Root microbiome changes with root branching order and root chemistry in peach rhizosphere soil

The plant root system influences plant growth and development due to its phenotypic, physiological, metabolomic, and microbiomic traits. Broadly speaking, it is characterized by primary (stem-attached large), secondary (primary-attached medium), and fine (secondary-attached hair-like) roots. The role of root branching order and categories (fine, medium, and large) in influencing microbial communities in the rhizosphere and root environments is not clear. We studied whether and how different root categories influence the composition of root and rhizosphere microbial communities in young peach trees. Using next-generation 16S rRNA amplicon sequencing (V3–V4 region), we profiled the microbial communities of roots and rhizosphere environments from phylum to species-level taxonomies. We demonstrated that different root categories showed a unique microbial community composition. Interestingly, fine or small roots recruited more diverse and species-rich microbial communities, very likely due to their better mineral contents (e.g., Mo, Fe, Mn, S, Zn, Cu, K, and P) and exposure with soil, though more research is needed to establish these relationships. Small roots and their rhizosphere environments showed a higher abundance of important bacterial taxa (e.g., Bradyrhizobium, Pseudomonas, Streptomyces, Burkholderia, Sphingomonas) that are previously known to play important roles in soil disease suppressiveness, plant growth, nutrient fixation, solubilization, and cycling. We suggest that linking microbial communities and their functions to root branching order and categories may enhance our understanding of rhizospheric interactions, soil disease suppressiveness, and their role in tree fruit performance.