Changes Of The Soil Microbe Under Different Intensities Of Grazing And Root Exudates On Leymus Chinensis Grassland Of The Songnen Plains

Grazing behavior of herbivore is one of the important management methods in the natural grasslands. The characteristics of vegetation or soil, even the recycle of nutrient matter of grasslands are influenced by animal behavior of grazing, trampling and excreting. Root exudates of plants also could be impacted by the grazing behavior, and then the microbe in the soil could be affected by root exudates. Studies on the relationships between grazing, physical and chemical characteristics of soil and the soil microbe could not only illustrate the ecological results of animal foraging, but also discover the mechanism of soil degradation, thereby provided theoretical evidence for the reasonable management of grassland ecosystem. Plant height, density and biomass of plant population were observed and measured in four plots with different intensity of grazing in the summer of 2003 on the Songnen Plains. In addition, the characteristics of soil including soil moisture, pH value and electrical conductivity and the number of microbes also were investigated. The responses of the characteristics of vegetation and soil, the number of microbes to the intensity of grazing, and the relationships between characteristics of vegetation or those of soil and the number of microbes was analyzed. There were few experiments on the microbes on the natural grasslands and the effects of grazing on the root exudates. In this experiment, root exudates of Leymus chinensis and the effects of grazing on the composition of root exudates was studied. Mean plant height and aboveground biomass declined with the increase of the intensity of grazing, and reverse for the density. Mean plant height and aboveground biomass was 47.71cm and 77g/m2 respectively in the control treatment. However, the mean plant height reduce sharply to 25.81, 15.71, 6.12cm with the increase of the intensity of grazing. And the aboveground biomass also declined sharply to 27, 17 and 4g/m2 along the grazing gradient. The important value of L. chinensis was 0.79 in the control treatment, and changed to 0.73, 0.60 and 0.54 with the rise of the intensity of grazing. There was no significant change for the characteristics of soil between layer 10-20cm and 20-30cm, which illustrated that the soil surface (0-10cm) was influences mostly by the grazing behavior. There were no significant correlations between the characteristics of soil and the intensity of grazing due to the rainfall and topography of the experiment plots. The number of microbes decreased with the rise of the intensity of grazing to some extent because plants were foraged by animals and soil was destroyed, which resulted in the decline of biomass and the organic matter of soil. The number of each kind of microbe ranked as control> light grazing >moderate grazing >heavy grazing. The number of each kind of microbe in each plot of different layers ranked as 0-10cm>10-20cm>20-30cm. In addition, the number of bacteria was usually larger than that of actinomycetes, and the number of actinomycetes was larger than fungi. There was significant regression relationship between the characteristics of vegetation and the number of microbes (P<0.05). There was a close correlation between the number of fungi and the characteristics of the vegetation, indicating that the characteristics of the vegetation could impact the number of fungi at most. Moreover, the experimental results showed that there was no significant correlation between the number of actinomycetes and the characteristics of the vegetation. There were more than twenty kinds of organic acid and sixteen kinds of amino acid detected in the experiment about root exudates. Most detected organic acid was recorded. Few that was unrecorded may be the ramification of the recorded or be the exudation of the resin. Thereby in order to make clear the function of the root exudates in the ecosystem of rhizosphere of L. chinensis, we must get every special pure extraction from the root exudates of L. chinensis. Further experiments were needed in optimizing the methods and conditions.