Effects Of Nighttime Warming And Precipitation Change On Soil Microbial Communities In Temperate Steppes Of Northern China

Grassland ecosystem,as the largest terrestrial ecosystem in China,plays an irreplaceable role in climate regulation,nutrient cycling and energy flow.By driving biogeochemical cycling,soil microorganisms play crucial roles in maintaining ecosystem functions and services.Their responses to climate change determine the feedback of grassland to climate directly.However,few studies focused on the interactive effects of multiple driving factors on microbial communities,resulting in unclear conclusions on the interactions between aboveground plant and belowground microbes under climate change scenarios.Using a unique soil monolith transplantation experiment simulating global warming and precipitation regime change,this dissertation investigated the effect of nighttime warming and precipitation change on soil microbial(bacteria,fungi and protist)composition and diversity in three steppe(desert,typical and meadow steppes)ecosystems in Duolun County,Inner Mongolia.The purposes were to reveal the response characteristics of soil microorganisms to climate change factors in different steppes,and important implications and reference for accessing the response and feedback mechanism of temperate steppe ecosystems to climate change in northern China were also extended.The main results of this study were as follow:(1)Nighttime warming significantly reduced soil respiration in meadow steppe,nitrogenase activity in three steppes,and the abundance of nitrogen-fixing bacteria nif H gene in typical and meadow steppes.Soil moisture,respiration and the abundance of nif H gene were negatively correlated with soil temperature.Nitrogenase activity,potential ammonia oxidation,denitrification enzyme activity,soil respiration,the abundance of nif H and nos Z1 genes were increased with the increasing soil moisture.These results indicate that increased soil temperature caused by nighttime warming and decreased soil moisture caused by nighttime warming or decreased precipitation strongly affect the functional activity of microorganisms,and may reduce the supply of nitrogen by biological nitrogen fixation to grassland ecosystem.(2)The diversity of soil microbial communities showed that the ?-and ?-diversity of bacteria,fungi and protist communities varied greatly among the three grasslands.Decreased precipitation reduced the diversity(phylogenetic diversity,PD)of bacterial and fungal communities.Nighttime warming increased the diversity of protist community,but no effect was found on the diversity of bacterial and fungal communities.Soil moisture was positively correlated with the diversity of bacterial community in desert and meadow steppes without nighttime warming.The diversity of protist community showed positive dependence upon soil moisture in three steppes,but the diversity of fungi community was not affected by soil moisture.However,under nighttime warming,the sensitivity of bacterial community diversity to soil moisture was enhanced in desert and meadow steppes,the sensitivity of fungal community diversity to soil moisture was enhanced in desert steppe only,but the sensitivity of protist community diversity to soil moisture was decreased in three steppes.Overall,the diversity of protist was more sensitive to water changes caused by decreased precipitation than bacteria and fungi.Nighttime warming could change the effect of moisture on microbial diversity to a certain extent,especially protist.(3)The main taxa of soil bacteria,fungi and protist in the three grasslands illustrated that the relative abundance of Actinobacteria showed a negative dependence upon soil moisture in desert steppe,the relative abundance of Mortierellomycota in fungi was not affected by soil moisture,but the relative abundance of Rhizaria in protist was positively correlated with soil moisture in meadow steppe without nighttime warming.The sensitivity of Actinobacteria and Mortierellomycota to soil moisture was enhanced,but the sensitivity of Rhizaria to soil moisture was reduced under nighttime warming.Analysis of LEf Se showed that there were more warming-sensitive taxa in the protist communities among the three grasslands.Alveolata enriched significantly in desert and meadow steppes,and Amoebozoa enriched in typical and meadow steppes.These results suggest that nighttime warming exacerbates the response of major bacterial and fungal groups to drought stress,but alleviates the negative effects of drought on protists.(4)Soil microbial network relationship revealed that nighttime warming increased the proportion of negative correlations in the desert and typical steppes compared to the microbial networks without nighttime warming,suggesting that nighttime warming made the network structure of soil microbial communities more stable in desert and typical steppes.Structural equation model(SEM)showed that plant biomass was positively correlated with the diversity of fungal community under nighttime warming plus decreased precipitation.Plant biomass was positively related to the diversity of bacterial community under nighttime warming plus increased precipitation.In addition,protist also had an indirect positive effect on plant biomass in grassland ecosystems,because of the preying of protest on bacteria and fungi.Overall,compared to bacteria and fungi,soil protist was more sensitive to climate warming and precipitation regimes changes in different grassland ecosystems.The balance of precipitation change and warming-enhanced evapotranspiration will determine the trends of soil microbes on climate change.These will affect the stability of microbial communities and elements cycle mediated by them,which will change aboveground biomass furtherly.This study is of great significance for understanding the effect of climate change on grassland ecosystems and predicting and aging climate change trends strategies.