| Arbuscular mycorrhizal fungi(AM fungi)are ubiquitous in grassland ecosystems which can form reciprocal symbiosis with most of terrestrial plants.AM fungi can help plants adapt to adversity environments.Soil microorganisms can regulate the interaction between plants and soil under global change conditions.The global changes(eg.warming and nitrogen deposition)caused by human activities(the consumption of fossil fuels and fertilization)have been influencing ecosystem stability.Global changes can not only directly or indirectly affect the structure and function of soil microbial communities,but also have a significant impact on the composition and stability of soil aggregates,thereby affecting soil organic carbon storage in the soil.So far,the influence of AM fungi on the soil microbes,aggregates and organic carbon storage of grassland ecosystems under global change is still unclear.In order to understand the effects of AM fungi on the soil microbial community structure,composition,stability of soil aggregates and soil organic carbon storage under warming and nitrogen(N)deposition,a 6-years field experiments(2015-2020)was conducted in Songnen grassland using infrared radiators to simulate elevated temperature,ammonium nitrate was added to simulate atmospheric N deposition,and benomyl(fungicide)was used to suppress the activities of AM fungi.The research results could help explain and clarify the mechanism how AM fungi improve the stability of grassland ecosystems under global change conditions.The main results are as follows:(1)Warming,N addition and benomyl addition treatments significantly affected the structure and composition of soil microbial community.When the benomyl treatment is not added,warming,N addition,and warming + N addition treatments increase the relative abundance of the Acidobacteria respectively;when benomyl is added,warming,N addition and warming + N addition treatments reduce the relative abundance of Acidobacteria respectively.However,when the benomyl treatment is not added,warming,N addition and warming + N addition treatments significantly reduce the relative abundance of the Proteobacteria respectively;when benomyl was added,the relative abundance of Proteobacteria was increased significantly by warming,N addition and warming + N addition treatments.The composition of soil bacterial community was significantly different between the treatments with and without benomyl addition.In the soil fungal community,significant differences in the abundance of Ascomycota and Basidiomycota were detected among warming,N addition and benomyl addition treatments.Compared with control,the relative abundance of Ascomycota was significant due to warming,N addition,benomyl addition and interaction,however,warming,N addition,benomyl addition,and interaction all significantly reduced the relative abundance of Basidiomycota.Benomyl addition significantly increased the PLFA content of soil bacteria and fungi.A significant interactive effects of warming,N addition and benomyl addition on the PLFA content of soil bacteria and fungi was observed.N addition significantly increased the total PLFA content,warming + N addition significantly reduced the radio of soil fungi to bacteria.(2)Under warming and N addition,the addition of benomyl had a significant impact on soil microbial diversity and microbial biomass.Benomyl addition,warming+ benomyl addition significantly reduced the species abundance of soil bacterial communities;under the conditions of warming and N addition benomyl had a negative impact on the species diversity of soil bacterial communities;N addition significantly increased soil fungal species abundance and diversity,there were significant differences in soil fungal species abundance among N addition,benomyl addition,and warming +N addition + benomyl addition,significant differences in soil fungal species diversity among N addition,warming + benomyl addition,and N addition + benomyl addition were also observed.Benomyl addition significantly increased soil microbial biomass C and microbial biomass N contents,while N addition significantly increased soil microbial biomass N content,and there was a significant interactive effect between warming,N addition and benomyl addition on soil microbial biomass N content.(3)RDA analysis showed that soil organic carbon(SOC),dissolved organic nitrogen(DON)and available nitrogen are the main factors affecting the composition of soil bacterial communities.Soil water content,organic carbon,available nitrogen,and DON are the main factors that affect soil fungal community composition.(4)Under warming and N addition,benomyl addition had a significant positive effect on the proportion of soil aggregates of each particle size and the average weight diameter.Under warming,N addition and warming + N addition,benomyl addition significantly increased the percentage of large aggregates and average weight diameter,while the percentage content and average weight diameter of silt + clay decreased significantly;warming significantly reduced the percentage of micro-aggregates and the average weight diameter,but significantly increased the percentage of silt + clay and the average weight diameter.(5)Under warming and nitrogen addition,benomyl addition significantly increased SOC content and organic carbon storage.Under without benomyl addition,warming,nitrogen addition,and warming + nitrogen addition treatments had no effect on the SOC content and organic carbon storage;under benomyl addition,warming,nitrogen addition and warming + nitrogen addition increased the SOC content and organic carbon storage,there were significant differences between the treatments with and without benomyl additions.The results showed that the response of soil bacteria to AM fungi is more sensitive than soil fungi under warming and N addition in Songnen grassland.Under warming and N addition,AM fungi might affect soil and soil microbial community structure and composition.The formation and stability of soil aggregates provides the physical protection for soil carbon,reduces the interference and degradation of soil carbon by microorganisms,thereby increasing soil carbon storage and improving soil carbon sequestration capacity.Therefore,the results of this study are helpful to evaluate the impact of AM fungi on grassland management on soil carbon sequestration potential under warming and N deposition. |
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