Assessing The Positive Interaction Of Alpine Cushion Plant And Its Impact On Species Diversity

Alpine ecosystem is an important component of the earth's ecosystems,it provides a place to survive and reproduction for many plants and animals.Moreover,more than 40%of global population rely on the water which alpine ecosystem stores.As a foundation species of alpine ecosystem,alpine cushion plant plays a very important role in stability and maintenance of alpine ecosystem.Alpine cushion plant usually has unique morphological structures and growth patterns,so they often have positive interactions on other plant species in community,and promote the survival and growth of other plants.We assessed the positive interactions of Rhodiola rosea and Thylacospermum caespitosum at the levels of species,functional groups and communities,and their impacts on community species diversity at two sites.Results showed that:1)Rhodiola rosea did not have obvious positive interactions upon other plant species at the community level while Thylacospermum caespitosum did,and the positive interactions of Thylacospermum caespitosum did not increase with stress.2)Rhodiola rosea had positive interactions upon graminoids and leguminous,but it had negative interactions upon forbs;Thylacospermum caespitosum had positive interaction upon leguminous,and its positive interaction upon graminoids enhanced at the functional group level along the stress gradient,while its positive interactions upon forbs weakened.3)At the species level,the percentage of significant positive interactions of Rhodiola rosea(27.3%)was less than Thylacospermum caespitosum(42.9%),and the percentage of significant positive interactions of Thylacospermum caespitosum decreased along the stress gradient(from 42.9%to 37.5%),what's more,negative interactions occured under higher stress;We also found that the positive interactions of Rhodiola rosea upon other plants had no correlations with the average elevation of species' distribution,but the positive interaction of Thylacospermum caespitosum upon other plants declined along with the average elevation of species' distribution,which indicates that the positive interactions of cushion plants are species-specific.4)In Qilian Mountains,although the species diversity wasn't increased by the positive interactions of Rhodiola rosea,the positive interactions of Thylacospermum caespitosum did increase species diversity,and along with the increase of the stress,the impact of Thylacospermum caespitosum on species diversity gradually weakened.In a word,our research demonstrated the importance of alpine cushion plant'facilitation in the alpine ecosystem.Studies of positive interactions of different cushion plants,can help us better understand the positive interaction.The important roles of positive interactions on community construction and species diversity,may contribute to restoration and protection of alpine ecosystems.