Responses Of Grassland Soil Microbial Community To Climate Warming Revealed By Metagenomics Approaches

Grassland is one of the most important terrestrial ecosystem types,providing goods and services to support human populations.Soil microorganisms as decomposers in the ecosystem played a vital role in driving soil biogeochemical cycles.The impacts of warming on soil microbial communities will undoubtedly affect these cycles.However,due to the complexity of soil microbial and the limitaion of research techniques,responses of soil microbial communities to warming in grasslands remained largely unknown.To explore changes of the taxonomic and functional compositions of soil microbial communities,we conducted warming experiments in three model ecosystem,a alpine grassland in Haibei,Qinghai,China,a semi-arid grassland in Duolun,Inner Mongolia,China and a semi-arid grassland near Stanford University,California,US.In this research,we used two metagenomic technologies,MiSeq sequencing and a microarray named GeoChip.We found that:(1)Responses of soil microbial functional structures were more sensitive to warming than taxonomic composition.(2)At thetaxonomic level,soil microbial communities had different response strategies in different ecosystems.In semi-arid grassland in Inner Mongolia(<1 ?,6 years),microbial taxonomiccomposition did not change significantly in response to warming.In semi-arid grasslands(1—1.5?,14 years)inCalifornia,the relative abundance of fast-growing bacteria such as Bacteroidessignificantly decreased,whereas the relative abundance of slow growing bacteria,such as Acidobacteria significantly increased.(3)At the functional gene level,different microbial functional genes also responded differently in different climate condition.In alpine grasslands,warming reduced carbon fixation,ammonification and denitrification gene abundances whereas enhanced nitrification gene abundances.In addition,N2 O flux positively correlated with nitrification gene amoA abundance,suggesting that nitrification was the dominant process for N2 O emissions.In the semi-arid grasslands of Inner Mongolia,the day-time warming increased phototrophic carbon fixation pathway(3HP and Calvin cycle),ammoniation and denitrification processes,whereas night-time warming and whole-day warming did not have significant impacts.In California semi-arid grasslands,long-term warming promoted anaerobic carbon fixation pathway(DC/HB and rTCA cycle),and increased gene abundances related to labile carbon degradation,indicating that long-term warming promoted the labile carbon turnover rates and inhibit the degradation of recalcitrant carbon.(3)Responses of soil microbial phylogenetic composition and functional structure were inconsistent,which might be attributed to the difference between their environmental driving factors.Microbial taxonomic composition was related to soil pH and vegetation,and the functional genes composition was more related to soil nutrients.In this study,we comprehensively analyzed the responses of soil microbial taxonomic composition and function structure to warming from three typical grasslands.Our results provide more clues for the accurate feedback of natural ecosystems to climate changes.