| As the main constructive species of Inner Mongolia grassland,perennial xerophytic Stipa spp.has important ecological and economic value.From east to west of Inner Mongolia grassland,there is a regular distribution of interspecific geography and habitat substitution.Rhizosphere is a unique soil micro-ecological system different from non-rhizosphere areas and participates in the slow ecological process of vegetation succession.In this study,seven zonal Stipa species(S.baicalensis,S.grandis,S.krylovii,S.klemenzii,S.glareosa,S.gobica and S.breviflora are distributed from east to west)distributed from northeast to southwest of Inner Mongolia grassland were studied to reveal the regional scale variation of rhizosphere microbial diversity(including AM fungi),community assembly process and functional characteristics,and species synergistic distribution phenomena as well as driving factors during the geographic substitution distribution of Stipa species.The main results and conclusions are as follows:1)A total of 252 plant species belonging to 41 families and 140 genera were recorded in Inner Mongolia.Compositae,Leguminosae,Gramineae and Liliaceae are the dominant families of the seven types of Stipa grasslands,and the life forms(7species),water ecotypes(6 species)and floristic geographical elements(10distribution types and 19 subtypes)are rich,and there are significant differences and certain changes in different Stipa grasslands.There were significant differences in community diversity,quantitative characteristics,and most of the growth indicators and nutrients of Stipa spp.between different Stipa steppes and different Stipa species,and most of these indicators showed a decreasing trend from S.baicalensis to S.glareosa.In addition,during the alternative distribution of Stipa communities,the climatic geography and the rhizosphere soil characteristics of Stipa species were highly different.The soil nutrient content,water content,glomalin and dehydrogenase,urease,hydrolase and invertase activities tended to decrease from east to west,and most of the measurement indicators changed with the gradient of annual average precipitation and annual average temperature.2)The rhizosphere soil of Stipa is rich in microbial resources.Actinobacteria,Proteobacteria and Acidobacteria are dominant bacteria,and Ascomycota,Basidiomycota and Mortierellomycota are dominant fungi.The dominant bacterial phylum was an important contributor to the dominant functional groups predicted by the COG,KEGG and CAZy functional annotation libraries,and the contribution rate was significantly different among different Stipa species with the same function.In the process of Stipa transformation,some rhizosphere microbial taxa have a synergistic effect with Stipa species,and there may be an alternative distribution trend between several fungal classes,but no obvious microbial population substitution was found between different plots of the same Stipa species.3)Seven Stipa species established symbiotic relationship with AMF,and the mean annual temperature and soil fertility were the main positive and negative driving factors for AM colonization,respectively.The results of colonization rate and carbon contribution of GRSP showed that AMF had stronger carbon storage potential in barren environment.A total of 83 species of AMF belonging to 11 genera and 9families were identified by high-throughput sequencing,while 34 species of AMF belonging to 8 genera and 5 families were isolated and identified by morphology,and Glomus was the dominant genus.The community structure,taxa,number andαdiversity index of rhizosphere AMF all changed significantly among different Stipa species.Some AMF taxa only appeared in the rhizosphere of some Stipa species,but there was no obvious replacement of species taxa in the whole vegetation evolution process,including different geographical distribution positions of the same Stipa species.The changes of plant species,vegetation coverage and climate gradient promoted the differentiation of AMF community structure and quantity in the rhizosphere of different Stipa species,while the response of AM fungal groups(genera)to ecological environment factors was different.4)Co-occurrence network analysis showed that the relative importance of different Stipa plants to the construction of rhizosphere microbial symbiotic network was different,and the ecological importance of bacterial co-occurrence network(degree centrality,closeness coefficient and betweenness centrality)was greater.The correlation of Stipa rhizosphere microbial community is mainly positive correlation.The topological characteristics of S.breviflora rhizosphere microbial network are complex,with more close and clustered connection nodes,but the positive correlation connection is absolutely high,which is easy to have consistent feedback on environmental changes,so the network stability is poor,and the modularity and modularity of the network are the lowest.The rhizosphere microbial network of S.breviflora was more complex but less stable,and the modularity of the network was the lowest.S.krylovii rhizosphere bacterial network and S.grandis rhizosphere fungal network were simple and stable.Through the network zi-pi plots analysis found a series of key species(phylum and genus levels),and that low abundance groups and non-dominant bacteria may play an important role in maintaining the function of fungal network.5)At the regional scale,there was a significant separation of bacteria and fungi along the change direction of Stipa community,and Stipa taxa had a significant effect on the composition of rhizosphere microbial community(P<0.01),explaining 39%and 24.0% of the variation of bacterial and fungal composition,respectively.In the process of geographical distribution of Stipa species,the bacterial and fungal community structure in rhizosphere soil was significantly differentiated,which was mainly affected by climatic factors and Stipa species.In addition,phylogenetic and zero-model analysis showed that stochastic processes played a greater role in the formation of rhizosphere microbial community structure(including AM fungi)than deterministic processes,and diffusion limitation determined the succession trajectory of rhizosphere microorganisms(AM fungi)to a greater extent,especially in the fungal community.The relative role is greater,accompanied by a certain non-dominant process(drift or weak selection).6)Based on the prediction of metagenomic sequencing,46 sub-functional groups from 6 metabolic pathways were found in the rhizosphere microbial gene sequence of seven Stipa species.The metabolic pathways at the KEGG level 3 level,biosynthesis of metabolic pathways,biosynthesis of secondary metabolites,microbial metabolism in diverse environments and carbon metabolism were the main metabolic functional groups.CAZymes analysis showed that glycoside hydrolases and glycosyl transferases were the most representative carbohydrate enzymes.The distribution of microbial function was significantly differentiated with the succession of Stipa,and the composition of microbial functional groups between Stipa species distributed in desert steppe,and between Stipa species distributed in meadow steppe and typical steppe was more similar.In addition,the functional categories predicted by egg NOG and KEGG databases had little changes between the rhizosphere of seven Stipa species and had no obvious change rule,while glycoside hydrolase and glycosyltransferase may have a certain complementary effect with the geographical substitution of Stipa species.This study makes full use of the advantages of multidisciplinary,multi-omics sequencing and multivariate statistical analysis methods to comprehensively reveal the changes and driving factors of the assembly and functional characteristics of the rhizosphere microbial(AMF)community during the geographical substitution distribution of seven Stipa species.It lays a theoretical foundation for analyzing the interaction between plants and rhizosphere soil microbial communities in grassland ecosystems and the strategies and mechanisms of synergistic ecological adaptation. |
PDF Full Text Request