Effects Of Grazing Intensities On Soil Microbial Community Diversity In Typical Steppe Of Inner Mongolia

Steppe ecosystem is the largest terrestrial ecosystem in China,while excessive grazing promotes grassland desertification.Soil microbial community diversity index is an important basis for evaluating soil fertility,which has been focused by ecological research.In this study,the typical steppe in Inner Mongolia was selected as the research object.Five grazing intensities were set,which were marked as CK,GI170,GI340,GI510 and GI680.The study used 16 S rDNA and ITS gene library techniques and Illumina Mi Seq sequencing technology to analysis the microbial community diversity.Faith's PD Index of microorganisms was calculated by R software.Structural equation model was used to analyze the causal relationship among grazing intensity,soil physicochemical properties and microbial community diversity.The conclusion we got as below:First,under the control treatment,the species richness of bacteria was the highest,and the quantity of bacteria was the lowest.With the increasing of the grazing pressure,the number of bacteria gradually increased and its species richness decreased.The Faith's PD index of bacteria was the smallest in the CK group,there was a maximum at GI170 and GI510,and there was no significant differences between the groups.Second,with the increase of the grazing pressure,the number of species,quantity and Shannon index of soil fungi showed a unimodal trend,and the maximum value appeared when the grazing pressure was GI340.This situation was consistent with Moderate Disturbance Theory.Moderate grazing contributes to the proliferation of fungi.Third,with the increase of grazing intensity,soil available nitrogen and water content gradually decreased;total soil organic carbon,total nitrogen,total phosphorus,and p H increased with the increase of grazing pressure and then decreased.The maximum grazing intensity appeared;the soil available phosphorus content decreased first and then increased with increasing grazing intensity,and was the lowest at GI510.Fourth,grazing significantly reduced the soil moisture content,resulting in changes in bacterial community structure and species diversity,which in turn affected the availability of soil available nitrogen and available phosphorus.Fifth,grazing affected some of the unknown factors,disrupted the structure and quantity of fungi,and changed the content of soil total nitrogen and available phosphorus.