PHOSPHATE SOLUBILIZING MICROORGANISMS: MECHANISM OF SOLUBILIZATION AS INFLUENCED BY PH, TYPE OF ORGANIC ACID AND SUGARSN. NARULA, A. DEUBEL, A. GRANSEE AND W. MERBACH
Phosphate solubilizing isolates ITom rhizosphere of eternal rye (Secale cereale) from long term experiment (Narula et al. 2002) and reference strains of A. chroococcum, Pantoea, Pseudomonas were compared for p- solubilizing ability over a period of 18 days. Based on quantitative analysis of acids and sugars produced during phosphate solubilization process, a possible mechanism for phosphate solubilization in chosen strains (zone formers and non zone formers) is postulated. Phosphate solubilization increases with the incubation time of 0-18 days with some concomitant decrease in pH almost in all the isolates studied except in Azotobacter chroococcum Ala-27. Highest solubilization was observed in ER 3 (84.45 vg P m1-1) and ER 10 ( 59.68) followed by Mac 27 and MSX-9. Apart from citric, malic, succinic, lactic and fumaric acids some new acids like gluconic, malonic (ER-I0), isocitric also (ER-3) appeared. Sugar concentration was quite high which decreased with the rise in P solubilization and organic acids. One of the possible mechanism of P solubilization from our studies could be the appearence of new sugar alcohols like arabitol, mannitol, adonitol, meso-erythritol and maltitol and rise in organic acids (although low) without much effect on pH. Cumulative effect of all these factors might have an indirect effect on P solubilization,
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