RHIZOSPHERIC BACTERIAL COMMUNITIES AND SEEDLING GROWTH OF Fraxinus uhdei Wenz. Lingelsh.

The application of plant growth-promoting rhizobacteria (PGPR) induces shifts in rhizospheric bacterial community composition. This study evaluated the effects of four Azospirillum brasilense strains in the rhizosphere of ash tree (Fraxinus uhdei Wenz. Lingelsh.) seedlings: two diazotrophic (nitrogen (N2) fixing) and two phosphate solubilizing strains. The analysis encompassed bacterial community structure, potential metabolic functions, and seedling growth and nutrition responses. DNA was extracted from rhizospheric soil, and the V3–V4 hypervariable region of the 16S rRNA gene was amplified and sequenced. The rhizobiome of A. brasilense inoculated plants was predominantly composed of seven phyla, with Proteobacteria being the most abundant (54 %). Alpha diversity analysis assessed by the Chao 1 richness and Shannon Weaver indices indicated that inoculation did not significantly alter species richness but resulted in a reduction of diversity. Inoculation with nitrogen-fixing (NF) strains led to a sevenfold increase in the relative abundance of the genus Azospirillum compared to uninoculated plants (Psi). Beta diversity analysis based on Bray-Curtis dissimilarity revealed a significant separation between the bacterial communities of inoculated and control plants. Prediction of metabolic potential via the Kyoto Encyclopedia of Genes and Genomes (KEGG) indicated that inoculation significantly altered (p ≤ 0.05) the relative abundance of 11 % of the predicted potential functional pathways. Analysis of variance (ANOVA) and the post-hoc Tukey test (p ≤ 0.05) demonstrated that co-inoculation with both strains yielded the most significant growth enhancements, with increases of 11.4 to 36.9 % across measured variables. FN strains increased macronutrient content by 15 to 24 %. These findings demonstrate that A. brasilense inoculation influences the structure and predicted functions of the rhizobacterial community and acts as an effective PGPR by enhancing the growth and nutrition of F. uhdei seedlings.