| Over the past century,human activities have increased greenhouse gas emissions,causing global warming,significantly increasing the amount of water vapor in the atmosphere,speeding up the global hydrological cycle,and changing global precipitation regimes.Changes in precipitation regimes can alter the characteristics of aboveground and underground communities in ecosystems and ultimately have a profound impact on the structure and function of ecosystems.Terrestrial ecosystems are multidimensional and capable of providing multiple ecosystem functions and services(i.e.ecosystem multifunctionality)simultaneously.Soil microbial communities,as the most complex and diverse biological communities on earth,play an important role in driving terrestrial ecosystem multifunctionality.However,current studies on the effects of precipitation regime changes on natural ecosystems have focused on plant communities,the understanding of soil microbial communities is still limited.In 2018-2020,precipitation regime changes simulation experiments,including summer drought,decrease half amount of precipitation,increase half amount of precipitation,and increase doubled frequency of extreme precipitation,were conducted in forest,grassland,and farmland ecosystems in Guanzhong area of Shaanxi Province.The study was aimed to explore the effects of different changes in precipitation regimes on soil microbial diversity,community composition,abundant and rare groups,co-occurrence network pattern,and soil physicochemical properties and ecosystem multifunctionality,analyse the relationships between soil microbial communities and ecosystem multifunctionality during the changes in precipitation regimes,and reveal the mechanism of precipitation regime changes in affecting soil microbial communities and ecosystem multifunctionality.The main results are as follows:Firstly,the study of summer drought conducted in forest,including natural precipitation and precipitation exclusion treatments,was mainly aimed to explore the dynamic change characteristics of soil microbial communities and ecosystem multifunctionality in five periods: early drought,end of drought,early recovery,intermediate recovery,and late recovery.Summer drought had significant impacts on microbial communities at the end of drought,increased bacterial alpha diversity,changed bacterial community composition,increased abundant and rare bacterial alpha diversity.Summer drought significantly increased the relative abundance of Actinobacteria and altered abundant and rare bacterial community composition at the end of drought and early recovery periods,and decreased the complexity and stability of bacterial co-occurrence networks at the end of drought,early recovery,and intermediate recovery periods.Biotic and abiotic factors had significant impacts on ecosystem multifunctionality,bacterial community composition had a direct and significant positive effect on ecosystem multifunctionality,and summer drought indirectly regulated bacterial community composition,ecosystem multifunctionality,and bacterial community composition-ecosystem multifunctionality relationship via affecting soil nutrients and p H.Secondly,the study of precipitation amount and precipitation frequency changes conducted in forest,including ambient precipitation,decrease half amount of precipitation,increase half amount of precipitation,and increase doubled frequency of extreme precipitation,was mainly aimed to focus on the response characteristics of soil microbial communities and ecosystem multifunctionality to different precipitation regime changes.The increase amount of precipitation and increase frequency of extreme precipitation significantly changed bacterial,fungal,rare bacterial,abundant fungal,and rare fungal community composition,and the decrease amount of precipitation,increase amount of precipitation,and increase frequency of extreme precipitation significantly increased the complexity and stability of microbial co-occurrence networks.Biotic and abiotic factors had significant impacts on ecosystem multifunctionality,bacterial community composition had a direct and significant positive effect on ecosystem multifunctionality,and precipitation regimes indirectly regulated bacterial community composition,ecosystem multifunctionality,and bacterial community composition-ecosystem multifunctionality relationship via affecting soil nutrients and p H.Thirdly,the study of the decrease amount of precipitation conducted in grasslands,including plant diversity(low plant diversity and high plant diversity)and precipitation(ambient precipitation and decrease half amount of precipitation)two-factor treatments,was mainly aimed to explore the change characteristics of soil microbial communities and ecosystem multifunctionality during the decrease amount of precipitation.The decrease amount of precipitation significantly increased fungi alpha diversity in grasslands with low plant diversity,changed bacteria community composition in grasslands with low plant diversity,increased abundant bacterial alpha diversity in grasslands with high plant diversity,changed abundant bacterial community composition in grasslands and rare bacterial community composition in grasslands with low plant diversity,decreased the complexity of bacterial co-occurrence network,and increased the complexity of fungal co-occurrence network.Biotic and abiotic factors had significant impacts on ecosystem multifunctionality,and fungal community composition had a direct and significant positive effect on ecosystem multifunctionality.Plant diversity had a direct effect on fungal community composition and ecosystem multifunctionality and also had an indirect effect on ecosystem multifunctionality by changing fungal community composition.Precipitation amount indirectly regulated ecosystem multifunctionality via influencing soil nutrients.Finally,the study of the decrease amount of precipitation conducted in farmlands,including winter cover crop(fallow,Vicia villosa Roth.,Lolium perenne L.,and Vicia villosa Roth.+ Lolium perenne L.)and precipitation(ambient precipitation and decrease half amount of precipitation)two-factor treatments,was mainly aimed to explore the shift characteristics of soil microbial communities and ecosystem multifunctionality during the decrease amount of precipitation.The decrease amount of precipitation significantly changed fungal community composition in farmlands with winter cover crop of high biomass and the composition of abundant fungal communities in farmlands planted with Vicia villosa Roth.The decrease amount of precipitation had no significant effect on the complexity of bacterial co-occurrence network in farmlands with fallow treatment,but significantly increased the complexity of bacterial co-occurrence network in farmlands with winter cover crop of low biomass,decreased the complexity of bacterial co-occurrence network in farmlands with cover crop of high biomass.Biotic and abiotic factors had significant impacts on ecosystem multifunctionality,and fungal community composition had a direct and significant positive effect on ecosystem multifunctionality.Winter cover crop had a direct effect on ecosystem multifunctionality and also had an indirect effect on fungal community composition through influencing soil nutrients and p H.Precipitation amount indirectly regulated fungal community composition,ecosystem multifunctionality,and fungal community composition-ecosystem multifunctionality relationship by affecting soil nutrients.Changes in precipitation regimes indirectly regulate microbial communities and ecosystem multifunctionality through influencing soil environmental factors.The responses of microbial communities and ecosystem multifunctionality to precipitation regime changes are as follows: co-occurrence network pattern and soil nutrients > community composition and ecosystem multifunctionality > abundant and rare groups > diversity.The effects of different precipitation regime changes on microbial communities and ecosystem multifunctionality are as follows: summer drought > increase frequency of extreme precipitation > increase amount of precipitation > decrease amount of precipitation.The responses of ecosystems to the decrease amount of precipitation are as follows: forest >grassland > farmland.The bacterial communities are dominant in the microbial communities of forest,while the fungal communities are dominant in the microbial communities of grassland and farmland.In conclusion,this study reveals the mechanism of different precipitation regime changes affecting soil microbial communities and ecosystem multifunctionality in different ecosystems,which provides an important theoretical basis for regulating natural ecosystems to adapt to future climate change. |
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