Effects Of Grazing Exclusion On Plant Community Composition And Carbon Storage Of Alpine Meadow In Qinghai-Tibet Plateau

Alpine meadow is one of the most important grassland types in the Qinghai-Tibet Plateau.Human activities,including grazing and grazing exclusion,have a profound impact on the composition,structure and function of alpine meadow ecosystem in this region.In order to understand the impact of grazing exclusion measure on the restoration of the degraded alpine grasslands,it is necessary to explore the changes of plant community characteristics and ecosystem carbon storage under different periods of enclosure.In this study,four grassland sites with different enclosure time(2,4,9,11 years)were selected.The community height,coverage,species composition and community heterogeneity were investigated in the five plots both inside and outside the enclosure of each site.We also investigated the carbon storages of vegetation biomass(above-and below-ground)and soil after community investigation in each plot.Furthermore,the grazing exclusion measures were divided into two levels: short-(2 and 4 years)and long-term(9 and 11 years)exclusion,to explore the response of alpine meadow community composition and ecosystem carbon storage to different grazing exclusion treatments.We found that:(1)There was no significant difference in plant diversity index between short-term grazing exclusion and control(grazing).Long-term grazing exclusion significantly reduced species richness,but increased Simpson dominance index and community heterogeneity;(2)The long-term grazing exclusion changed the composition and structure of plant community,and the number of common species(1% < relative coverage < 5%)decreased,which led to the decrease of species richness;(3)Structural equation model(SEM)indicated that the long-term grazing exclusion reduced the species richness and plant diversity,and further increased the spatial heterogeneity of the community;(4)The long-term grazing exclusion significantly reduced the carbon storage of aboveground vegetation,while the carbon storage of roots and plant had no significant difference between the short-term grazing exclusion and the long-term grazing exclusion;(5)The short-term grazing exclusion increased the bulk density of soil(0-10 cm)and decreased the organic carbon content of soil(10-20 cm).There was no significant difference between short-term and long-term grazing exclusion on soil organic carbon storage.The results showed that the long-term grazing exclusion led to significant changes in the composition and structure of alpine meadow plant community,and the carbon pool of alpine meadow ecosystem as the main ecological function was also affected to some extent.Long term grazing exclusion is not conducive to the restoration and maintenance of alpine meadow ecosystem diversity,but also has no significant role in promoting the accumulation of plant and soil carbon pool,and even has a restraining effect.