Tricalcium-phosphate solubilizing efficiency of rhizosphere bacteria depending on the P-nutritional status of the host plant

Abstract

This study assesses the influence of saccharides in the rhizodeposition on the phosphate solubilizing ability of rhizosphere bacteria. Water-soluble rhizodeposits were analysed of ¹⁴C labelled pea plants (Pisum sativum) which were grown at two different levels of P-nutrition. The sugars produced were fed in vitro either as single compounds or as synthetic mixtures to three bacterial strains and the ability of the bacteria to mobilize Ca₃(PO₄)₂ was measured. The ability of Pseudomonas fluorescens (PsIA12) to dissolve tertiary calcium phosphate was lower with sugars of the P-deficient plants than with glucose. On the other hand, sugars of P-deficient plants increased the P-mobilizing ability of Pantoea agglomerans (D 5/23) and Azospirillum sp. (CC 322) considerably. The production of different carboxylic acids was responsible for these effects.