Interactive Effects of Plant Growth-Promoting Rhizobacteria and Phosphates Sources on Growth and Phosphorus Nutrition of Soybean under Moderate Drought

The growth of legume plants is usually improved by the rhizobacteria inoculation under low phosphorus (P) and alleviation of P nutrition plays important role in plant drought stress response. The aim of this study was to assess the comparative efficacy of two plant growth promoting rhizobacteria namely Burkholderia cepacia B36 and Enterobacter radicincitans D5/23T combined with two sources of phosphates in soybean (Glycine max L.) under low water supply. Plants were grown under P soluble versus insoluble P fertilization for comparing the effects of soybean inoculation on growth, uptake and use efficiency of phosphorus under moderate drought stress. At the beginning of flowering, half of plants was subjected to low water supply (35% water holding capacity, WHC) for 12 days while control plants were well watered - 70% WHC. The plants were harvested at the end of drought and physiological traits and P contents were analyzed. The inoculation treatments showed better plant growth and nutrient uptake when compared to uninoculated control. The application of the Burkholderia cepacia was more efficiently in terms plant growth than E. radicincitans especially under insoluble phosphates. Phosphorus concentrations of shoots and roots increased with both bacterial strains. The bacterial inoculation has much better stimulatory effect on nutrient uptake by soybean fertilized with insoluble phosphates. Study findings indicate that the combined application of PGPR (Burkholderia cepacia B36) and P amendments has the potential to improve P nutrition and growth of soybean cultivated on P-deficient soil under well-watered as well as moderate drought condition