Effects Of Grazing On The Composition And Diversity Of The Endophytic Microbial Community In Leymus Chinensis In Songnen Grassland

The interaction between plant and microbe is a hot topic in plant ecology field.Studies have shown that the diversity of endophytes in rhizosphere soil and different tissues are crucial to plant growth and development.Grazing is one of the main strategies for grassland management and utilization.It can regulate the structure,function and stability of grassland ecosystem through affect the aboveground plant community construction and underground biogeochemical cycle via feeding forage,trampling,feces and urine.Leymus chinensis is an important dominant species of grassland in northern China.It has good palatability,high yield and high feed value,and thereafter is important for economy and ecology.As a complex microecological system,L.chinensis contains a large number of endophytic bacteria and fungi.However,the community structure and diversity of endophytes in different growth periods and different tissues of L.chinensis and their response to grazing remain unclear.In this study,the community composition of endophytic bacteria and fungi in the rhizosphere soil and different tissues（roots,stems,leaves）of L.chinensis were studied.The changes of species,quantity and abundance of endophytic bacteria and fungi in different compartments of L.chinensis with different growth periods were compared using high-throughput sequencing method.The spatial and temporal niche differences of endophytic bacterial and fungal community composition and diversity were determined as well.The relationship between grazing related environmental factors and the community structure and diversity of endophytes was analyzed.The pathway of grazing affecting the spatial and temporal niche differences of endophytes of L.chinensis was clarified.Finally,the influence and mechanism of grazing on the community composition and diversity of endophytic bacteria in L.chinensis were revealed.The main research conclusions obtained are as follows:（1）There were spatial niche differences in community composition and diversity of endophytes in L.chinensis.The richness and diversity of endophytic bacteria and fungi in different tissues of plants decreased in order of roots>stems>leaves,Cyanobacteria、Proteobacteria、Actinobacteriota、Chloroflexi colonized widely in plant tissues,but the abundance was different.The composition of fungal communities in each tissue was different,but among them,Pleosporales are dominant fungi in each tissue.（2）There were time niche differences in the composition of the endophytic community of L.chinensis.The community composition of endophytic bacteria and fungi in plant seedling and mature stage was different,but Alphaproteobacteria and Actinobacteria were dominant bacteria,while Sordariomycetes and Dothideomycetes were dominant fungi.Furthermore,the network complexity of endophytic bacteria and fungi communities in seedling stage was higher than that in mature stage.（3）Grazing shaped the spatial and temporal niche differences of the community structure and diversity of endophytes.Grazing increased the relative abundance of bacteria and fungi in different tissues of plants at seedling stage,including Cyanobacteria and Pleosporales、unclassified＿p＿Basidiomycota and Capnodiales in rhizosphere soil,Filobasidiales and Tremellales in roots.Moreover,grazing increased the relative abundance of bacteria and fungi in different tissues of mature plants,including the Firmicutes in roots,Chloroflexi、Gemmatimonadota、Nitrospirota、unclassified＿c＿Sordariomycetes and Pezizales in leaves,and the Capnodiales、Sordariales in stems.The diversity of fungi and bacteria in stems and bacteria in roots of grazing grassland was lower than that of non-grazing grassland（Shannon index）.The diversity of bacteria in rhizosphere soil and fungi in leaves of mature plants in grazing grassland was lower than that of non-grazing grassland,while the diversity of bacteria in leaves was higher than that of non-grazing grassland（Shannon index）.There are common bacteria in plants of seedling stage and mature stage in grazing grassland,but the dominant taxa are different.In seedling stage,the dominant bacteria and fungi were Cyanobacteria and Pleosporales,respectively;while in mature stage,the dominant bacteria and fungi were Actinobacteria and Hypocreales,Pleosporales,respectively.（4）Grazing changed soil properties and plant traits.Grazing significantly reduced the soil total carbon,total nitrogen and total phosphorus,but significantly increased the soil nitrate nitrogen,ammonium nitrogen and sodium ion.The soil p H and electrical conductivity of grazing grassland were higher compared with non-grazing grassland.The concentrations of C and N or N and P in the roots,stems and leaves of L.chinensis at seedling stage or mature stage in grazing grassland were both significantly higher than that in non-grazing grassland.The results of redundancy analysis（RDA）and Mantel test showed that the endophytic bacterial community of L.chinensis at seedling stage was significantly correlated with the concentrations of plant nutrients（C and N）,cations（Na⁺,K⁺）and anions(Cl^-and SO₄^2-),while the endophytic fungal community was strongly correlated with the concentrations of plant nutrients and anions.However,the endophytic bacteria community of L.chinensis at mature stage had significant correlation with the concentrations of plant cations(Na⁺,K⁺,Ca²⁺)and anions,while the endophytic fungi community was strongly correlated with the concentrations of plant nutrients（N and P）and anions.In conclusion,the results revealed that grazing affected the time and spatial niche differences of endophytic bacteria and fungi community composition and diversity by influencing soil available nitrogen（nitrate nitrogen and ammonium nitrogen）,and the distribution of nutrient and ion between plant tissues.The current study has important theoretical significance for understanding the endophyte species of L.chinensis and the coevolution relationship between plant and endophytes.It is helpful to reveal the regulation of human activities（grazing）on plant-microbe interaction in grassland ecosystem.It is of great significance to clarify the growth adaptability mechanism of L.chinensis and formulate more reasonable grazing management mode.