| In the global warming process,the Qinghai-Tibet Plateau,known as“The Roof ridge of the world”and“Water Tower of Asia”,is considered to be one of the most sensitive areas to global climate change and has attracted much attention.Previous research has shown that since the 20th century,the Qinghai-Tibet Plateau is experiencing an unprecedented warmer and wetter.In this process,as the main vegetation type of the grassland ecosystem on the Qinghai-Tibet Plateau,the response of alpine meadow to the precipitation increase will largely reflect the future development and adaptation trend of the grassland ecosystem on the Qinghai-Tibet Plateau.Therefore,it has been considered to be an ideal place to explore the response characteristics and mechanisms of alpine grassland ecosystems on the Qinghai-Tibet Plateau to climate change.However,many of the current researches on the influences of the precipitation increase on the alpine meadows only focused on a certain component of the ecosystem,rather than the whole ecosystem.There is relatively insufficient on the knowledge of the alpine meadow plant-soil system to precipitation increase.Therefore,an in-situ precipitation simulation experiment with five precipitation levels was conducted after analyzing the precipitation characteristics of the study area from 1997 to 2017.The present research aimed to address the following questions:1)How did the alpine meadows’plant diversity,productivity and coverage respond to precipitation increase?2)How did the soil physicochemical characteristics,nutrients and their stoichiometry,nutrient mineralization rate,and soil organic carbon and nitrogen components respond to it?3)How did the soil microbial biomass and enzyme activity respond to it?4)Under the background of precipitation increase,how did the alpine meadow vegetation,soil,and microorganisms interact with each other to maintain the development of the alpine meadow ecosystem?The results showed that:（1）The above-ground productivity and coverage increased significantly with the precipitation increase levels,whereas the Shannon-Wiener and Simpson diversity trended to the similar between different precipitation levels.The dominance of the Cyperaceae functional group showed an increasing trend,while the Gramineae declined slightly,and there was no significant change in the dominance of legumes and weeds.Short-term precipitation increase has no significant impact on the phylogenetic diversity and phylogenetic structure indexes（PD,MPD,MNTD,NTI,NRI）of alpine meadows.（2）With the precipitation levels increase,soil water content,TN,N ammonification rate,and mineralization rate show an upward trend,especially in the surface 0-10cm soil,while the available N（NH4+–N,NO3-–N）gradually decline.Soil bulk density,p H,TOC,TP,and soil C:N:P ecological stoichiometry have no obvious response to short-term precipitation increase.（3）Soil physical and chemical properties and nutrient contents increased or decreased significantly in the middle of the plant growing season（July）.With the extension of the experimental year,the soil water content,TN,TP,N:P,NH4+–N,and NO3-–N in the second year were higher than the initial of the experiment,especially for W25 and W50 treatments.（4）Compared with the response of soil TOC and TN to precipitation levels,soil organic carbon and nitrogen components of alpine meadows were more sensitive to the increase in precipitation.Overall,soil physical and density components of soil organic C and N differed significantly.However,they changed irregularly to the precipitation levels,especially at 0-10cm soil depth.（5）The order of TOC and TN contents in soil aggregates of different particle sizes was:macroaggregates≈microaggregates>free silt and clay particles.The order of TOC and TN contents in different soil density components was:light fractions>heavy fractions>soil aggregates fractions.The precipitation increase had a certain effect on improving the stability of soil aggregates in alpine meadows.Under W50 treatment,the MWD and GMD of soil aggregates were significantly higher than the control treatments.（6）With the increase of precipitation levels,the content of MBC and MBN showed an increasing trend in 0-20cm soil（p<0.05）,but the MBC:MBN did not change significantly.The precipitation increase obviously affects the soil enzyme activities involved in the hydrolysis cycle of carbon,nitrogen and phosphorus nutrients,but different soil hydrolytic enzymes have different response trends to changes in precipitation levels.（7）The RDA results showed that alpine meadow plant community characteristics significantly related to soil physicochemical environment,nutrients,and soil microbial characteristics,especially the relationships between the productivity,coverage,functional group dominance of alpine meadow and soil water content,available N contenrs,mineralization,ammoniation rate,and the activity of related enzymes.Under the background of precipitation increase,the increase in soil water content induced the changes in soil mineralization,ammoniation rate,and available nutrient content,which in turn promoted the changes in soil microbial biomass and enzyme activities.This might the potential reasons resulting in the changes in plant productivity,coverage,and the dominance of plant functional groups in alpine meadow.In conclusion,the present research initially revealed the response characteristics and the potential mechanisms of alpine meadow plant productivity,coverage,the dominance of plant functional groups,soil physicochemical status,and microbial characteristics and their interactions to the increased precipitation.The results may provide the supplement and reference for understanding and revealing the impacts and mechanism of increased precipitation of the alpine ecosystem on the Qinghai-Tibet Plateau under the warmer and wetter climate.In addition,it may also provide scientific guidance for the sustainable development and scientific management of the alpine ecosystem in the future. |
