The Relationships Between Biodiversity And Productivity Of Grassland And Xerophytic Shrub Ecosystems On The Mongolian Plateau

The relationships between biodiversity and ecosystem functioning(BEF)have been critical topics in ecological research during recent decades.Community productivity,as an important component of ecosystem functioning,is fundamentally vital for nearly all ecosystem goods and services.Although the relationships between biodiversity and productivity have been extensively studied,there remain an ongoing debate about the magnitude and directions of their relationships.Especially in natural ecosystems,biodiversity,productivity and their relationships are comprehensively affected by environmental factors(climate,soil,etc),community composition and research scale,thus show a more complex and uncertain relationship.Mongolian Plateau located in an arid and semi-arid area,is sensitive to global climate change,with obvious environmental gradients,multiple vegetation types,and diverse species composition.Therefore,it is an ideal place to study the BEF in the natural ecosystem.Studying the influence of environmental factors on the BEF relationships in natural ecosystems is of great significance for understanding ecosystem stability maintenance mechanism and responses of natural vegetation to global climate change and could provide useful information for the conservation,utilization and management of natural ecosystems.In the present study,the data of plant community,climate and soil properties were used to analyze the effects and mechanisms of environmental factors on the biodiversity,community biomass and their relationships in grassland and xerophytic shrub ecosystems on the Mongolian Plateau.The Random Forest model was used to screen the most important environmental factors affecting the biodiversity and community biomass,and then the Structural Equation Model was fitted to analyze the impact of environmental factors on biodiversity,community biomass and their relationships.Herbaceous plants in the grassland communities are divided into different plant functional groups,and the role and mechanism of community composition in regulating the influence of environmental factors on biodiversity and community biomass are explored.The main conclusions are as follows:1)Climatic factors are the most important environmental factor affecting the community biomass of the Mongolian plateau grassland and xerophytic shrub ecosystems,but the main indicators differ between ecosystems.Aridity index(i.e.,the coupling of precipitation and temperature in a large-scale spatial range)and the mean temperature in the coldest quarter are the most important climatic factors affecting the biomass of grassland and shrub communities,respectively.The soil factors that significantly affect the biomass of grasslands and shrub communities in the Mongolian plateau are different.The biomass of grassland communities is mainly affected by soil nutrients such as soil total nitrogen and total carbon;while the biomass of shrubs is mainly related to soil pH and soil structure(i.e.,soil gravel content).2)Climatic factors(mean annual temperature and mean annual precipitation)are the main factors affecting the species richness of grassland communities,followed by soil physical and chemical properties,such as soil pH,sand and silt content.The species richness of the shrub community is mainly affected by the shrub density,followed by the soil total carbon.However,the impact of climatic factors on the species richness of shrub communities is relatively less important than in the grassland community.3)The species diversity of the community is not the main factor affecting biomass of grasslands and xerophytic shrubs.Climate aridity or humidity was the most important factor mediating the relationship between species richness and community biomass.The effect of soil properties on the relationship between grassland species richness and community biomass is an indirect effect.In the shrub ecosystem,the mean temperature in the coldest quarter and soil pH directly determine shrub biomass,which in turn affects the relationship between biomass and species richness.4)In the grassland communities,the effects of climate and soil factors on the community biomass and species richness are mediated by the community composition or plant functional groups.Grasses play a key role in maintaining the biomass of grassland communities in the Mongolian Plateau.Climatic factors mainly regulate the community biomass by directly affecting the aboveground biomass of grasses.Alternatively,the species richness of plant functional groups,especially that of forbs,determines the species richness of the community and is indirectly affected by soil factors.The “mass ratio” effect and niche complementarity simultaneously affect the biomass and species richness of the Mongolian Plateau grassland community.The results indicate that climate is the major factor regulating the BEF relationship in arid and semi-arid natural ecosystems.Compared with climate factors,biodiversity is not a determinant of community biomass.Plant functional groups play an important role in regulating the effect of environmental factors on community biomass and biodiversity.Climate factors affect grassland community biomass by affecting biomass of grasses.The species richness of forbs determined plant species richness in the community and was indirectly affected by soil factors.This study expands the BEF theory in natural ecosystems at large-scale lever and provides a theoretical basis for natural grassland management.