| Grazing is the most impotant factor which effects the plant productive, plant diversity and the composition structure of community. The analysis based on the effect of grazing on the root system distribution and its relationship with the on above-ground vegetation and soil environment, could make the study of the function mechanism on root by grazing more clearly, and make a further detect of the effect of grazing on the ecological system mechanism. Stipa baicalensis grassland was selected as the research object to analyze the influence of different grazing intensities on the above-ground, under-ground biomass, the root system distribution and its nutrient content , the main results showed as below:1.Under different grazing intensities, the plant diversity and productive of the Stipa baicalensis grassland changed significantly. as the grazing strength rising, vegetation coverage degree, species numbers, plant diversity and above-ground biomass reduced significantly; under heavy grazing Grassland degradation occurred.2.The plant species of Stipa baicalensis grassland community were classified into functional groups based on differences in life form and ecological group. The ecological functions of Stipa baicalensis grassland mainly based on mesoxerophytes and xeromesophytes; the plant life form functional groups of Stipa baicalensis grassland mainly based on perennial herbaceous plants, including of perennial grasses, perennial bunchgrasses and perennial forbs, among five plant life form functional groups, perennial bunchgrasses based on hydrophobic plexus type grasses. The plant functional groups changed significantly under different grazing intensities: with grazing gradients adding, perennial bunchgrasses and perennial forbs reduced significantly, while perennial grasses first increased and then declined significantly, but shrubs or sub一shrubs and annuals increased significantly; mesoxerophytes and xeromesophytes was replaced by xerophytes.3.Roots of Stipa baicalensis grassland community mainly gathered in 0 - 40 cm soil layer, Among them the root biomass in 0 - 10cm soil layer accounted for 65.88% - 82.60% of the total biomass in 0 - 40 cm soil, and the root of diameter<1mm was the most of them. The effect of grazing disturbance on vegetation and soil significantly changed the root system distribution, and roots with different diameters changed significantly. The roots of diameter≥2mm in 0 - 10cm soil layer and the roots of diameter<1mm in 0 - 40cm soil layer were more sensitive to grazing disturbance: in 0 - 10cm soil layer, the roots biomass distribution of diameter≥2mm under the light, middle and heavy grazing was 135.50,93.42,33.07 g.m-2; with grazing gradients adding, the root biomass distribution of the roots of diameter<1mm changed significantly: middle grazing>heavy grazing>light grazing; but in 0 - 40cm soil layer, with grazing gradients adding, the root biomass distribution of the roots of diameter<1mm changed significantly: light grazing>middle grazing>heavy grazing.4.Under grazing conditions, the roots total nitrogen, total phosphorus, total organic carbon content with different diameters in different soil layer changed significantly: With the grazing intensity increasing, the roots total organic carbon with different diameters all gradually decreasing in 10 - 30cm soil layer; the roots total nitrogen and total phosphorus with different diameters both creased significantly in 0 - 10cm soil layer .5. It showed that root system distribution had a certain degree of relevance with soil bulk density, water content, total nitrogen content, total phosphorus content, total organic carbon content and cation exchange capacity under different grazing intensities. The study showed that the soil physicochemical properties were influenced by grazing which mainly changed the biomass distribution of vegetation root system in different diameters, meanwhile the root system distribution by different diameters also had certain feedback effect on the soil physicochemical properties.
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