Effects Of Grazing Regimes On Plant And Pollinator Communities And Their Interaction Networks In Grassland On The Qinghai-Tibet Plateau

In the Qinghai-Tibet Plateau,grazing is an important way of grassland management,and its role in altering the function of the grassland ecosystem has received extensive attention from researchers.Currently,most of studies focus on the effect of grazing regimes on the structure and the diversity of plant community.The variation of plant diversity is closely related to the diversity and pollination function of pollinators.However,there are few studies that focused on the effects of grazing regimes on pollinator diversity and plant-pollinator interaction.Understanding the diversity of plant and pollinator communities and their role in structure of pollination network of grassland ecosystem in the Qinghai-Tibet Plateau will shed light on the effects of grazing on community assembly and ecosystem function.In order to explore the effect of grazing regimes on the structure of pollination network of the grassland in eastern Qinghai-Tibet Plateau,we conducted the study in three consecutive years(2018-2020),selected alpine meadows and swamp meadows in eastern Qinghai-Tibet Plateau as the research objects.Sample plots for seasonal grazing(grazing prohibition in the growing season)and grazing throughout the year from alpine meadows.Sample plots of seasonal grazing,fencing for the whole year and grazing throughout the year were selected from the swamp meadows.We investigated the plant communities,pollinator communities and the pollination networks using transect method.From the perspective of the composition of the pollination network,we explored the effects of the grazing regimes on the structural characteristics of pollination network,and mainly answered following three questions:(1)In alpine meadows and swamp meadows,which grazing regime can maintain the species diversity of plant and pollinator communities and the functional diversity of flowering plant communities?(2)In alpine meadows and swamp meadows,whether grazing regimes affect the structure of pollination network?(3)How does the grazing regimes affect the structure of pollination network ?The main results in follows:(1)Compared with other grazing regimes,seasonal grazing increased the height and coverage of plant communities,advanced the abundance and species diversity of plants and pollinator community,but not affected,functional diversity of flowering plant community.(2)Seasonal grazing regime improved the interaction diversity of pollination networks in both grasslands,made the network more general,which increased the stability of the pollination network.(3)Structural equation model(SEM)shows that,in alpine meadows,seasonal grazing regime increased the diversity of pollinators by increasing the species richness and plant height of flowering plant community,and then reduced the specialization of the pollination network,made the pollination network more generalized and stable.In swamp meadows,on the one hand,seasonal grazing regime increased visitation frequency of pollinators directly,made the pollination networks more generalized.On the other hand,seasonal grazing regime increased species richness and functional diversity of flowering plant community,and indirectly enhanced visitation frequency of pollinators,to make pollination networks the network more generalized.In a word,in alpine grassland,the grazing regimes affected the structure of networks by affecting the species diversity of plant community and pollinator community and functional traits of flowering plant community.Our results suggest that seasonal grazing regime is conducive to maintaining the stability of the pollination network and thus to the stability of the structure and function of the grassland ecosystem.Therefore,the results of our study may also be useful for restoring degraded ecosystems,that is,in the degraded grasslands caused by overgrazing,the seasonal grazing regime can be adopted to facilitate the restoration of ecosystem functions such as pollination function.