Comparative effects of conventional rhizobial inoculants and novel PGPR consortia on rhizosphere microbial parameters and soybean performance

Abstract

Bradyrhizobium-based inoculants are widely used in soybean production. Under the field conditions, numerous abiotic and biotic factors can compromise strain survival and significantly reduce their effectiveness. The application of PGPR consortia represents a promising approach for improving the quality of conventional inoculants and soybean performance while supporting beneficial microorganisms in the rhizosphere. This study aimed to comparatively examine the effects of three bacterial treatments: Bradyrhizobium japonicum consortium alone and in combination with two distinct PGPR consortia, which differ in strain composition and origin. The inoculants were evaluated on sterile chernozem soil in a pot experiment under semi-controlled conditions by assessing soybean growth, biomass, and nodulation, as well as rhizosphere microbial abundance and activity. The conventional rhizobial inoculant supplemented with a drought-adapted PGPR consortium originating from the soybean rhizosphere significantly increased the abundance of total bacteria, free-living nitrogen-fixing bacteria, azotobacters, and ammonifiers, as well as dehydrogenase activity and soil respiration, compared with Bradyrhizobium inoculation alone or in combination with the other PGPR consortium. The greatest effect on soybean growth and biomass was also observed with this bacterial treatment, indicating the potential of novel PGPR strains to improve the quality and effectiveness of conventional inoculants. The obtained findings could contribute to the development of more effective soybean inoculation strategies through the selection of functionally diverse but complementary bacterial strains adapted to the host plant and specific environmental conditions.