The Characteristics’ Of Soil Stable Carbon Isotope In Different Types Of Grassland In Northwest Of China

Grassland ecosystem is an important part of carbon cycle and sequestration of land ecosystem, by which the globle carbon cycle is also affected. There is a large area of grassland in northwest China, according to the distribution of different types of grassland, we started a study in Inner Mongolia, Xinjiang and Tibet on Stipa breviflora desertification grassland, Sub-alpine meadow steppe, Alpine meadow steppe and alpine grassland, where soil and plant samples were collected to test the basic physical and chemical properties, soil organic carbon(SOC) content and δ13C value, applied with carbon stable isotope technology.The δ13C value of dominant plant species, litters and the correlation between them were also analyzed, the results are as following:SOC of top soil ascented with the increase of elevation, which showed that vegetation, climate and the basic characters of soil affected the rate of decomposition and transformation of soil organic matter. SOC decreased dramatically with the depth of soil profile and the extents were as follwing:NMG-01:92.26%, XJ-01:77.9%, XJ-02:77.67%, XZ-01:61.58%. XZ-02:88.55%; however, this character was not as obvious as it in Ejina Banner, Inner Mongolia because of the special structure of the soil profiles, where was a sand layer in the profile every10cm, which indicated that vegetation was not the only factor affected the vertical distribution of soil, the climate and the characters of soil itself would also affected the decomposition of SOC.The δ13C value became negative with elevation, which was mainly influenced by the vegetation; the vertical distribution of δ13C value was decided by the vegetation and climate during the period of soil formation, the δ13C value was extremely positive in Ejina Banner, Inner Mongolia, which showed that the climate and environmental conditions were the desicive factors.It showed an obvious negative correlatioin between SOC and δ13C value among all sites, which indicated a low level of organic matter decomposition; the δ13C value of Ejina Banner was much more positive than which in other sites of our study, expect XJ-01, XZ-01and XZ-02, the changes in amplitude of δ13C value of soil profiles in all the other sites were higher than3‰, that meant the rate of decomposition of soil organic carbon were higher in desert steppe in northwest China, and the resourse of organic matter were the mixture of C3and C4plants, which also indicated that the cliamate and vegetation would have changed dramatically in desert steppe in northwest China, and the climate could have been hot and wet in Sziwang Banner, Inner Mongolia.