Effects And Mechanisms Of Simulated Herbivore Foraging On Soil Microbial Community In Grassland

Soil microbes are important for grassland ecosystem functions,such as nutrients cycling,organic matter turnover and maintaining soil physical structure.With the development of molecular biology techniques,the relationship of herbivores and soil microbes has become research topic of ecologists in recent years.Using soil bacteria and fungi as representatives of soil microbes,we researched the characteristics of soil microbial community in plant functional group treatments and clipping treatments.Combined with soil physical and chemical properties and plant community characteristics,this study aimed to find the main pathways and key drivers of herbivore foraging influencing soil bacterial and fungal community.This research could provide the theory evidence for understanding the linkages between aboveground and belowground communities.Leymus chinensis and Kalimeris intergrifolia were plant materials in this study.Two independent experiments were conducted in Songnen Grassland Research Station.Plant functional groups were controlled variables in one experiment lasting two plant growth seasons,and clipping treatments were controlled variables in another experiment lasting two months.Hi Seq 2500 sequencing technology and real-time quantitative PCR technique were adopted to identify soil bacterial and fungal diversity,composition and biomass.Based on controlled experiments simulated herbivore foraging,major results and conclusions we obtained in this study were as follows:(1)Soil bacteria were absolutely dominant in both experiments.There were significant effects of clipping on soil microbial biomass.Results showed that the gene copies of bacteria in none clipping treatment were higher than those either in grasses clipped or forbs clipped treatments by 1.37 × 109± 1.47 × 109copies/g dry soil,and these changes resulted from corresponding soil organic carbon contents.(2)Soil bacterial Shannon-Winner index and Pealou evenness index were significantly different between plant functional group treatments,among them the forbs' diversity index was about 60 percent of grasses and mixture treatments.Soil moisture was the main causes of these changes.(3)The effects of plant functional groups on soil bacterial community composition were different obviously.The redundancy analysis results showed that plant root: shoot ratio was one of the key drivers.The relative abundance of Gemmatimonadetes and Crenarchaeota in the grasses were higher than forbs.(4)Individual groups of bacteria and fungi responded differently to clipping.For example,Firmcutes and Gemmatimonadetes were only phyla which were sensitive toclipping by the changes of soil organic carbon and nitrogen contents.Significantly different taxon Un--s-Fungi sp exhibited a positive correlation with total root: shoot ratio.The relative abundance of Glomeromycota and Blastocladiomycota were closely related with the total density and belowground biomass of grasses.In conclusion,different plant functional groups caused by grazing effected soil bacterial diversity significantly.Herbivore foraging aboveground part of plant effected soil bacterial biomass significantly.The driving forces of the changes of bacterial community mentioned above were soil physical and chemical changes.Moreover,the bacterial and fungal community composition changed in the both experiments.Conversely,the changes of bacterial and fungal individual groups resulted from soil nutrients and dominant grasses respectively.This study showed the distinct responses of soil bacteria and fungi to grazing.The study proved that plant community and the soil characteristics caused by live plant were critical pathway of herbivore effecting soil microbes.And it was helpful and important for understanding aboveground and belowground multitrophic interactions and forecasting the role of grazing in the grassland ecosystem.