| Grazing is the most common way of human disturbance to grassland,and it is an important factor affecting the grassland ecosystem.The grassland of Qinghai Tibet Plateau is vast,accounting for half of the whole plateau area,and there are various types of grassland.The nomadic people on the plateau mainly depend on yaks and Tibetan sheep for grazing for generations.Yaks and Tibetan sheep are not only their means of production,but also their means of life.The way they use grassland is mainly nomadic and seasonal grazing.In recent years,due to the increase of population and the change of production relations,unreasonable grazing management and the impact of global changes,grassland ecosystem disorder,grassland productivity decline,large area of grassland degradation.With the implementation of the concept of "great ecology",it has become restrained to simply graze and obtain endless animal products.People must use modern scientific management ideas,focus on ecology,and realize scientific and systematic grazing,that is,give full play to grassland resources and ensure the continuous stability of grassland structure and function.In this study,since the early summer of 2014,the grazing experiment was started.The local yak and Tibetan sheep were used as the grazing livestock,and the complete randomized block design was adopted.The experiment designed three blocks,each block including five different cattle and sheep grazing combinations and a control treatment(no grazing N0Y0),a total of 18 experimental plots.Two single grazing treatments(N1Y0 and N0Y2)and three mixed grazing treatments(1:2(N1Y2),1:4(N1Y4)and 1:6(N1Y6)were used in the combination of cattle and sheep grazing.The grazing intensity is designed as medium intensity,that is,the intake of livestock to aboveground plants is about 50-60% of the total aboveground biomass.The yak and Tibetan sheep used in the experiment were about 100 kg and 30 kg respectively.Through long-term grazing experiments in growing season,the differences of vegetation characteristics,soil physical and chemical properties and soil microbial community between different grazing methods under moderate grazing intensity were studied.The effects of Grazing Methods on the ecosystem functions of alpine grassland,and the effects of vegetation characteristics and soil physical and chemical properties on soil bacterial and fungal communities under grazing disturbance were clarified.The main conclusions are as follows:(1)There was significant difference in carbon using between grazing and non grazing grassland(P < 0.05).Grazing significantly(P < 0.05)increased the Mc Intosh index of 0-10 cm soil layer,but significantly reduced the Shannon Wiener index(P < 0.05).There was no significant difference in the metabolism of amino acids,alcohols,amines and acids among the treatments in the same layer(P > 0.05),but there was significant difference in the metabolism of sugars and esters(P < 0.05).(2)In the third year of grazing,there was no significant effect on the diversity index of bacteria(P > 0.05),but on the diversity index of fungi(P < 0.05).The increase of cattle proportion in grazing combination is beneficial to the increase of fungus ? diversity index.In the fourth year of grazing,the Shannon index of soil bacteria,Shannon index of fungi and Simpson index of fungi increased with the proportion of sheep in mixed grazing,and the index value decreased.There was no significant difference between grazing and control.The dominant groups of soil fungi are Ascomycetes,tubercle bacilli and basidiomycetes,and the relative abundance is more than 70%.After grazing,the relative abundance of tubercle bacteria increased,while that of basidiomycetes decreased(P < 0.05).Through the analysis of bacterial association network,it can be found that the relationship between fungi in the third year of grazing is also not as close as that between bacteria.Compared with the third year of grazing,bacteria and fungi in the fourth year of grazing are closely related to each other.Fungi and bacteria interweave together to form a complex symbiotic network.(3)Grazing reduced vegetation coverage,but there was no significant difference between Different Grazing Methods(P > 0.05).The results showed that grazing significantly reduced the aboveground biomass of vegetation(P < 0.05)in the fourth year(36% ? 52%)than in the third year(34% ? 48%),but there was no significant difference between Different Grazing Methods(P > 0.05).The results of two years showed that the underground biomass of vegetation increased under grazing treatment,but there was no significant difference between the two treatments(P > 0.05).The response of different vegetation functional groups to grazing is quite different,and the aboveground biomass of Cyperaceae and weeds tends to increase after grazing.However,the aboveground biomass of Gramineae and legume decreased significantly(P < 0.05),especially legume biomass,the above ground biomass decreased by 82% ? 92%,but there was no significant difference between Different Grazing Methods(P > 0.05).(4)The difference of soil physical properties is mainly reflected in 0-10 cm soil layer,and the difference of soil physical properties between different grazing ways is large.In general,single grazing of cattle and sheep can improve soil compactness,soil moisture and soil bulk density,while mixed grazing has the opposite trend.In the third year of grazing,there were significant differences in the content of total phosphorus and available nitrogen between Different Grazing Methods(P < 0.05),but there was no significant difference between the two treatments(P > 0.05).With the increase of the proportion of sheep and cattle in the mixture,the total phosphorus content of soil decreased.The results of the fourth year of grazing showed that grazing significantly changed the content of soil organic matter,total nitrogen,total phosphorus and available phosphorus(P < 0.05),but the feedback of the content to different grazing methods was inconsistent.(5)Grazing patterns have synergistic effects on plant features,soil physico-chemical properties,and soil microbial community. |
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