The adsorbent capacity of growing media does not constrain myo-inositol hexakiphosphate hydrolysis but its use as a phosphorus source by plants

Aims The hydrolysis of organic P in soils is a relevant aspect contributing to the supply P to plants, which is affected by adsorbent capacity and biological properties of soils. This work aimed at studying the contribution of phytate to plant nutrition as affected by Fe oxides and phosphohydrolases releasing microorganisms in the growing medium. Methods An experiment with cucumber and myo -inositol hexakiphosphate ( myo -Ins6P) as P source was performed involving two factors: Fe oxide –ferrihydrite– rates (0, 100, 300 mg kg −1 of citrate–ascorbate extractable Fe), and microbial inoculation ( Trichoderma asperellum T34, Bacillus subtilis QST713, and non-inoculated). Results P uptake decreased with increased Fe oxides in the growing media. Phytase activity and organic anions concentration increased with increased Fe oxides in the media. Most of the P supplied was recovered as inorganic P at the highest Fe oxide concentration. Inoculants did not improve P uptake by plants, despite B. subtilis promoted an enhanced hydrolytic activity at the highest Fe oxide concentration. Conclusions An increased adsorption capacity of the growing media restricts the use of myo -Ins6P as P source by plants. This was not the result of its stabilization through adsorption or a decreased hydrolytic activity, but of the adsorption of inorganic P on Fe oxides after hydrolysis.