The Effects Of Grazing On Soil Nutrient And Soil Microbes In Rhizosphere Of Stipa Grandis In The Typical Steppe

Grassland ecosystem was an open system, which was composed by abiotic factors (i.e. atmosphere and ground), biotic factors (i.e. animals, plants and microorganism) and productive labor factors (i.e. human economic activities). As a main utilization type of grassland, grazing was influence all aspects of grassland ecosystem, including above- and belowground. In below-ground ecosystem, rhizosphere was a relatively sensitive zone, which was an important interface of plant, soil, microorganism and their interaction. Storage capacity of soil nutrient and driving effect of soil microbes in rhizosphere were two key factors that determine input and output of substance. Therefore, depth understanding for the effect of grazing on soil nutrient and soil microbes in rhizosphere will provide new breakthrough point for study of grassland ecosystem.As the dominant species of the Inner Mongolia typical steppe, Stipa grandis was selected in our study. We studied the effect of grazing on plant biomass, plant nutrient, soil nutrient and microbes in rhizosphere and bulk soil. The effect of grazing on grassland ecosystem was described from the perspective of hizosphere, especially the interaction of abiotic factors and biotic factors in the below-ground, which would provide more credible evidence could be offered for scientific management of grassland. The main results were as follows:(1) In community level, as the beneficiary from the redistributed resource, Stip grandis had high grazing tolerance, which played an important regulating effect on community biomass.(2) The structural substance (i.e. C) in organ of Stipa grandis was not easy to be disturbed by grazing, whereas functional substance and storage substance (i.e. N and P) had changes of different degree. The N content of leaf and stem were raised as grazing densities increased, but N content of root decreased in all grazing treatments. P of stem and leaf were not sensitive to grazing, and P of root was first increased and then decreased. The N:P ratio of stem, leaf and root were less than 14, and N limitation expressed in plant community. The N content of root had closed correlations to N and NO3-N in rhizosphere soil.(3) Rhizosphere sequestration effect was weak in grazing disturbance, and grazing was decreased the OC (organic corban). N and AN in rhizosphere soil. Rhizosphere effect of soil P was not intensely, because it was hardly to transfer from soil to root. AP distributed spatial heterogeneity. Although it was changed in CK and grazing, the difference was not significant. The decline of soil N and AN led to N decreased in root. There was a significant correlation between soil nutrient and soil microbe, and soil nutrient could be more closely aligned with bacteria and fungi. There was a positive correlation between AN and soil microbe number.(4) The influence of over-grazing on culturable bacteria is mainly reflect in number decreasing, while the influence on culturable fungi is present number and species both reducing. OG (over-grazing) reduced the number of culturable bacteria and fungi greatly. In CK treatment, number of culturable bacteria in rhizosphere soil was highly more than bulk soil, and there was an obviously rhizosphere effect in rhizosphere soil. As the number reduced by over-grazing, rhizosphere effect of culturable bacteria was weakened in OG treatment. The number of culturable fungi was no different between CK and OG, that because fungal hyphae obscure the distinction between rhizosphere and bulk. Over-grazing also influenced the group composition of soil microbes. The number of Kocuria, Pseudomonas and Rhizobium decreased was the main reason leaded to culturable bacteria decreased in rhizosphere soil. Culturable fungi thus as Penicillium, Fusarium, Acremonium, Arthopyreniaceae, Alternaria, Absidia, Gibberella and Monographella was significantly reduced or became extinct by over-grazing in OG treatment. The reduction of these microbes could inhibit decomposition, and had a closed correlation with the decreasing of AN.(5) The high-throughput sequencing results showed that species number of soil microbes in phylum in bulk soil was more than rhizosphere. Species number (rhizosphere and bulk soil), richness and evenness (bulk soil) of soil microbes were reduced with grazing densities. Light grazing was benefit for microbe community maintaining, while microbe community would be changed under heavy grazing treatment。 In rhizosphere, the composition of microbe community was more easy to be influenced by C, N and P, and Verrucomicrobia and Planctomycetes had the significantly correlations to soil C. In bulk soil, the composition of microbe community was more easy to be influenced by P, N and AN, and Nitrospirae had a significantly correlation to soil N. Microbe community in rhizosphere was more sensitive to the change of environment factors, and its specific composition changed and number reduced would lead to soil nutrient decreasd.