Abstract:[Background] The amount of phosphorus available for direct absorption and utilization by plants in the soil is limited, and the traditional methods of applying phosphorus fertilizer can lead to environmental pollution and problems such as damage to soil structure and function. [Objective] This study aimed to investigate the salt tolerance and phosphorus solubilization mechanism of Bacillus megaterium and Providencia rettgeri and their effects on soybean seed germination, to lay a solid foundation for inoculation and colonization of plant rhizosphere in saline-alkali soil. The problem of phosphorus deficiency in crops is expected to be solved through the phosphorus-solubilization effect of phosphorus-solubilizing bacteria in rhizosphere soil. [Methods] The inoculation with needlepoint, plate method, liquid culture method, and box germination experiment were conducted to analyze the salt-alkali tolerance, phosphorus-solubilization effect, and promotion effect on soybean germination of two phosphorus-solubilizing bacteria strains. [Results] Both B. megaterium and P. rettgeri could grow in environments with salt concentrations ranging from 0−10% and 0−6%, and pH values ranging from 7.0 to 12.0. The D/d values of B. megaterium and P. rettgeri on plates reached 2.17 and 2.05, respectively. The value of dissolved phosphorus in the liquid medium reached a peak on the 4th day, which were 355.53 and 272.17 mg/L, respectively, and the pH value of the culture medium decreased from 7.5 to 4.61 and 4.81, respectively. The phosphorus solubilization effect of B. megaterium and P. rettgeri showed a trend of “slightly increasing at first and then continuously decreasing” with the increase of NaCl concentration, and the pH value showed a trend of “slightly decreasing at first and then continuously increasing”. The best phosphorus solubilization effects were observed at NaCl concentrations of 0.4 and 0.2 mol/L, respectively, with the peak solubilization value of 364.35 and 285.58 mg/L, and the pH value of the culture medium decreased to the minimum value of 4.28 and 4.73, respectively. B. megaterium and P. rettgeri both increased the germination rate of seeds and elongation of the embryonic axis and radicle. Compared with the control group, in normal environments, the average germination rate, and the embryonic axis and radicle elongation rate of soybeans after soaking in the two bacterial solutions were 2.70%, 10.10% and 9.00%; in NaCl-treated environments, the corresponding value were 5.40%, 19.40% and 20.30%. [Conclusion] Both strains have strong salt tolerance and phosphorus solubilization effect and can promote seed germination, providing a theoretical basis for the inoculation and application of phosphorus-solubilizing bacteria.
