Effects of coinoculation of Rhizobium with plant growth promoting rhizobacteria on the nitrogen fixation and nutrient uptake of Trifolium repens in low phosphorus soil

Low soil phosphorus (P) availability is a notable limitation for legume nodulation, nitrogen fixation and yield, and it is therefore important to improve legume growth under P-deficient conditions. This study aimed to determine the effects of coinoculation with Rhizobium and plant growth promoting rhizobacter (PGPR) on the nitrogen fixation and nutrient uptake of white clover (Trifolium repens) in a P-deficient soil. White clover plants were inoculated with one of the two Rhizobium strains CHB1120 and CHB1121 alone or coinoculated with either of the Rhizobium strains and one of the two PGPR strains, Bacillus aryabhattai strain Sb and Azotobacter vinelandii strain G31. White clover inoculated with either CHB1120 or CHB1121 alone and coinoculated with one of the two Rhizobium strains and the PGPR significantly enhanced nodule numbers compared with the non-inoculated control. The coinoculation of either CHB1120 or CHB1121 and Sb showed a significantly greater level of nitrogenase than the single inoculation of CHB1120 or CHB1121. In addition, the single inoculation of CHB1120 or CHB1121 and their coinoculation with PGPR significantly increased nitrogen contents in both shoots and roots under P-deficient conditions. The coinoculation of CHB1121 and G31 showed the greatest N content in shoots. Moreover, the single inoculation of the two Rhizobium strains and their coinoculation with G31 and Sb significantly increased the K, Ca, and Mg contents in shoots compared with the non-inoculated control. In summary, the PGPR used in this study can enhance the symbiotic potential of rhizobia under low P conditions.