Effect of auxin producing and phosphate solubilizing bacteria on mobility of soil phosphorus, growth rate, and P acquisition by wheat plants

Microorganisms capable of mobilizing phosphate promote plant growth, this activity being frequently accompanied by production of plant hormones auxins. However, the extent of contribution of these characteristics to promotion of plant growth remains unclear. Paenibacillus illinoisensis IB 1087 and Pseudomonas extremaustralis IB-Ki-13-1A strains were selected for their capacity to mobilize phosphates and to synthesize auxins in vitro. The effects of inoculating these bacteria on the content of mobile phosphorus in the soil as well as on the phosphorus and hormone content in wheat plants were studied and the observed responses were related to the changes in plant growth. Inoculation of bacteria into the soil increased P concentration in the plants suggesting their increased capacity for the efficient acquisition of phosphorus compounds, while concentration of mobile phosphorus in the soil was increased by its inoculation with bacteria only in the absence of plants. The treatment increased plants mass (to greater extent in the case of P. illinoisensis) in accordance with the increased level of auxins in the treated plant. Increased mass accumulation did not correlate with the potential ability of bacteria strains for production of auxins or phosphate mobilization in vitro. Our data indicate importance of increased auxin content in the plants for the stimulation of root growth and capacity for P uptake as influenced by growth-promoting bacteria.