Influence Of Several Environmental Factors On AM Fungal Community Structure And Functioning In Alpine Meadow

Human activities have intensified global changes and lead to changes in the structure and function of ecosystems.The direction,degree,and mitigation strategies are the main topics that scientists are concerned about.In the past years,most studies have focused on how terrestrial ecosystems respond to global changes.Little is known about the diversity and function of soil microbes,especially arbuscular mycorrhiza(AM)fungi,which can form symbionts with most plants.As the linking of the above-ground and below-ground ecosystems,AM fungal diversity and community structure can directly affect various processes of terrestrial ecosystems.In the recent years,the issue of global change has become increasingly prominent,how will the community structure of AM fungi be affected?Are the ecological functions of AM changing with global change?Does the change in community structure of AM fungi cause changes in their ecological function?These questions have not yet been answered scientifically and comprehensively.Based on the above problems,long-term simulated warming and nitrogen deposition experiments were set up on the Qinghai-Tibet Plateau in this study.Combined with greenhouse inoculation experiments,this study systematically studied the changes of AM fungal community structure and function under global changes.The main results of this dissertation are listed below.1.In the central part of the Qinghai-Tibet Plateau,4 years of artificial warming and snow addition did not alter the root length colonization(%RLC)of AM fungi,the average%RLC was 20.9%.On the eastern Qinghai-Tibet Plateau,nitrogen addition significantly reduced the%RLC both in mixed roots and Elymus nutans roots systems.Based on the clone library,21 AM fungal virtual taxa(VT)were obtained in the first study,and 98 AM fungal VTs were observed in the second study with high-throughput sequencing.AM fungal richness,phylogenetic diversity and community structure were not influenced by artificial warming,snow addition and their interactions significantly.Nitrogen addition significantly increased AM fungal VT richness and community composition in mixed roots.In E.nutans roots,the diversity of AM fungi was not influenced by nitrogen addition,and only the high level of N addition changed the AM fungal community composition.The community composition of AM fungi was significantly affected by plant species diversity and soil factors such as nitrogen and phosphorus availability.2.The responses of AM fungal function to nitrogen addition at the plant community level and at the single species level were investigated by field treatment with benomyl and greenhouse inoculation,respecitively.The results showed that the increase of soil available nitrogen content induced the occurrence of parasitism in AM symbiosis.At the plant community level,the mycorrhizal growth response and mycorrhizal phosphorus uptake response of plants were significantly affected by nitrogen addition,which showed the quadratic relationship with N addition,and were significant negative at the highest level of nitrogen addition.The mycorrhizal nitrogen uptake response was significant negative under control and highest level of N addition,but not under other treatments.At the level of single species in the greenhouse,mycorrhizal growth,nitrogen uptake and phosphorus uptake response were all significantly reduced with the increase of nitrogen addition.They were all significant positive under control treatment and gradually decreased with nitrogen addition,eventually became significant negative effects under the highest level of N addition.The functional changes of the AM fungi are significantly related to the community structure of the specific AM species or genera.In conclusion,the different global changes have different effects on the diversity and ecological functions of AM fungi.Regional environmental characteristics and climate change characteristics both affect the response of AM fungi to global change.This study increased our understanding of the response of AM fungi under global changes and provided corresponding research ideas for further research on the changes of AM fungi community function.