Increased proton extrusion of wheat roots by inoculation with phosphorus solubilising microorganims

There is not much information on the mechanism(s) by which phosphate solubilizing microorganisms (PSM) increase plant phosphorus (P) uptake. Studies with PSM inoculated wheat plants grown in both microcosms and rhizoboxes were conducted to determine whether inoculations with PSMs acidify rhizosphere. Significant (P < 0.05) increases by bacterial inoculation were obtained in rate of proton efflux by roots (by the strains # 67, 189, and 73), plant P uptake (by # 169 and 189), K uptake (by # 67, 189, 73, 169, and 145), and uptake of P against the uptake of Ca and Mg (by # 67, 189, 73, 169, and 145) in a calcerous soil without fertilization. Only Bacillus sp. # 189 significantly (P < 0.05) raised available P in the rhizosphere. Plant available P by Olsen extraction in the control and the # 189 inoculation were 6.3 and 8.0 mg kg(-1), respectively. The root induced acidification in nutrient solution with ammonium (NH (4) (+) -N) supply by inoculation of Bacillus sp. # 189 was confirmed in a rhizobox experiment when nitrogen source was NH (4) (+) -N. Enhanced proton extrusion by plant roots accompanied probably by the release of extra organic acid anions may contribute to mobilization and uptake of P in Bacillus sp. # 189 inoculated wheat plants in this study. The changes in total uptake and balance of nutrients in the PSM inoculations imply a modification of plant cell metabolism.