| In this study,16 S r DNA high throughput sequencing(Illumina Mi Seq)technique,Real-time PCR and high performance liquid chromatography(HPLC)were used to analyze the soil microbial community structure,the relative abundance of nitrogen cycling functional genes and fungal biomass.Taking the rhizosphere soil of Rhododendron aureum Georgi in the tundra of the northern slope of Changbai Mountain as the main research object,analyzed the rhizosphere soil microbial community structure of different altitudes of R.aureum,different plant species at the same altitude and the different plant communities.The result shows:(1)different altitudes of R.aureum rhizosphere soil properties were significantly different.The elevation of 2600 m soil total nitrogen(TN)and total organic carbon(TOC)was significantly lower than that of other altitude;The activity of acid phosphatase in the rhizosphere soil(?2300m)was significantly higher than that in the low altitude(<2300).There was significant difference in fungal biomass at different altitudes,but no significant correlation with altitude gradient.There were significant differences in the relative abundance of carbon and nitrogen cycling genes in the rhizosphere soil of R.aureum with different elevation.The results of cluster analysis showed that high altitude(>2400m)of R.aureum rhizosphere soil microbial community structure similarity,and compared with the low altitude was difference.(2)Different vegetation rhizosphere soil at the same altitude of soil physical and chemical properties,fungal biomass and carbon and nitrogen cycling genes relative abundance were differed significantly.At 2200m~2600m,the total organic carbon content of R.aureum rhizosphere soil was significantly higher than that of other vegetation treatments at the same altitude.At the same time,compared with other plants,R.aureum rhizosphere soil has higher nutrient cycling function microbial and fungal biomass.The above results showed that R.aureum could improve the rhizosphere soil of tundra.The results of correlation analysis showed that the p H value was significantly correlated with the relative abundance of carbon and nitrogen cycling genes(except AOA);fungal biomass was significantly positively correlated with soil total organic carbon,total nitrogen,and microbial biomass C and sucrose activity.Species relative abundance and Heatmap analysis results showed that,at 2600 m different plant rhizosphere soil microbial community structure was similar,but there were differences in different rhizosphere soil microbial community composition at other altitudes.Among 2300m~2500,the microbial community composition of R.aureum rhizosphere soil was not gathered other two plants together at the same altitude.Through the determination of the rhizosphere soil of R.aureum mixed with different plant species,R.aureum and herbs mixed(Da+H)in the rhizosphere soil total organic content was significantly lower than that of R.aureum independent community(Da)and mixed with woody plant communities(Da+S),other soil nutrient content among different treatments was not significantly different.The relative abundance of fungal biomass,nitrogen fixation and carbon function genes abundance in mixed rhizosphere soil was significantly lower than that in Da.OTU richness analysis showed that the species diversity of mixed rhizosphere soil was significantly lower than that of the R.aureum independent community(Da).The results of NMDS showed that there were no significant differences in the microbial community structure of rhizosphere soil in different R.aureum plant communities.RDA analysis showed that fungal biomass and vegetation coverage could significantly affect the microbial community composition in rhizosphere soil.(3)Using the structural equation model(SEM)to analyze the interact on different factors the soil microorganism,the result found that vegetation cover degree(? = 0.504,P =0.004)and soil organic carbon(? = 0.51,P = 0.002)is the most direct control factors on rhizosphere fungi biomass;Soil p H is the main direct effect on rhiosphere soil microbial diversity(? =-0.551,P = 0.008)and community(? = 0.850,P < 0.001)factors;but consider the total effect on rhizosphere soil microbial,altitude was the strongest total effect(? = 0.603)on soil microbial community structure in rhizosphere,mainly through influence soil p H and TOC indirect effects rhizosphere soil microbial community.Taking the encroaching of Deyeuxia angustifolia as the main research object in in the tundra of the west slope of Changbai Mountain,analyzed the effects of encroaching on soil microbes in tundra.The results showed(1)The soil physical and chemical properties in the encroaching area of west slope of Changbai Mountain were significantly different,but the variation range of different in the two encroaching sites.The increase of total organic carbon and total nitrogen in the rhizosphere soil was significantly increased by the invasion of the woody plant communities,but there was no significant change in the herbaceous plant communities.The increasing rate of available nutrients in the herbaceous rhizosphere soil was higher than that of woody plants.Species difference analysis and NMDS results showed that the encroaching woody site rhizosphere soil microbial community structure were significant different,and a total of 4 bacteria phyla and 18 bacterial genus relative abundance were significantly difference.However,there was no significant difference in the microbial community structure of rhizosphere soil before and after the encroaching in herbaceous,and there were only 2 bacterial genuses relative abundance were significantly difference.(2)Analysis of microbial richness differences found that in D.angustifolia(DA)rhizosphere soil nitrogen fixing microbial richness was significantly higher than that in the tundra woody plant community(NS),and in the encroaching sites,the rhizosphere soil nitrogen fixing microbial richness was significantly higher than before D.angustifolia encroaching;and the rhizosphere soil microbial community structure was different significantly between native sites and D.angustifolia site,but there was no significant different in encroaching sites compared to D.angustifolia site.(3)The results of the investigation of plant communities showed that D.angustifolia encroaching could reduce the species diversity and aboveground biomass.D.angustifolia encroaching could significantly increase litter thickness;correlation analysis showed that between the change rate of total organic carbon and litter thickness was significant positive correlation. |
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