Effects Of Grazing Exclusion On Vegetation And Soil Fractions Of Active Organic Carbon Of Seriphidium Transiliense Desert Under Moderate Degeneration

The effects of grazing exclusion(including 0 year, 1 year, 4 years and 11 years) on grassland population characteristics and community characteristics, biological diversity, soil nutrients and soil fractions of active organic carbon(readily oxidizable carbon, light fraction organic carbon and nitrogen, particulate organic carbon and nitrogen, microbial biomass carbon and nitrogen) of Seriphidium transiliense desert were studied. These indexs which reflect soil quality were screened by principal component analysis, and then inquiry the relationship of regression between plants, soil nutrients and grazing exclusion times, which provided a reliable scientific basis for the reconstruction and management of S. transiliense desert under moderate degeneration. Some conclusions can be drawn as follows:(1) The important values of S. transiliense appeared the fluctuation of “up-down-up” with the increasing of grazing exclusion years, however, Kochia prostrata, Festuca ovina, Carex turkestanica appeared the fluctuation of “down- up- down”; the population height, coverage, biomass of S. transiliense and community coverage, biomass were increased with the increasing of grazing exclusion years, but their density were increased first and then decreased. Simpson index, diversity index and evenness index of communities appeared first fall then increased and decreased along with grazing exclusion period increasing, species richness index showed a gradually decreasing trend.(2) The content of soil organic matter, total nitrogen, total phosphorus, available potassium substantially increased first and then decreased(“V” shape change) with the increasing of grazing exclusion times in the surface(0~5 cm). The soil moisture presented increased volatility, but soil bulk density presented decreased volatility. Compared with continuous grazing areas, the content of soil organic matter decreased 11.9%~23.0% in 0~5 cm of soil layer and total nitrogen decreased 31.3%~46.7% in 5~10 cm of soil layer; but the content of total phosphorus and available potassium respectively increased 8.5% and 12.0% in eleven years of grazing exclusion. In addition, the content of total potassium, alkali solution nitrogen, available phosphorus had no obvious change.(3) Compared with outside the fence, readily oxidizable carbon inside the fence in 0~50 cm soil layer increased by 54.1~111.8%, 144.7%~219.8%, 176.1~212.2%, 73.4~94.4%, 90.8~132.4%, respectively; and light fraction organic carbon and nitrogen in 5~10 cm respectively significantly increased by 42.9%~77.8%, 43.5%~86.4%. With the increasing of grazing exclusion times, the microbial biomass carbon in 0~50 cm soil layer, microbial biomass nitrogen and its distribution ratio in the soil surface(0~5 cm) appeared the fluctuation of “up – down- up”. From the range of change to see, readily oxidizable carbon of 0~20 cm soil layer, light fraction organic carbon and nitrogen of 5~10 cm soil layer, microbial biomass nitrogen could be used as sensitive indicators of soil organic carbon in S. transiliense desert under grazing exclusion.(4) Light fraction organic nitrogen, microbial biomass carbon, alkali solution nitrogen, particulate organic carbon and its distribution ratio, total phosphorus were selected as the index of minimum dataset by the way of principal component analysis. Regression analysis showed that grassland productivity and plants growth condition were optimal after grazing exclusion 7~11 a. However, soil quality recovered gradually in 8~10 a. Due to the studys were restricted by time gradient and node of grazing exclusion, we need to continue evaluate the best times of grazing exclusion by the way of increasing time node and shortening time gradient.