| The maintenance mechanism of community structure and diversity is one of the core issues in ecological research.Microorganisms are the main drivers of biogeochemical cycles and play an important role in maintaining the structure and function of ecosystems.In recent years,the distribution pattern and biodiversity maintenance mechanism of microbial community have attracted much attention.Applying niche theory and neutral theory to explain the construction mechanism of microbial community is the mainstream view of community ecology at present.The former emphasizes the importance of deterministic processes,while the latter emphasizes the importance of stochastic processes.However,due to the differences in research scale,species attributes,and habitat conditions,the relative role of the two in the community construction process is a hot topic in current ecological research,especially in the field of microbial ecology.Shanxi province is located in the east of the loess plateau.The complex topography,diverse climate and soil conditions provide good conditions for the development and survival of species.The subalpine zone in this region has the cold climate,abundant precipitation,and large diurnal temperature difference and sunshine intensity.In addition,the large span of mountain elevation can show a large climatic gradient and latitude gradient within a relatively short geographical distance,making it an ideal experimental site to study the community construction process and the maintenance mechanism of biodiversity.The study samples were collected from the concentrated distribution areas of larch forests in north China(Wutai mountain,Guandi mountain Pangquangou nature reserve and Luya mountain)in Shanxi province.Moreover,single vegetation type can reduce the disturbance of unknown environmental factors.Using high-throughput sequencing methods on soil microbial community structure and diversity of structure,drive factor to conduct research,andbased on the different biological properties(bacteria,fungi,habitat groups of generalization and specialization,cbb M functional groups)and different habitat conditions(shady slope and sunny slope,different research site)and multiple dimensions,and further reveals the environmental heterogeneity of ecological community structure and function mechanism,the influence of the process of building a clear subalpine coniferous forest soil microbial community to determine the relative importance of process and the stochastic process,for the community diversity maintaining mechanism to provide more theoretical basis.The main research contents are as follows:1.The bacterial and fungal community structure,composition and diversity patternsBacterial and fungal communities had different structure,composition and diversity patterns in different research sites.The relative abundance of Proteobacteria,Acidobacteria and Actinomycetes were higher in the bacterial community.In the fungal community,the relative abundance of Ascomycota,Basidiomycota and Zygomycota were higher.In bacterial and fungal communities,the key species(common species,differential species,and important species)varied widely in different habitats.Through network analysis,both bacterial and fungal communities showed non-random co-existence patterns.The distribution of bacterial and fungal communities showed a distinct nesting pattern and a distinct separation trends.2.Driving forces of bacterial and fungal community assembly processesBoth bacterial and fungal communities were driven by deterministic and stochastic processes,but deterministic processes dominated.Compared with the bacterial community,the assembly processes of the fungal community were more influenced by the determination processes.(1)For the bacterial community,soil p H,SOC and TN had significant effects on the structure of soil bacterial community,and SOC had the greatest impact on the diversity of bacterial community.Therefore,it wasconcluded that SOC was the most important soil physicochemical factor affecting the bacterial community.(2)For the fungal community,soil p H,SOC,TC and TN had significant effects on the structure of the soil fungal community.Basidiomycetes were mainly affected by p H and SOC,and p H had the greatest effect on the diversity of in the fungal community.Therefore,it was concluded that soil p H was the most important soil physicochemical factor affecting the fungal community.3.Discuss the composition structure and diversity pattern of microbial groups from different biological attributes,habitat conditions.(1)Different ecological groups(habitat generalization,specialization and transition groups)had different optimal ecological niches and degree of niche differentiation due to different degree of response to environmental heterogeneity,showing different community structure and composition.Proteobacteria had the highest relative abundance in the three ecological groups,followed by Chlorobacteria and Bacteroidetes.No Acidobacteria were found in the habitat generalization groups.The logarithmic series model was more fitted to habitat specialized groups,while the logarithmic normal model was more fitted to habitat generalized groups and transition groups.(2)The species richness and diversity index of the bacterial community in the shade slope were higher than those in the shade slope for the microbial communities in different habitat conditions(shade slope and sunny slope).The similarity of bacterial communities between different plots were small.A total of 43 bacterial phyla were identified in all plots.According to the Venn diagram,there were 644 OTUs bacteria Shared between the shady slope and the sunny slope.The relative abundance of proteobacteria was the highest in all the plots.(3)For cbb M functional groups,most of the carbon sequestering microbial groups were unidentified.Among the identified groups,therelative abundance of Proteobacteria was the highest,followed by Actinomycetes and Bacteroidetes.Venn diagram showed that the total number of OTUs shared by each sample site was 91,with E2200 having the most unique OTUs.And the community diversity of E2200 was higher.4.Explore the driving factors for the construction of microbial communities from different biological attributes,habitat conditions and other dimensions(1)For ecological groups,according to distance-based RDA analysis(db-RDA),environmental factors had a significant impact on the microbial community.Moreover,the results of the stepwise model showed that SOC was the most important factor,followed by TN and p H.Through multiple regression tree analysis,SOC had the greatest direct effect on species diversity.Therefore,SOC was the most important factor affecting different ecological groups in the study area.Moreover,the community assembly process was mainly driven by the deterministic processes.(2)Based on different habitat conditions,namely,different slope directions(negative slope and positive slope)or different habitat conditions(WT,PQG and LY site),the deterministic processes,especially environmental filtration,drove the construction process of microbial community in this study.On different slopes,soil physicochemical factors had the greatest influence on bacterial community structure,followed by vegetation diversity and spatial variables.In soil physical and chemical factors,total carbon and total nitrogen were the most important influencing factors.Elusimicrobia and Cyanobacteria were mainly affected by TC and TN.The Bacteroidetes and Proteobacteria were mainly affected by ammonium nitrogen content(3)The assembly process of cbb M carbon sequestering microflora was mainly driven by environmental filtration(deterministic processes).The above-ground vegetation diversity had more influence on it thansoil environmental factors.Among them,Proteobacteria and Bacteroidetes were mainly affected by conductivity and TC.The community Calditrichaeota was mainly affected by salinity.5.Response mechanism of microbial community function to environmental heterogeneity(1)The results of QPCR showed that there were significant differences in the copy number of functional genes of cbb M,cellulase and amylase in different research sites,indicating the differences in carbon fixation and carbon metabolism functions in different research sites.Moreover,the microbial community of WT had great potential for carbon sequestration and ability to decompose refractory carbon.The process of carbon sequestration was dominant in soil,and the decomposition of easily decomposed carbon was dominant.The microbial community functions were significantly different in different slope directions,but the community structure was not significantly,which indicated that the microbial community function was more sensitive to environmental heterogeneity than the community structure.(2)Biolog Eco plate experiment showed that WT site had higher carbon source utilization capacity(AWCD value was higher)and higher carbon metabolism diversity.The metabolism of amino acids,lipids,alcohols,amines and acids at the WT site were greater than that at the other two sites,while there was no significant difference in the metabolism of monosaccharides.(3)Different ecological groups mediate different community functions,and most community functions were mainly performed by transitional groups.These metabolic functions mainly included aerobic ammonia oxidation,aerobic heterotrophic oxygen nitrite oxidation,chemotrophicnitrification,nitrate respiration,aerobic photoautotrophic,photoautotrophic;photosynthesis.A few community functions were performed mainly by habitat generalization groups.They mainly includemethane oxidation and methyl nutrition.However,the specialists groups perform only one major community function: nitrate respiration.(4)By FAPROTAX,the function prediction of the bacterial community showed that the highest metabolic activity was chemohetero;the next were aerobic chemoheterotrophic,nitrification,aerobic nitrite oxidation,and aerobic ammoxidation.(5)Through FUNGuild,the nutrient types of the fungal community were exogenous mycorrhiza,plant pathogens,animal pathogens.To sum up,the deterministic process and stochastic processes in this study area jointly drove the assembly processes of microbial community.The relative importance of the two was closely related to biological attributes and habitat conditions,but the deterministic process always prevailed.Microbial community structure and community function showed a synergistic response to environmental heterogeneity,but community function was more responsive to environmental heterogeneity. |
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