| Global climate changes,caused by human activities,will have significant impacts on global ecosystems,which have been gradually recognized by human beings.Global climate changes mainly include atmospheric nitrogen deposition addition,precipitation change and global warming.The effects of climate changes on terrestrial ecosystem usually manifest as the changes in productivity of and species diversity plant communities.Therefore,it is very important for us to study how plant community productivity and species diversity change under the global climate changes.The Tibetan Plateau is the largest and highest plateau in the world.One of the main vegetation types on the Tibetan Plateau is alpine meadow,which accounts for 16.22%of the total grassland of the Tibetan plateau.With extensive permafrost beneath the surface of alpine meadow that has developed for many centuries,alpine meadow on the Tibetan Plateau is very sensitive and vulnerable to global changes.This sensitivity and vulnerability are often characterized by grassland degradation,plant species decrease and the diminution of ecosystem functioning.We simulated precipitation change,nitrogen deposition and global warming to investigate the dynamics of plant community on Tibetan Plateau.Experimental treatments includ single factor treatments of altered precipitation,nitrogen addition and warming and two-factorinteraction treatments.We analyzed the data at three levels:community,functional group and species.Plants were divided into three functional groups:graminoids,leguminosae and forbs;four dominant species,Elymus nutans,Stipa aliena,Kobresia capillifolia and Anemone rivularis,were chosen for analyses at the species level.We measured soil water content,NH4+-N,NO3--N,microbial biomass carbon,microbial biomass nitrogen and pH of 0?10 cm and 10?20 cm,air temperature and aboveground biomass,coverage,species composition and diversity of plant community.The main conclusions of our study are as follows:1.Altered precipitation had no significant effect on community aboveground biomass,coverage,species height and abundance,but precipitation reduction significantly reduced Pielou evenness index of the community.This indicated that the plant community was more sensitive to precipitation reduction than precipitation increase,precipitation reduction can significantly reduce the species distribution uniformity of the plant community.2.Aboveground biomass and coverage of graminoids increased significantly under N addition,and aboveground biomass of the two dominant graminoid species,Elymus nutans and Kobresia capillifolia,also showed a significant increase,aboveground biomass of Leguminosae and forbs did not change significantly,which meant that graminoids were more sensitive to N addition than Leguminosae and forbs.However,N addition did not change the species diversity.The possible reason could be that N addition did not lead to the loss of species in the plant community,or that the duration of N addition was too short.3.Warming had no significant effect on community aboveground biomass,coverage and species diversity.There were two possible reasons:1)positive and negative effects caused by warming offset each other.Warming significantly increased the contents of soil available nutrient,meanwhile,it could also bring heat damage to plants;2)the duration of the warming treatment was too short.4.Interaction treatments including N addition significantly increased the aboveground biomass of plant community and graminoids.This increase in aboveground biomass was not found in other interaction treatments,indicating that effect of N addition played an dominant role in interactive treatments.In addition,plant community cover did not chang in interaction treatments.On the one hand,some interaction treatments did have no effect on functional groups,such as N&PI,W&PI and W≺on the other hand,the cover increase of graminoids might compensate the cover decrease of forbs,such as N&PR and N&W.Aboveground biomass,coverage and average height of Elymus nutans increased significantly in interaction treatments that included N addition,while abundance of Anemone rivularis showed a significant decrease in interaction treatments that included warming.Finally,N&W and W&PI both significantly reduced species number of the plant community,and reducing precipitation combined with warming could significantly decrease species diversity of plant communities on Tibetan Plateau. |
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