Effects Of Grazing On Biodiversity And Ecosystem Functions Of Stipa Breviflora Desert Steppe

Biodiversity is closely related to human production and life by driving the ecosystem functions.In recent years,the biodiversity of many ecosystems drastically declines with the frequent disturbance of human activities,which threatens the survival environment of mankind.As the most widespread utilization of grasslands,herbivore grazing is theprimary disturbance affecting grassland ecosystem functions.The desert steppe is an important type of semi-arid steppein Eurasia,as a transitional zone between typical steppe and desert.Additionally,the desert steppe provides significant resources forlivestock production in northern China.However,overgrazing is regarded as one of main causes of the desert steppe degradation and desertification over recent decades.Therefore,exploring the effects of sheep grazing on the biodiversity and ecosystem functions forprovidinga foresight intopreservation of biodiversityand sustainability of agriculture development in desert steppe.The studywas set up in a Stipa brevifloradesert steppein Inner Mongolia,northern China in 2004.A grazing experiment with a completelyrandomized block design having4treatments and 3 replicates.Here,we set four grazing intensity treatments:no grazing(control),lightgrazing(LG),moderate grazing(MG)and heavygrazing(HG)(the stocking rate was 0,0.91,1.82 and 2.71 sheep ha-1 half year,respectively)with sheep grazing over 12 years in the desert steppe.The objectivesof this study were to examine that the effects of grazing intensity on species composition,productivity and stability in plant community,plant diversity and soil microbial diversity,andexplore the relationship between plant diversity and soil microbial diversity as well as the relationship betweenbiodiversityand ecosystem functionsin grazing system,and to reveal the key regulatory role of plant diversity and microbial diversity in the process of grazing affecting ecosystem functions.The main conclusions are summarized as follows:1.Grazing hadthe significant negative effect on species diversity in plant community.Species richness,Margalefs index,Shannon-Wiener index and Pielou's index decreased significantly with increasing grazing intensity.In addition,grazing significantly reduced the relative density of subordinate species,such as perennial forbs,and increased the relative density of dominant species Stipa breviflora and Cleistogenes songorica.2.Grazing reduced the productivity of plant community.Above-and belowground net primary productivity decreased significantly,but the B/A ratioincreased significantly with increasing grazing intensity.Both above-and belowground net primary productivity hadthe positive linear relationships with species diversity,respectively.In addition,grazing disturbance had a greater indirect effect on aboveground productivity via plant diversity.3.Grazing reduced the stability of plant community.Temporal stability,resistance and resilience of plant community decreased significantly with increasing grazing intensity.In addition,heavy grazing decreased the species asynchrony of plant community.Furthermore,species diversity was a key indirect factor to the resilience of plant community,while species asynchrony was an important indirect factor to the temporal stability of plant community in response to grazing disturbance and climatic factors.Additionally,dominant species played a key role to maintain temporal stability under grazing disturbance,while subordinate species was a key to determinethe resistance and resilience in response to climatic factors.4.The soil physical and chemical properties(soil temperature,soil moisture,bulk density and pH value)as well as soil nutrients(soil organic matter,total nutrients,available nutrients)were not sensitive in response to grazing.However,the soil microbial diversity in the soil surface(0-5cm)decreased significantly with the increasing grazing intensity,and positively correlated with soil nutrients.In addition,the soil microbes were closely related to the soil physical and chemical properties.5.There werethe closelyrelationships between plants and microbes in the desert steppe.Soil microbial diversity hadthe positivecorrelations with plant diversity and community productivity.Plant diversity indirectly had a positive effect on soil microbial diversity by increasing the input of soil organic matter through regulating the biomass of dominant species and litters in the plant community.Meanwhile,soil microbial diversity hada significant effect on soil available nutrients by the interactions between actinomycetes and bacteria,and then indirectly affected plant diversity throughthe complementary effect of perennial bunch grasses and perennial forbs.Additionally,although grazing had significant indirect effects on the ecosystem functions by plant diversity and soil microbial diversity,plant diversity played a more significant role in regulating ecosystem functions.Our study demonstrates that continuousheavygrazing intensity can cause a continuous declinein plantdiversity andecosystem functions in the desert steppe.Additionally,there is a critical relationship between biodiversity and ecosystem functions in the Stipa brevifloradesert steppe,and plant diversity is a key indirect factor that determines ecosystem functions in response to grazing disturbance.Consequently,reducing grazing pressure should be an effective way to cnnservehindiversitv and the sustainable utilization of grassland inthe desert steppe.