Differences in metabolism and composition of microbial communities in rhizosphere soils with different deciduous fruit trees

Abstract:【Objective】Rhizosphere effect driven by plant root exudates can affect the rhizosphere environment, including changes in soil pH, soil physical and chemical characteristics, and microbial communities. As the second genome of plants, rhizospheric microbial community plays a vital role in plant growth, and its composition and metabolism determine the intensity and direction of the rhizospheric nutrient cycle. The main ways for microbe to promote nutrient uptake by plants are mineralization of organic matter and activation of effective states of mineral elements, which can significantly affect fruit yield and quality. However, little is known about the differences between rhizospheric microbial com- munities in different fruit trees, especially in deciduous fruit trees. Therefore, it is necessary to study the composition and metabolism of the soil microbial communities, and to explore the differences of micro- bial communities in the rhizospheres of different fruit trees【. Methods】The experienment was conducted at Xinxiang Integrated Test Base, Zhengzhou Fruit Research Institute, Chinese Academy of Agricul- tural Sciences, located in Henan province of China. Eight deciduous fruit trees including apple, pear, apricot, cherry, peach, grape, walnut, and pomegranat, were planted in March 2012. The plots without fruit trees were used as controls (CK). Soil samples were collected from 10-20 cm soil layer in the rhizo- spheres of eight deciduous fruit trees in May 2017, placed in a sterile bag, and stored at −80 °C. The Bi- olog EcoPlate method and Illumina Miseq sequencing technology were used to measure the metabolism and composition of different fruit trees rhizospheric microbial communities【. Results】The metabolic ac- tivity and functional diversity indexes (except Pielou index E) of the microbial communities in the eight fruit trees rhizosphere were significantly higher than those of the CK. The rhizospheric microbial com- munities of apple, grape, pomegranate and cherry had higher metabolism, while peach, pear and apricot tree had lower metabolism; the E index of peach was higher than those of the others, and the functional diversity indexes (Simpson D, Shannon-Wiener H, McIntosh U and S) of microbial community func- tion of pomegranate, cherry and apple rhizosphere were higher than those of the others. The characteris- tics of carbon source utilization showed that the utilization ratio of phenolic compounds (PC) of the apricot rhizospheric microbial community decreased significantly, while the utilization ratio of carbohy- drate (CH) significantly increased. And the soil microbial community of CK had the highest percentage of amino acids (AA) carbon source utilization. In addition, the percentage of CK’s utilization of amino acid was significantly higher than those of the fruit trees. The relative abundances of bacterial and fun- gal communities at the level of the genus varied with 8 fruit trees rhizospheres; the relative abundance of γ-proteobacteria of apple and walnut were significantly higher than those of the other fruit trees. In addition, compared with the bacterial communities, the fungal communities in the rhizosphere of the eight fruit trees were more significantly different. Differences in the bacterial community levels at the family level showed that the relative abundance of Blastocatellaceae in the rhizosphere of apricot trees was significantly higher than those of the other fruit trees (except pomegranate), the lowest was found in apple. The Gemmatimonadaceae relative abundance of the peach trees was significantly higher than those of other fruit trees, and the lowest was found in the pomegranate trees. The relative abundance of Agariceae in walnut rhizosphere was significantly higher than those of the other tree species, while the lowest was found in pomegranate rhizosphere. The relative abundance of Mortierellacea in apricot and pomegranate rhizospheric soils was relatively higher than those of walnut, cherry, peach and apple. The relative abundance of Nectriaceae and Pleosporaceae in the control sample was significantly higher than those of the rhizospheres of the eight deciduous fruit trees. Correlation analysis between the predominant bacteria at the class level and microbial community metabolism revealed that Betaproteobacteria, Alphaproteobacteria, and Sphingobacteriia were significantly positively related to the microbial community metabolism, while Gemmatimonadetes, Sordariomycetes, Glomeromycetes, and Chytridiomycetes were significantly negatively related to the microbial community metabolism. In addition, RDA analy- sis showed that the microbial functional diversity (except E) was positively correlated with the bacterial alpha diversity and negatively correlated with the fungal alpha diversity【. Conclusion】There were signif- icant differences in the metabolism and functional diversity of the microbial communities of the eight northern deciduous fruit trees. Also, there were significant differences between the bacterial and fungal communities in the rhizospheres of the eight fruit trees, while the differences of the fungal communities were more significant than those of the bacterial communities. The rhizosphere microbial community metabolism was positively correlated with the bacterial community and negatively correlated with the fungal community.