Mechanisms Of Climate Warming Affecting Coexistence Of Alpine Grassland Plants On The Qinghai-tibet Plateau

Frequent human activities worldwide have caused increasingly severe climate warming,which has profoundly affected the structure and function of grassland ecosystems.Many studies have found that climate warming causes the decrease in plant diversity and changes in community composition in grasslands(e.g.,grasses increase,and legumes and forbs decrease).However,an in-depth understanding of the complex mechanisms behind these phenomena is still lacking.As the “third pole of the world”,the Qinghai-Tibet Plateau’s unique alpine grassland ecosystem is rather susceptible to global warming.Therefore,it is of great importance to study the mechanisms underlying the responses of alpine grassland on the Qinghai-Tibet Plateau to climate warming.Under the framework of modern coexistence theory,this study used the data obtained from a warming competition experiment established at Haibei in Qinghai to fit the Ricker competition model to quantify the intrinsic growth rate(r),the niche difference(ND),and the fitness difference(FD,i.e.,competitive ability difference)of20 species representing four different functional groups(grass,sedge,forb,and legume)under control and warming treatments,and combined plant traits,light asymmetric competition,and allometric growth to delve into the effect of climate warming on coexistence of alpine grassland plants and its mechanisms.The results show that:(1)Warming significantly increased r of grasses but decreased r of the other three functional groups.In addition,warming significantly reduced ND among most species but sharpened FD(making grasses more competitive than other functional groups but legumes less competitive than other functional groups).It can be seen that the effect of warming on these population-level parameters favors grasses,but disfavors legumes and forbs,which is consistent with the changes in the relative abundance of different functional groups after warming found in many previous studies;(2)Warming decreased soil surface water content,changed plant traits(height,canopy width,and leaf area dropped significantly in the face of competition by grasses),light resources obtained and height scaling exponent of plants in different functional groups(grasses have the least reduction in light resources,and the height scaling exponent of legumes was greatly reduced);(3)The biological characteristics described above determined r and FD of species,and the relationship generally strengthened after warming,and changes in these characteristics from the control to warming generally explained the changes in r and FD.This shows that individual biological characteristics are the biological basis of population growth ability,species competition and coexistence relationships,and their from-control-to-warming changes.The above important findings have deepened our understanding of the impact of climate warming on the coexistence of grassland plants and the response mechanism of grassland communities to climate warming.This will help provide theoretical support and prediction methods for changes in the diversity and structure of grassland plant communities under climate warming and provide theoretical support for the protection of grassland biodiversity under the background of climate warming and the development of relevant applied research.