Plant growth-promoting bacteria improve growth and nitrogen metabolism in maize and sorghum

Plant growth-promoting bacteria (PGPB) present potential to be used in agriculture supporting plant growth and improving physiological responses even in N-fertilized soils. Thus, this study aimed to evaluate PGPB inoculation, combined or not with N-fertilizer, on growth and N metabolism of maize and sorghum. A total of thirteen PGPB, with high variability in producing indole-3-acetic acid and nitrogenase activity were inoculated in maize and sorghum grown with and without N fertilization. The growth and physiological responses of plants were assessed 50 d after plant emergence. In general, PGPB increased maize and sorghum growth, N fixation efficiency and N metabolites as compared to non-inoculated plants. Particularly, IPACC55 and IPACC10 increased leaf area, chlorophyll, shoot dry mass, total N and symbiotic efficiency. The majority of PGPB increased the relative and N use efficiencies in maize. In addition, PGPB reduced free ammonia, while increased nitrate and soluble protein in maize and sorghum. The results also showed that inoculated maize and sorghum grown without N fertilization displayed higher plant biomass and relative and N use efficiencies, while that, in plants grown with N fertilization, the inoculation improved shoot dry mass, and symbiotic and N use efficiencies. As conclusion, PGPB positively influence N fixation and metabolism in maize and sorghum, even in N-fertilized soil. This indicates that PGPB can provide N to maize and sorghum and stimulate plant growth.