Effects Of Tibetan Sheep And Yak Grazing On The Partitioning Of Soil-Grass Systems In Cool Season Pastures Of Alpine Meadows

The alpine meadow on the Qinghai Tibet Plateau is not only an important ecological barrier in China,but also a means of production for local herdsmen to survive.Grazing is the main utilization mode of alpine meadow in Qinghai Tibet Plateau.Yak and Tibetan sheep are the main livestock for grazing in alpine meadow.Long term grazing has a great impact on grassland vegetation and soil.The study on the impact of long-term grazing of different livestock on alpine meadow ecosystem from the perspective of soil microorganism and vegetation can provide a theoretical basis for the healthy and sustainable grazing management of alpine meadow.A large number of scholars have studied the impact of grazing on alpine meadow,but these studies mainly focus on the perspective of grazing intensity,vegetation community structure and soil properties,and lack of systematic research on"vegetation-soil-microorganism"system.Moreover,most studies focus on single grazing livestock,and the comparative study of yak and Tibetan sheep is not comprehensive.To solve this problem,a comparative study on the Grazing Methods of Tibetan sheep and yak was carried out.This study took the alpine meadow cold season pasture of Tianzhu Tibetan Autonomous County,Wuwei City,Gansu Province as the research object from 2020 to 2021.Under the condition of consistent vegetation before grazing and maintaining the same grazing intensity after grazing,the comprehensive effects of Grazing Yak,grazing Tibetan sheep+yak and grazing Tibetan sheep on Alpine meadow vegetation soil system were compared,To provide theoretical basis and practical guidance for the rational grazing and utilization of alpine meadow in Qinghai Tibet Plateau.The main research results are as follows:（1）The functional group biomass of Grazing Yak was the highest,and the dominant species was K.humilis,with a relative importance value of 0.190;The biomass of Gramineae in Tibetan sheep+yak treatment functional group was the highest,and the dominant species were E.nutans and Stipa purpurea,with relative importance values of0.175 and 0.110 respectively;The biomass of Gramineae in the functional group of grazing Tibetan sheep was the highest,and the dominant species were E.nutans,Stipa purpurea and Leymus secalinus,with relative importance values of 0.172,0.161 and 0.108 respectively.（2）Grazing Yak,grazing Tibetan sheep+yak and grazing Tibetan sheep were beneficial to the increase of density,crown width and height of K.humilis,respectively.The biomass of K.humilis is distributed most in rhizomes and least in seeds,which shows the growth mode that the nutritional efficiency is greater than the reproductive efficiency,and the storage efficiency is greater than the growth efficiency.Grazing Yaks is more conducive to the vegetative growth and sexual reproduction of K.humilis.Grazing Tibetan sheep was more conducive to the sexual reproduction of E.nutans,and the seed yield reached 86.85kg·ha^-1.The treatment of mixed grazing Tibetan sheep and yak is more conducive to the nutritional growth of E.nutans.The treatment of Grazing Yak has the worst growth of E.nutans,the treatment of grazing Tibetan sheep has the highest effect of sexual reproduction,and the treatment of mixed grazing Tibetan sheep and yak has the highest effect of nutritional reproduction.The effects of different livestock grazing on the reproduction of K.humilis and E.nutans clarify the causes of grassland vegetation succession caused by long-term grazing of different livestock from the perspective of dominant forage reproduction,which provides a new perspective for the study of alpine meadow vegetation succession.（3）Grazing Yaks increased soil bulk density and compactness,and grazing Tibetan sheep increased soil water content;Soil organic matter,total nitrogen,total phosphorus,total potassium,available nitrogen,available phosphorus and available potassium were the highest in grazing Tibetan sheep;C:N,N:P and C:P had no significant difference in each treatment;The activities of catalase,urease,protease,FDA hydrolase（fluorescein diacetate hydrolase）,cellulase and sucrase were the highest in grazing Tibetan sheep,The neutral phosphatase activity of Grazing Yak was the highest,reaching 2.67-3.84 mg/g/d.Soil structure and nutrient status are closely related to vegetation growth and soil health in grassland ecosystem.Compared with the treatment of Grazing Yak and grazing Tibetan sheep+yak,grazing Tibetan sheep is more conducive to the virtuous cycle of carbon source function and soil nutrients in alpine meadow ecosystem,which provides a guarantee for the sustainable grazing utilization of alpine meadow.（4）Different livestock combination grazing changed the abundance of soil dominant microorganisms.The bacteria with high abundance in each grazing treatment were Actinobacteria,Proteobacteria,Acidobacterita,Chloroflex,Firmicutes et al.;Fungi with high abundance include Ascomycota,Basidiomycota and Mortierellomycota,unclassified＿Fungi and Rozellomycota et al.The dominant soil bacterial strain is unclassified＿67-14,Vicinamibacter,Solirubrobacter,unclassified＿Kd4-96,Bacillus et al;The dominant soil fungi are Mortierella,Archaeorhizomyces and unclassified＿Ascomycota,Clavaria and other species have different abundances in grazing plots with different livestock combinations;The results of PCo A and NMDS analysis of bacterial and fungal communities showed that grazing different livestock caused great differences in soil microorganisms;Lefse analysis showed that the bacteria causing the differences among communities were g＿Nocardioides,f＿Xanthobacteraceae,o＿Gaillales et al.;p＿Basidiomycota,g＿Archaeorhizomyces and f＿Archaeorhizomyceteae et al.The correlation analysis between microorganisms and soil physical and chemical properties showed that soil FDA hydrolase activity,urease activity,protease activity and soil p H were the main factors affecting soil microbial bacterial community and fungal community.（5）The comprehensive analysis and ranking of vegetation soil microorganism related data show that grazing Tibetan sheep is more conducive to the grazing and utilization of alpine meadow,followed by grazing Tibetan sheep+yak,and Grazing Yak is the worst.In conclusion,the effects of different livestock combination grazing conditions on vegetation characteristics,soil characteristics and soil microbial characteristics of alpine meadow are different.The change of dominant forage breeding strategy directly affects the change of vegetation community structure,and then affects the soil characteristics and the composition and diversity of microbial community in soil.This process is not one-way,but in the long-term grazing process,resulting in the differences of vegetation soil system of three different livestock combinations.From the perspective of grassland productivity and ecosystem health,grazing Tibetan sheep in cold season is more beneficial to the alpine meadow of Qinghai Tibet Plateau.