Effects Of Simulated Warming And Nitrogen Addition On The Soil Bacterial Community Diversity In Alpine Swamp Meadow Of The Qinghai-Tibet Plateau

As important phenomenon of global climate changes,global warming and increasing deposition of atmospheric nitrogen have large impacts on the structure and function of terrestrial ecosystems.The Qinghai-Tibet Plateau is the largest and highest low-middle latitude permafrost region in the world,and is believed to be more sensitive area of climate change than the other areas,owing to the unique geographical position and special climate system characteristics.Under the stress of global climate change,the fragile ecosystems of the Tibetan Plateau are undergoing profound changes.Alpine swamp meadow on the Tibetan Plateau is a particularly sensitive ecosystem.As the major decomposer,microbial community played a vital role in soil biogeochemical cycling,microbial biogeochemical processes are sensitive to both climate warming and N deposition.Studying the effects of simulated warming and nitrogen addition on the soil bacterial community diversity in alpine swamp meadow of the Qinghai-Tibet Plateau,in order to provide reference for soil carbon and nitrogen cycle and protection of the high latitudes and high altitudes ecosystems under future global climate change scenarios.In this study,Experiments were conducted in alpine swamp meadow of the Fenghuoshan area on the Qinghai-Tibet Plateau,with warming simulated by using open-top chamber（0,1.5-2.5,3-5℃）,nitrogen deposition by nitrogen addition(0,5,10 g N·m^-2·yr^-1)and their interaction(1.5-2.5℃,0 g N·m^-2·yr^-1;0℃,5 g N·m^-2·yr^-1;1.5-2.5℃,5 g N·m^-2·yr^-1).Soil samples were collected from the 0-10 cm,10-20 cm and 20-30 cm soil layers under different warming and nitrogen addition treatments,high-throughput sequencing technology was used to analyze the16s r DNA region of soil bacterial responses to warming and nitrogen addition,and soil physicochemical properties,microbial biomass carbon and nitrogen were also examined.The main findings are as follows:（1）Under different warming and nitrogen addition treatments,the dominant bacterial phyla were Proteobacteria,Acidobacteria,Actinobacteria,Firmicutes and Gemmatimonadetes,suggesting that bacteria have a strong ability to sustain the structural stability of their own communities under different warming and nitrogen addition treatments.In the warming treatments:the relative abundance of Proteobacteria tended to initially increase and then decrease with the temperature increase.Acidobacteria abundance increased under high warming.Under different warming treatments,the relative abundance of Actinobacteria and Firmicutes decreased,and Gemmatimonadetes abundance increased.In the N addition experiment:the relative abundance of Proteobacteria tended to initially decrease and then increase with increasing nitrogen addition.Under different nitrogen addition treatments,the relative abundance of Acidobacteria and Gemmatimonadetes increased,Actinobacteria and Firmicutes abundance decreased.Under different warming and nitrogen addition treatments:the relative abundance of Proteobacteria increased under warming treatment,decreased under nitrogen addition and warming+nitrogen addition treatments.The relative abundance of Acidobacteria increased under nitrogen addition treatment,and the effect of warming and warming+nitrogen addition treatments were not obviously changes.Under different warming and nitrogen addition treatments,the relative abundance of Actinobacteria and Firmicutes decreased,and Gemmatimonadetes abundance increased.（2）Under different warming and nitrogen addition treatments,the bacterial diversity indexes tended to be decreased,but the overall difference was not significant.In the warming treatments:there were significantly reduced the Shannon and Simpson indices in the 10-20 cm layer compared with the control under high warming treatments（P<0.05）.High warming significantly reduced the Chao1 index in the 10-20 cm layer（P<0.05）,but was not dramatically affected the Chao1 index under low warming.In the N addition experiment:there were significantly reduced the Shannon index in the10-20 cm and 20-30 cm layers compared with the control under high nitrogen addition（P<0.05）.The Simpson index in the 20-30 cm layer significantly reduced under different nitrogen addition treatments（P<0.05）.The Chao1 index in the 10-20 cm layer significantly reduced under high nitrogen addition treatments（P<0.05）.The Chao1 index in the 20-30 cm layer significantly reduced under low nitrogen addition treatments（P<0.05）.Under different warming and nitrogen addition treatments:the Observed species,Shannon,Simpson and Chao1 indices in the 10-20 cm and 20-30 cm layers significantly reduced under warming+nitrogen addition treatments（P<0.05）.The Simpson index in the 0-10 cm and 20-30 cm layers significantly reduced under single warming treatment（P<0.05）.The Simpson index in the 20-30 cm layer significantly reduced under single nitrogen addition treatment（P<0.05）.（3）Under different warming and nitrogen addition treatments,soil bacterial communities were regulated by different soil factors.In the warming treatments:it was found that the main factors affecting soil bacterial community diversity were soil ammonium nitrogen and microbial biomass nitrogen.pH,total nitrogen,ammonium nitrogen,nitrate nitrogen,organic carbon,water content,microbial biomass carbon and nitrogen were significantly correlated with specific bacteria at phylum level（P<0.05）.In the N addition experiment:it was found that the main factors affecting soil bacterial community diversity were pH,soil ammonium nitrogen and water content.pH,total nitrogen,ammonium nitrogen,nitrate nitrogen,organic carbon,water content,microbial biomass carbon and nitrogen were significantly correlated with specific bacteria at phylum level（P<0.05）.Under different warming and nitrogen addition treatments:it was found that the main factors affecting soil bacterial community diversity were pH and ammonium nitrogen.there were significant relations between specific bacteria and pH,total nitrogen,organic carbon,water content,microbial biomass carbon and nitrogen.