Effects Of Seasonal Grazing On The Relationship Between Alpine Meadow And Yak

Grazing manages more than half of the world’s terrestrial ecosystems,produces20.53% of livestock products,supports 20.03% of the population livelihoods.The Qinghai-Tibetan Plateau is one of the largest continuous grasslands in the world,where alpine meadow accounts for 46.67%,and it is one of the most sensitive terrestrial ecosystems to grazing in the world.The interaction between alpine meadow and yak plays an important role in the grassland ecosystem in terms of the ecological service function.However,the effects of seasonal yak grazing on the relationship between alpine meadow and yak are still poorly understood.Thus,yak grazing experiments were carried out in summer,autumn,winter and spring in Maqu Grassland Agricultural Experimental Station of Lanzhou University to explore the effects of seasonal grazing on alpine meadow community structure,yak grazing behavior,nutrient digestibility of herbage and relationship between grass and livestock.The main results are as follows:1.Effects of yaks seasonal grazing on the community structure of alpine meadowFrom 2019 to 2020,the above-ground biomass of alpine meadow in the summer,autumn,winter,and spring grazed communities were 4545.86 kg/ha,3392.80 kg/ha,3466.93 kg/ha,and 3426.80 kg/ha,respectively,with spatial coefficients of variation17.61%,4.18%,5.46%,and 6.94%,respectively.However,from 2020 to 2021,the above-ground biomass of alpine meadow in the summer,autumn,winter,and spring grazed communities were 3263.60 kg/ha,2933.47 kg/ha,3395.47 kg/ha,and 3877.47kg/ha,respectively,with spatial coefficients of variation 9.31%,6.70%,2.45%,and14.27%,respectively.Moreover,from 2019 to 2021,the distribution pattern of aboveground biomass of different functional groups in the alpine meadows was in this order;Cyperaceae > Gramineae > Leguminosae.From 2019 to 2020,the spatial coefficients of variation of above-ground biomass of Cyperaceae and Gramineae were 8.88% ～29.09% and 16.93% ～ 25.34%,respectively,while they were 4.13% ～ 23.40% and27.02% ～ 74.19%,respectively from 2020 to 2021.From 2019 to 2020,the ShannonWiener,richness,and evenness were the highest in the summer grazed communities and the lowest in the spring grazed communities during.Yet,Shannon-Wiener index,Simpson,and evenness were the lowest in the autumn grazed communities from 2020 to 2021.Furthermore,Shannon-Wiener and evenness were positively correlated with the above-ground biomass and negatively correlated with the above-ground biomass of Gramineae（i.e.,grass forage biomass）.2.Effects of yaks seasonal grazing on behavior of yaksThe average daily feeding time,walking,and rumination/rest time of yaks in the summer,autumn,winter,and spring grazed communities were 519.78 ～ 522.44 min,33.04 ～ 69.78 min,and 79.19 ～ 82.74 min,respectively.From 2019 to 2020,yaks had the highest number of feeding bites in the spring grazed communities and the highest number of walking steps in the winter grazed communities.Yaks had the longest feeding time in the autumn grazed communities and the most frequent defecation in the summer grazed communities from 2020 to 2021.Seasonal grazing explained 48.0%,38.0%,27.0%,and 51.0%,50.2% of the number of bites,walking steps,feeding time,rumination time,and dry matter intake of yaks,respectively.The effect size of aboveground biomass and gramineous forage biomass to the number of walking steps of yaks were 34.8% and 18.0%,respectively.The effect size of edible forage biomass,gramineous forage biomass,and sedge forage biomass to the number of bites were30.0%,21.0%,and 21.0%,respectively.3.Effects of yaks seasonal grazing on the nutrient digestibility of yaksFrom 2019 to 2020,yaks had the highest dry matter digestibility（DMD）in the autumn grazed communities and the lowest in the spring grazed communities during the four grazing seasons.In summer 2019,the organic dry matter digestibility of forage（OMD）of yaks was 82.72%,which was 8.41% and 9.93% higher than the OMD in the winter and spring razed communities,respectively,and the crude protein digestibility（CPD）was higher in the summer grazed communities.In 2020,OMD of forage in spring was 8.80% and 13.32% lower than in summer and autumn,respectively.Yaks had the lowest total energy intake in the summer grazed communities.Yaks had the highest metabolizable energy/total energy in the autumn grazed communities,which was 10.14%,11.59%,and 5.80% higher than that in the spring,summer,and winter grazed communities,respectively.Forage quality and walking steps contributed 52.0%and 33.0% to DMD,respectively.The effect size of the above-ground biomass,sedge forage biomass,and grass forage biomass to yak fecal energy were 16.0%,26.0%,and11.0%,respectively.4.Effect of yaks seasonal grazing on alpine meadow-yak relationshipFrom 2019 ～ 2020,the alpine meadow-yak coupling relationship was 0.84,0.78,0.78,and 0.74 for the four grazing seasons of summer grazing,autumn grazing,winter grazing,and spring grazing,respectively,with the highest alpine meadow-yak coupling degree in summer grazing and the lowest in spring grazing.