Bacillus subtilis changes the root architecture of soybean grown on nutrient-poor substrate

Abstract

The potential of Bacillus subtilis in promoting soybean growth under conditions of low availability of nutrients was assessed in a pot experiment. The experiment was carried out in a completely randomized design with five treatments, as follow: (T1) Bradyrhizobium japonicum; (T2) B. japonicum + non-inoculated organic fertilizer; (T3) B. japonicum + inoculated organic fertilizer; (T4) B. japonicum + B. subtilis; and (T5) B. japonicum + NPK. All inoculated treatments were applied directly to the soybean seeds. Soybean was grown in a controlled growth chamber and, on the 40th day, plants were collected and evaluated. B. subtilis increased root dry weight, root:shoot ratio, number of nodules, and specific nodulation, while chemical fertilization increased the shoot biomass and leaf area. The presence of B. subtilis in the substrate was confirmed by the highest number of colonies found in the inoculated treatment. B. subtilis contributed to higher chlorophyll content and it was similar to treatment with chemical fertilization. The roots length, surface, and volume increased with the chemical fertilization and with B. subtilis. Also, B. subtilis modified the partitioning of assimilates in soybean with an increase in root biomass and changes in root architecture due to the increase in the surface of intermediate roots. This study reinforces that co-inoculation of soybean with Bradyrhizobium and B. subtilis is an efficient strategy to improve plant growth due to their beneficial effects in root architecture, which can contribute to higher uptake of water and nutrients.