soil bulk density, total nitrogen, total phosphorus and soil available phosphorus, but had no correlation with vegetation cover and biomass, available nitrogen. Integrated partial correlation and regression analysis showed that:soil bulk density was significant correlated with soil total carbon;TN was significant correlated with soil organic carbon; the factors affecting soil inorganic carbon varied greatly, annual rainfall and annual average temperature were the main factor, soil bulk density was significant correlated with soil inorganic carbon. Partial correlation analysis showed that the role of soil carbon content was greater than soil bulk density in soil carbon density.(3)Due to the special arid desert environment and human grazing in Alxa, there was a serious phenomenon of grassland degradation. Meanwhile, with global warming, vegetation expand up along altitudinal gradient. By analyzing soil carbon changes in its state of grassland potential degradation, then found that on various degradation processes, soil organic carbon significantly decreased; inorganic carbon and total carbon were mixed, and significantly reduced when grassland types changed. The results indicate the status of grassland degradation greatest impacted on soil organic carbon.(4) The enclosure had an important role in soil carbon sequestration. After fencing, vegetation and soil properties of steppe desert and steppe have been significantly restored, soil carbon content increased. The steppe desert soil organic carbon and inorganic carbon density were significantly improved in enclosure, while on the steppe soil organic carbon density had not significant changed, soil inorganic carbon density increased.(5) Soil carbon density in steppe (13760g.m-2) was significantly greater than soil carbon density in steppe desert (5752g.m-2). Soil carbon sequestration potential of steppe was also significantly greater than the steppe desert, but soil carbon sequestration rate of steppe was significantly less than the steppe desert, the size and differences of carbon sequestration rate in steppe and steppe desert were mainly affected by inorganic carbon sequestration rate.