Study Of The Relationships Between AM Fungi And Soil Microbial Community And Functions

Soil microbes are an important part of the ecosystem and determine the stability,diversity and ecological functions of the ecosystem.As one of the important soil microbes,arbuscular mycorrhiza(AM)fungi can associate with plant roots.AM fungi can promote the growth and the content of phosphorus and nitrogen of host plant,enhance the resistances of plant to disease and stress,increase plant diversity,change community structure,and maintain ecosystem and soil structure stability.However,there are few studies on how AM fungi affect soil microbial communities and functions,and even most of them are based on library inoculation experiments,lacking field investigation.Furthermore,soil nutrients enrichment could influence both AM fungal and soil microbial community and functions,but the research on the influence of AM fungi on soil microbes in that process is lacking.In order to further reveal the importance of AM fungi to belowground ecosystem,this study systematically researched the relationship between AM fungi and soil microbial community and functions through the methods of bibliometrics,field surveys,and simulated environmental changes.The main research contents and results are as follows:1.AM fungi increase the activities of soil enzymes.Soil enzyme activity is an important indicator of soil microbial metabolism and determing the nutrients cycling in soil.This study retrieved research articles on the effect of AM fungal inoculation on soil enzyme activity.Fifty six articles fitted the criteria,and 342 target observations were collected from these articles.The result of meta-analysis showed that AM fungi only significantly inhibited the activity of polyphenol oxidase(mean effect size =-0.425)and no significantly increase the activity of trehalase(mean effect size = 0.390),besides,AM fungi can significantly improve other 16 soil enzyme activities.AM fungi preferred to promote soil enzyme activity under low phosphorus and neutral pH conditions.There was a significant positive correlation between the response ratios of soil enzyme activity and plant biomass to the inoculation of AMF.These results indicate that AM fungi can promote soil microbial metabolic activity,which is influenced by the soil pH and available phosphorus concentration and coupled with the benefits of plant biomass from AM fungal inococulation.2.AM fungi were related with soil microbial community and carbon decomposition ability in revegetation condition.We collected 30 soil samples from a revegetation restoration pit in the hinterland of the Qinghai-Tibetan Plateau.The bacterial and fungal communities were investigated.The result of the correlation network showed that AM fungi were the most central fungal taxon at the levels of the class(degree = 11)and the family(degree = 15).The richness of soil fungi and bacteria was increased with the number of AM fungal reads,the fungal community was significantly related with the number of AM fungal reads,and the bacterial community was related to AM fungal colonization,extraradical hyphal length,and the number of reads.Soil aggregates were positively correlated with the AM fungal extraradical hyphae and the glomalin related soil protein(GRSP),which was normally secreted by AMF.The microbial carbon decomposition ability was significantly increased with the AM fungal colonization,extraradical hyphae and GRSP.This study demonstrated that under field conditions of the revegetation,AM fungi play as a keystone taxon of soil microbes,which is related to soil microbial diversity,community,and carbon decomposition ability.3.AM fungi mediated the influences of nitrogen addition on bacterial community and metabolic functions.We conducted a nitrogen addition(four different levels)experiment on the eastern edge of the Qinghai-Tibetan Plateau,and inhibited AM fungi by benomyl in each nitrogen addition plot.Benomyl could significantly inhibit AM fungal growth in roots and soil,and under no nitrogen addition condition,benomyl reduced the root length colonization by 56%,and the extraradical hyphal length by 48%.In control plots(without benomyl application),AM fungal colonization and extraradical hyphal length was decreased with the addition of nitrogen.Nitrogen addition increased both plant biomass and nitrogen content,which were further increased by inhibiting AM fungi.Meanwhile,nitrogen addition and inhibition of AM fungi could significantly affect plant composition,but only nitrogen addition could reduce plant richness,which was decreased by 32% in the highest nitrogen addition level.Nitrogen addition had no significant effect on bacterial community and diversity,but inhibition of AM fungi significantly changed the bacterial community composition,which also increased the relations of competition between bacteria.The index of bacterial metabolic functions and soil enzyme activity was significantly changed with the nitrogen addition level in control plots.The changes of plant communities,bacterial communities,and bacterial metabolic functions with nitrogen addition was significantly larger,while the change of plant growth characteristics was significantly lower,in control plots than AM fungi inhibited plots.These results indicate that AM fungi can expand the effects of nitrogen addition on plant communities,bacterial communities and metabolic functions,and guide the changes of soil enzyme activities following the nitrogen additions.Our studies reveal that AM fungi can significantly promote soil microbial metabolism activity,but this effect is related to soil phosphorus content and the ratio of plant biomass promoted by AM fungi.Under field conditions,AM fungi can service as a keystone taxon in revegetation restoration,and they are related to soil microbial community composition and carbon decomposition ability.We also find that despite the growth of AM fungi is decreased by nitrogen addition,AM fungi can also mediate the influences of nitrogen addition on soil microbial community and functions.In this study,the relationships between AM fungi and soil microbial community and function are researched,which can deepen our understanding of the function of AM fungi in belowground community and provide a new research avenue for AM fungi.