Response Of Seriphidium Transiliense Vegetation Characteristics To Grazing Disturance In Desert Grasslands

Sagebrush desert is not only the major component of spring-autumn or winter-spring pasture in Xinjiang,but also is the frontier of grassland degradation,which plays a vital role on the development of seasonal animal husbandry and the maintenance of fragile ecosystem.Seriphidium transiliense desert,mainly distributed in the Xinjiang area.But in recent years,it has become a serious disaster area of grassland degradation due to its overgrazing,climate change and other factors,which needs to be restored urgently.Exploring the response of individuals,population of S.transiliense and graassland communities to grazing has important guiding significance for understanding the degradation succession mechanism and evaluating the suitability of grassland resources carrying capacity.Given this situation,we conducted our field experiment in the Ashili Kazak nationality township of Changji city in Xinjiang from 2012 to 2014.In this study,phenotypic and population quantitative characteristics of S.transiliense,plant diversity and community quantitative characteristics under different grazing intensities(no-grazing,lightly grazing,moderately grazing and heavily grazing)were determined_in three consecutive years of monitoring,which aimed to clarify the general rules of interannual and monthly variations of the vegetation response to grazing in S.transiliense desert from three aspects of individual--population--community.Furthermore,the sensitive indexes of grazing response were screened and the relationship between the sensitive indexes was explored.Finally,the response strategies of S.transiliense population to grazing disturbance were attempted to clarify,and the grazing management theory was enriched and developed,which provided a scientific basis for understanding the degradation process of desert grassland and improving the system of desert ecological protection.The main results showed that:(1)Phenotypic characteristics(component characteristics)Grazing reduced the crown area,root neck length,root neck diameter and root length of S.transiliense,respectively.With the increase of grazing intensity,the response rate of crown area,root neck length and root neck diameter decreased gradually on the whole,and with the increase of years,the canopy area decreased under the same grazing intensity,and the cluster of S.transiliense showed a a tendency of miniaturization after grazing.In general,grazing basically promoted the increase of specific leaf area and the number of first-order branches of S.transiliense,and the response value of first-order branches in lightly and moderately grazing areas were significantly higher than that in no grazing heavy grazing areas.Under the same grazing treatment,the response rate of the numbers of first-order branches were the highest in July,and moderately grazing was beneficial to the growth of new branches.(2)Quantitative characteristics of populationThere were some differences in the response of population characteristics to the years and grazing intensities.Grazing reduced the height and biomass of S.transiliense population,and the response rate gradually decreased with the increase of grazing intensity.From the grazing intensity perspective,the effect of grazing on the density of S.transiliense population were different in different months,which had both positive and negative response,and mostly founds were negative responses.It also showed that the population density reached the lowest in the heavy grazing area.There was a certain correlation relationship between the height,density and biomass of S.transiliense population,which was related to the sampling year.(3)The quantitative characteristics and diversity of desert communityGrazing significantly reduced community biomass,and the biomass of different grazing intensity areas decreased gradually with the increase of growing season at the same year.The response rate of community density and coverage had differences in different grazing intensity and months,which had both positive and negative response,and the highest value appeared in lightly or moderately grazing area,and moderately grazing area could promote community density and coverage.The effects of grazing intensity on plant diversity were complex,and there were both positive effects(grazing increased plant diversity)and negative effects(grazing decreased plant diversity),which related to years and growing season stages.(4)Screening of sensitive indicatorsThe sensitive indicators to grazing were crown area(plasticity range 71.6%?74.5%),first-order branchs numbers(plasticity range 0.7%?48.4%),populating biomass(plasticity range 85.2%-96.4%)and community biomass(plasticity range 73.2%?2.9%),respectively.The specific leaf area,root length,root neck diameter and plasticity of root and neck length of S.transiliense were relatively small,which showed that the response of the underground parts to the grazing disturbance were rather slow.There was a significant negative correlation between the number of first-order branches and the crown area of S.transiliense under moderately and heavily grazing areas,and a significant positive correlation between the crown area and the population biomass of S.transiliense under heavily grazing area.In the non-grazing area,the population biomass of S.transiliense was positively correlated with the community biomass,but negatively correlated in the grazing areas,although the correlation was not significant.