Mechanisms And Interaction Effects Of Shortterm Nitrogen And Phosphorus Fertilization And Cold-season Grazing On Plant Diversity And Productivity Of Alpine Meadow

Nutrients and herbivores often simultaneously affect and jointly control grassland communities structure and function.However,most previous fertilization experiments have been conducted in fences,and few studies have been conducted on the interactions of fertilization and grazing on grassland.In this study,we set up fenced and grazing plots in alpine meadows in Henan County,the Tibetan Plateau,and conducted two consecutive years of nitrogen and phosphorus addition experiments to investigate the interaction and mechanisms of short-term fertilization and fenced or grazing on plant diversity and productivity in alpine meadows,so as to provide an ecological theoretical basis and reference for vegetation restoration in degraded alpine meadows.The main research results are as follows:1.Nitrogen and phosphorus addition alone and in combination had no significant effects on cover,leaf dry weight,specific leaf area and relative growth rate of the dominant species Elymus nutans,Koeleria litvinowii,and Potentilla anserina.Coldseason grazing significantly reduced the height of the dominant plant species and the coverage of the main dominant species of Elymus nutans,but significantly increased the coverage of Potentilla anserina.Cold-season grazing also significantly reduced the leaf area,leaf dry weight,specific leaf area of Elymus nutans and the leaf area of Koeleria litvinowii.2.Nitrogen application significantly increased total aboveground biomass and grass biomass of the plant community in both fenced and grazed sites,while phosphorus and the interaction between nitrogen and phosphorus did not significantly affect total aboveground biomass and grass biomass of the community,which is a good evidence that plant growth in this region is limited by nitrogen.3.Nitrogen addition significantly reduced the light transmittance of plant community.Grazing significantly increased the light transmittance of plant community,which suggested that fertilization and grazing play a balance force in regulating light transmittance of plant community.4.The aboveground biomass and grass biomass were positively correlated with soil available nitrogen.Species richness is negatively correlated with the aboveground biomass and grass biomass,but positively correlated with community light transmittance.Grazing reduces the aboveground biomass and the aboveground biomass of grass through feeding and other ways,thereby increasing the light transmittance of plant community,decreasing light competition,promoting species coexistence.Fertilization increases the aboveground biomass and the aboveground biomass of grass via increasing soil available nitrogen,thereby reducing the light transmittance of plant community,and then led to species loss.The structural equation model showed that the effects of cold-season grazing and nitrogen and phosphorus fertilization on species richness are mainly driven by changing light competition and plant productivity.Therefore,grazing is beneficial to alleviate the impact of nitrogen deposition and maintain the stability of plant diversity in the community.