Plant Community Stoichiometry Response To Degradation Of Different Grassland Types On Qingzang Plateau

The Qingzang Tibet Plateau is known as the "roof of the world",its fragile and sensitive ecological environment has led to a particularly serious problem of grassland degradation.Alpine steppe and meadow are the main types of grassland on the Qingzang Plateau and are important components of the alpine grassland ecosystem.The study of plant stoichiometry and its influencing factors along different degradation gradients in alpine grasslands and meadows is beneficial to the in-depth understanding of carbon,nitrogen,and phosphorus cycling processes in alpine ecosystems.Studies on degradation stoichiometry in alpine grasslands have mostly focused on soil ecosystems,and the response of plant nutrients and stoichiometry to degradation has been less reported.In this study,two types of grasslands(alpine grassland and meadow)on the Qingzang Plateau were used to investigate the changes in the ecological stoichiometry of plant communities along different degradation gradients and the dominant factors through the analysis of plant community stoichiometry,plant community characteristics,and soil physicochemical properties.The aim was to provide a scientific basis for the restoration and management of alpine meadows on the Tibetan Plateau.The main results are as follows.(1)Plant communities C,P,and C/N showed a decreasing trend,plant communities N,C/P,and C/P showed an increasing trend during degradation in alpine steppe and meadow on the Tibetan Plateau,and the C,N,and P contents of alpine meadow plant community were significantly higher than those of alpine grassland(P<0.001).The steady-state ranks of C,P,C/N,C/P,and N/P of alpine meadow plant communities were higher than those of alpine meadows during degradation.(2)Correlation results showed that C/P and N/P of alpine meadow grasses and C/P and N/P of sedge family were not correlated with plant community nutrients and stoichiometry.There were significant correlations(P<0.05)between plant community nutrients and stoichiometry and all functional community nutrients and stoichiometry during alpine meadow degradation.Plant community C,P,and C/P were significantly positively correlated(P<0.05)with soil organic carbon,total nitrogen,total phosphorus,C/N,N/P,C/P,and soil water content,and negatively correlated(P<0.05)with soil bulk density and pH in both meadow types.Total N,C/P,and N/P of plant communities showed opposite trends.Shannon-Winner diversity index and species number of alpine steppe plants during degradation were not correlated with plant community C,P,and N/P.Plant communities C,P,and C/N were significantly and positively correlated with cover,Pielou index,Simpson index,aboveground biomass,belowground biomass,and functional group biomass(P<0.05),meanwhile plant communities N,C/P,and N/P showed opposite trends.For meadows,plant community C,P,and C/N were significantly positively correlated with cover,ShannonWinner diversity index,number of species,Pielou index,Simpson index,aboveground biomass,belowground biomass,and functional group biomass(P<0.05),and plant community N,C/P,and N/P were significantly negatively correlated with the above indicators plant community N content,C/P,N/P of plant communities were significantly negatively correlated with the above indicators.(3)RDA redundancy analysis showed that aboveground biomass of cyperaceae and grasses N/P were the highest contributing functional group factors in alpine grassland and alpine meadow,with 97.2% and 97.6%,respectively.Soil bulk and soil total N were the highest contributing soil physicochemical property factors in alpine steppe and alpine meadow with 93% and 93.8%,respectively;belowground biomass and aboveground biomass of the community were the highest contributing plant community factors with 95.2%and 93.2%.