Grazing Management Regulates Grassland Ecosystem Functions And Services By Altering Plant Functional Traits In A Typical Steppe Of Inner Mongolia

The natural grassland in Inner Mongolia is the largest grassland in China,and provides multiple ecosystem services,such as animal production,carbon sequestration,erosion prevention,local climate regulation and nutrient cycling.Grazing is the most important land use in the grassland region,supporting the livelihood of the local community by through livestock production.It is of great significance to understand the dynamic mechanisms of grazing grassland ecosystems for developing ecologically sustainable grassland management systems,and especially the mechanisms of grassland ecosystems that response to different grazing regimes.Plant functional traits are sensitive to grazing disturbance,and have been considered as an important tool for analyzing the response and adaptation mechanisms of grassland plants to grazing.The links between plant functional traits and ecosystem functions and processes has been studied to understand the mechanisms of grazing management affecting ecosystem services and to select the proper functional traits for predicting the variation of ecosystem services under grazing management.In the present study,we studied the effects of grazing management on grassland ecosystem functions and services from an angle of grazing affecting plant functional traits(PFT).The grazing experiment was conducted in a typical steppe in central Inner Mongolia,and includes three related experiments to examine the effects of grazing intensity(nil,light,moderate,heavy grazing),livestock species(nil,sheep,cattle,goat at moderate grazing intensity)and grazing season(nil,spring,summer,autumn,and winter grazing).The response and adaptation of PFT of dominant species Leymus chinensis,Stipa grandis and Cleistogenes squarrosa across different grazing management were analyzed,along with the changes in plant community traits,and ecosystem functions and services.The major results are as follows:(1)Plant functional traits of three dominant species in the typical steppe of Inner Mongolia are jointly affected by grazing and precipitation variation.Leaf length,leaf area,stem length,and plant height all show an increasing trend with precipitation.And an increase in precipitation will widen the differences in plant PFTs among different grazing treatments.Light grazing promoted the leaf length,leaf area,stem length,plant height,and dry matter per plant.Sheep grazing at heavy intensity,and sheep,cattle and goat grazing at moderate grazing intensity all significantly decrease the plant height,leaf area,and stem length of L.chinensis and S.grandis.The leaf length,leaf area,stem length,and dry matter per plant of L.chinensis and S.grandis are mainly negatively affected by summer and autumn grazing,while the stem and leaf function of C.squarrosa is mainly negatively affected by winter grazing.(2)Plant community traits,such as height,clump size,leaf length,and leaf area decrease with the increasing grazing intensity,resulting in the changes in aboveground ecosystem processes and functions like community biomass and stoichiometric characteristics,and ultimately affecting the supply of the provisioning and regulating services of grassland ecosystems.Grassland under light grazing supplies the highest regulating and total services;grassland under moderate grazing supplies the highest provisioning services and supporting services;and grassland under heavy grazing provides the lowest regulating and total ecosystem services.This results indicate that moderate grazing and light grazing are better management measures for achieving the highest products provision and sustainable development of grassland ecosystem,respectively.(3)Cattle and goat grazing decrease sensitive traits of plants,such as dry matter per plant,clump size,plant height and leaf length,which lead to an increase in forage supply but a decrease in community aboveground biomass and regulating services in grassland.Therefore,cattle grazing seems the best for achieving an improved economic benefits while reducing ecosystem damages,compared to sheep and goat grazing under the same grazing intensity.(4)Plant community height and aboveground biomass of the grassland subject to spring or winter grazing are higher than those subject to summer,autumn grazing or nil grazing.This difference is mainly a consequence of the seasonal variation patterns in plant litter cover across the seasonal grazing.A higher litter mass or cover benefits to soil moisture by trapping snow in winter and reducing soil evaporation during the growing season,which is beneficial to plant growth;Removal of litter before the growing season increases solar radiation reception,which also improves soil temperature and plant production.Thus,grazing in spring or winter is more effective than complete grazing exclusion in the natural restoration of degraded grasslands in Inner Mongolia.(5)The impact of seasonal grazing on the structure and function of grassland ecosystem is realized through its regulation of the litter mass that affects soil temperature and moisture in the regreening period of grassland,and plant community species composition and ecosystem functions in the peak growth period.The variation in plant community traits is an important intermediate process in which litter affects other ecosystem properties.Spring grazing improves plant community production function;summer grazing improves plant community light competition capacity but decreases their production function;winter grazing only reduces plant community support function;and autumn grazing decreases all the three functions.These changes are directly or indirectly affected by plant litter mass in the regreening period.The changes in plant community traits are important intermediate processes of seasonal grazing altering ecosystems structure and function.The improvement of plant community production function is beneficial to the increase of aboveground biomass and coverage,but not conducive to the accumulation process of belowground biomass and soil carbon and nitrogen storage.In summary,the response of plant species and communities as well as ecosystem properties to grazing regimes varies,and the variation in plant functional traits are proved to important in mediating the effects of grazing on ecosystem structure.The variation of plant functional traits may indicate the changes in ecosystem functions and services.This study has deepened the understanding of the mechanisms of various grazing management systems on ecosystem processes and services,and the understanding lays a foundation for optimizing the grazing management for achieving best outcomes of multiple ecosystem services.