Characteristics of rhizosphere and bulk soil microbial communities in pear trees.

Rhizosphere bacteria play a crucial role in promoting plant health and development. A full understanding of the bacterial communities in rhizosphere soil and their relationship with those in bulk soil is important for supporting plant growth. Some beneficial bacteria are recruited to the root-zone when plants experience different stresses. However, it is unknown whether the rhizosphere of pear trees enriches some beneficial microorganisms that can resist pathogen infections in natural ecosystems. In this study, we found a higher proportion of antagonistic strains in the rhizosphere of pear trees compared to bulk soil under natural growth conditions. By deep sequencing the V3 and V4 hypervariable regions of 16S rRNA genes, we characterized the bacterial communities in the rhizosphere soil of 'Yuluxiang' pear trees and the adjacent bulk soil. Our analysis revealed that the diversity of the bacterial community in the rhizosphere soil was lower than that in the bulk soil, but their compositions differed between the two soil types. We found that 12 phyla, 97 families and 130 genera contributed to these differences. Proteobacteria was the dominant phylum and its relative abundance in the rhizosphere soil was significantly higher than that in the bulk soil. Notably, the two genera, Bacillus and Pseudomonas, were more abundant in the rhizosphere soil. Compared with the bulk soil, the pear rhizosphere soil existed a higher proportion of beneficial bacteria with antagonistic activities against Fusarium oxysporum. These findings indicated that the pear tree rhizosphere can selectively assemble beneficial bacteria with specific antagonistic activities to address threats from pathogens. The distinct bacterial community structure in the rhizosphere of plants reflects a spontaneous ecological adaptation mechanism of plants to their environment.