Effects of Plant-Growth-Promoting Rhizobacteria on Soil Bacterial Community, Soil Physicochemical Properties, and Soil Enzyme Activities in the Rhizosphere of Alfalfa under Field Conditions

Background: Inoculation with plant-growth-promoting rhizobacteria (PGPR) effectively increases plant growth in agriculture. However, the role of the rhizobiome in plant growth remains unclear. Methods: Biolog Ecoplate and 16S rRNA gene high-throughput sequencing techniques were used to analyze the changes in microbial community diversity, composition, and function after PGPR inoculation. Soil physicochemical and enzyme activities were also measured. Results: PGPR inoculation significantly promoted the growth of alfalfa. Using a Biolog Ecoplate, inoculation improved the metabolic activity and carbon source utilization of soil microorganisms. PGPR inoculation significantly increased the diversity and richness of the soil bacterial community in the rhizosphere of alfalfa and increased the relative abundance of key bacterial taxa such as Arthrobacter, Sphingomonas, and Bacillus, which are conducive to plant growth. Conclusions: Inoculation with PGPR enriched bacterial taxa and improved the utilization of carbon sources beneficial for plant growth. PGPR inoculation induced changes in microbial community diversity, and relevant functions in the rhizosphere contributed to alfalfa growth under field conditions.