Response Of Seasonal Regulation Of Grazing Intensity On Community Characteristics And Soil In Stipa Breviflora Desert Steppe

One of the majorest ways of using desert grassland is grazing. In recent years, since pastoral livestock amounts dramatically increased and the irrationally frequent activities of human beings acquired the material and energy from the grassland,the grass degenerated at an unprecedented rate and whilst the ecological environment suffered serious damage. Our research was based on Stipa breviflora desert grassland to investigate the effects of seasonal regulation of grazing intensity on each treatment area vegetation characteristics, physical and chemical properties of soil, and ecological stoichiometry. Here were our main conclusions from2010-2013four years of experiments:1Different species effects of seasonal regulation of grazing intensity were differentiation. Stipa breviflora, Allium polyrhizum density were tendency of decreasing and Cleistogenes songorica, Convolvulus ammannii density increased under heavy grazing condition. The density of Stipa breviflora and Allium polyrhizum under the condition(including zero-grazing in spring+severe grazing in summer+moderate grazing in autumn) was higher than the condition(including zero-grazing in spring+moderate grazing in summer+severe grazing in autumn). Plant species(Cleistogenes songorica, Convolvulus ammannii) coverage and density under full-year heavy grazing was higher than the zero-grazing in spring+severe grazing in summer+moderate grazing in autumn pattern, but Stipa breviflora, Allium polyrhizum’s were quite the contrary. Stipa breviflora aboveground standing crop under the whole year heavy grazing was lower than the zero-grazing in spring+severe grazing in summer+moderate grazing in autumn pattern, but Cleistogenes songorica’s was quite the contrary. Aboveground standing crop of Allium polyrhizum under heavy grazing was lower than other grazing treatments and the grazing treatment areas of Convolvulus ammannii aboveground standing crop generally speaking had the enhancement to the control treatment.2Stipa breviflora and Allium polyrhizum foliage branch and fertile stem amounts under zero-grazing in spring were larger than other treatments. Due to the adaptable adjustment, Stipa breviflora foliage branch and fertile stem amounts were low under the whole year heavy grazing. And it may increase the proportion of Allium polyrhizum fertile stem growing under zero-grazing in spring. 3Stipa breviflora, Cleistogenes songorica and Allium polyrhizum Levins niche breadth index were higher than other plants. The niche overlap index of Stipa breviflora and Allium polyrhizum were maximum under severe in spring+severe grazing in summer+severe grazing in autumn, however, Cleistogenes songorica and Allium polyrhizum’s were minimum under severe in spring+severe grazing in summer+severe grazing in autumn and Stipa breviflora,Cleistogenes songorica’s were lower under heavy grazing treatments.4Stipa breviflora distributed randomly on a smaller scale, which performed a cluster distribution with the increased of scales. Heavy grazing in whole grazing season made Stipa breviflora only cluster distribution on a large scale. Cleistogenes songorica had a cluster distribution on a larger scale in heavy grazing in spring+heavy grazing in summer+moderate grazing in autumn and heavy grazing in whole grazing season conditions. Allium polyrhizum distributed cluster on a larger scale in continuous heavy grazing condition, while there was no cluster distribution within the scale of250cm in other grazing treatments. Stipa breviflora and Cleistogenes songorica had the characteristics of sectors on a small scale, which was the opposite in Allium polyrhizum. Stipa breviflora and Allium polyrhizum had no correlation with in scale of250cm in treatment of heavy grazing in whole grazing season, but showed a positive association with the increased of scales in treatments of banning in spring+heavy grazing in summer+moderate grazing in autumn and banning in spring+moderate grazing in summer+heavy grazing in autumn.5The important value of Stipa breviflora decreased in treatment of banning in spring+heavy grazing in summer+moderate grazing in autumn, but which of Cleistogenes songorica was higher than that of banning in spring+moderate grazing in summer+heavy grazing in autumn, also which of Allium polyrhizum was lower than that, while Convolvulus ammannii was opposite. From the perspective of functional group, the important value of perennial forbs was the minimum in treatment of continuous heavy grazing, while which of biennial forbs was the maximum in the same treatment. Continuous heavy grazing in whole season significantly reduced the community productivity, but increased the community diversity. There was a highest variation coefficient on community aboveground standing crop in continuous heavy grazing treatment. The variation coefficients of aboveground standing crop in banning in spring+heavy grazing in summer+moderate grazing in autumn was lower than that in moderate grazing in spring, summer+heavy grazing in autumn. The variation coefficients of perennial forbs and grasses was small, the opposite showed in shrubs, bushes and biennial herbaceous.6The total nitrogen in continuous heavy grazing area had a trend of decreased, available nitrogen in continuous heavy grazing area was higher than that in banning in spring+heavy grazing in summer+moderate grazing in autumn and banning in spring+heavy grazing in summer, autumn. Moderate grazing could increase soil organic matter, but there was a decrease trend in continuous heavy grazing condition. Nutrient of internal grassland ecological system affected each other, organic matter significantly correlated with potassium and total nitrogen. Available phosphorus significantly associated with ammonium and nitrate, and there was a very significant correlation between ammonium and nitrate.7The main plant of N/P was lower14%in Stipa breviflora Desert Steppe. The main plant growth is limited by N. The seasonal variation of leaf C, N and P and C:N, C:P an d N:P mass ratios were also dramatically different. The coefficient of variation (CV) of Leaf leaf C, N and P contents and C:N, C:P and N:P mass ratio was P (36.88%)>C/P (33.97%)>N/P (27.85%)>N (23.81%)>C/N (21.58%)>C (6.17%)。The range of seasonal CV values for C and C/N was2.58%-14.09%,14.85%-29.92%, respectively, and P was26.39%-51.56%, N was18.39%-36.51%, C/N and C/P was14.85%-29.92%,26.29%-43.38%, respectively. The range of C:N ratios of soil was7.86%-11.60%, lower the mean of our country(10-12). The C:P ratios of soil was19.54%-38.22%, lower the mean105. The C:P ratios of soil was2.42%-4.43%, lower the mean of china(8).8The regulation of banning grazing in spring+heavy grazing in summer+moderate grazing in autumn was more reasonable in Stipa breviflora desert steppe.