Interactive effects of rhizobacteria inoculation and phosphorus on proline and nitrogen contents in roots and nodules of soybean grown under constant P insufficiency and water deficit

Abstract

Plant osmolytes play an important role in plant tolerance to abiotic stress factors.A greenhouse experiment with soybean was carried out with N-fixer rhizobacteria Bradyrhizobium japonicum applied singly or in combination with P (20 and 100 mg kg-1dry soil) and two soil moisture regimes: 70% of whole holding capacity (WHC) as control and water stress 35% WHC. All plants were grown under same moisture conditions until the flowering stage. Water deficit conditions were imposed at flowering stage of plants for 12 days. Plants cultivated under the combined effects of P deficiency and drought exhibited the highest proline accumulation. Soybean inoculated with B. japonicum showed increased root proline concentrations compared to uninoculated plants subjectedto temporary water deficit. Integrated use of inoculation and a moderate dose of P had a synergic effect on free proline accumulation in roots. The results revealed that combined influence of drought and P insufficiency significantly increased proline concentrations in nodules rather than in roots.Integrated use of rhizobacteria strain and a moderate dose of P decreased free amino acid accumulation in nodules under drought.There was a synergic interaction between the rhizobacteria strain and P in terms of leaves and stems nitrogen contents of soybean. In conclusion, soybean inoculation with B. japonicum in conjunction with P fertilization partially attenuates the adverse effects of constant low P availability and temporary drought on plants.