| Elm open woodland is the most important ecological unit and the most stable and adaptive community in the Otindag Sandy Land.Ulmus pumila var.sabulosa is the construction species of the elm open woodland.Its cold and drought resistance makes it play an important role in maintaining biodiversity,vegetation restoration,wind prevention and sand fixation.The rhizosphere is the link between plant root system and soil environment,with the most frequent microbial activities in this area.In this paper,high-throughput sequencing technology was used to study the bacterial and fungal communities of the elm rhizospheric soil.It revealed the spatial and temporal distribution patterns of the elm rhizospheric microbe,illustrated the forming mechanism and driving factors of their distribution patterns,predicted the function of rhizospheric microorganisms,filled in the blank in the research of elm rhizospheric microbes,and laid a theoretical foundation for subsequent study on the relationship between root of this tree and soil microbialinteractions.Findings of this study are in the following:(1)Spatial and temporal distribution of the soil physical and chemical properties and enzyme activities in the rhizosphere soil of elm were observed.The pH range of rhizosphere soil in different areas was 7.30?7.80,and the moisture content was 2.71%?3.41%.The soil spatial heterogeneity of physical and chemical properties and enzyme activities in rhizosphere was mainly reflected in pH,available phosphorus content and available potassium content.The physicochemical properties and enzyme activities of the rhizosphere soil of elm showed different responses to the microtopography,which was manifested by the law that the soil moisture,nutrient conditions and enzyme activities in the dune-lowland soil were significantly higher than those in the leeward slope and the windward slope(p<0.05).The seasonal changes mainly caused the changes of soil moisture content and soil temperature in the elm rhizosphere,but had no significant effect on soil nutrients and soil enzyme activities.The soil nutrients content in the elm rhizosphere was closely related to the enzyme activity.(2)The rhizosphere soil of elm is rich in microbial resources.The 16S rRNA gene sequencing was annotated with a total of 11,738 bacterial OTUs(Operational Taxonomic Units)from 46 phlya,118 classes,167 orders,349 families and 675 genera,Proteobacteria,Actinobacteria and Thaumarchaeota were dominant bacterial phyla,and sum of average relative abundance was 58.53%.Pseudarthrobacter,Sphingomonas and Pseudonocardia were dominant bacterial genera,and the average relative abundance were 2.76%,1.82%,and 1.10%.The ITS region sequencing was annotated with a total of 7,787 fungal OTUs from 6 phyla,32 classes,118 orders,295 families and 655 genera.Ascomycota was the dominant fungal phylum in the rhizospheric fungal communities,and average relative abundance was 83.35%.Gibberella,Beauveria and Mortierella were dominant fungal genera,and the average relative abundance were 6.6%,2.77%,and 2.74%.The spatial distribution pattern of the microorganisms in the elm rhizosphere of was consistent with the zonal distribution pattern of the elm open woodland community,that was,there were significant differences among the community structures in different regions(p<0.05),and the similarity of community composition decreased gradually from west to east.(3)The existing spatial distribution pattern of elm rhizosphere microorganism was determined by diffusion restriction and environmental selection.Geographical distance contributes 6.38%and 4.02%to the formation of the rhizosphere bacterial and fungal community,and environmental factors contribute 62.7%and 67.09%to the bacterial and fungal community.Among environmental factors,pH,annual precipitation and species diversity of above-ground vegetation were the key factors driving the spatial distribution pattern of microbial communities.(4)The response of rhizosphere soil microbial species diversity to dune microtopography showe that species richness in lowlands and leeward slopes was greater than that in windward slopes.The bacterial and fungal communities in the eastern part of the sandy land had the most obvious response to the microtopography,where significant differences in the bacterial and fungal community structure between the lowlands and leeward slopes and windward slopes was formed(p<0.05).The small scale spatial distribution pattern of microorganisms in elm rhizosphere was the result of the synergistic effect of soil and vegetation.(5)Soil microorganisms showed a certain dynamic distribution with the seasonal changes.The diversity of rhizosphere microbial(bacterial and fungal)species of elm in spring and summer was significantly higher than that in autumn(p<0.05).Seasonal changes had less effect on the composition of the fungal community than bacterial community.There were significant differences in the structure of the rhizosphere bacterial community of elm ulm in the sandy land between different seasons(p<0.05).Seasonal changes in soil nutrients,water content and temperature were the key factors driving the seasonal distribution of rhizosphere soil microbial communities.(6)41 subfunctional groups from 6 metabolic pathways were determined in the elm rhizospheric bacterial gene sequences.Among these functions,membrane transport,amino acid metabolism and carbohydrate metabolism were the main metabolic function groups in the bacterial communities.There were significant differences in the spatial and temporal distribution of the functional groups of rhizospheric bacteria.The functional groups of bacteria in the west had more differences from the central and eastern parts of the sandy land,and there had great differences between summer and spring-autumn.Elm rhizosphere bacteria from different regions divides to 25 ecological function groups,and heterotrophic function,nitrate reduction and nitrification were the dominant ecological functional groups in the bacterial communities.The ecological functions of rhizospheric bacteria were spatially and temporally distributed,and their distribution patterns were consistent with the metabolic functions of bacterial communities.According to the ecological function,the elm rhizosphere fungal communities could be divided into 9 ecological function groups,among which saprotroph,pathotroph and symbiotroph were the dominant functional groups in the rhizospheric funal communities.The spatial distribution of fungal ecological function was significantly different(p<0.05),but the seasonal changes had no significant effect on the ecological function of fungal communities. |
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