Mechanism, influencing factors and practical application of organic acids in improving soil phytate bioavailability

Phytate in soils mainly origins from plant residues and monogastric animal excrement. The phytate can only be mineralized to release P through hydrolysis and dephosphorylation, which are catalysed by specific enzymes-phytase (myo-inositol hexakisphate phosphohydrolase). Phytic acids or phytate, are important components of soil organic phosphorus, accounting for 50%–80% of total organic P. Phytic acids contain 6 phosphate groups and 12 dissociable protons, thus readily being adsorbed by soils or form insoluble complexes with metal ions. Consequently, phytic acids are prevented from interactions with phytase, their decomposition and mineralization efficiency are thus decreased greatly, hard to release P for plant uptake. Improving the solubility and bioavailability of phytate is one of the prerequisites to ensure the efficient P supply of soil to crops. Soil organic acids are derived from plant root excretes, microorganisms, and organic matter decomposition. Organic acids have plenty of functional groups, which can form more stable ligand complexes with metal ions, therefore, mobilize the adsorbed phytate or phytate-metal complexes through competitive adsorption, complexation, and fracturing organic matter-metal bridges. The kinds and contents of soil organic acids varied, depending on plant and microbe species. Besides, soil pH, organic matter content, the types and contents of soil minerals/metal oxides all influence the mobilization efficiency of organic acids-mediated phytate. As such, further studies should work on the following points: 1) Phytate mobilization efficiency of different organic acids in different types of soils. Quantitatively analyze phytate desorption and mobilization efficiency by different kinds and concentrations of organic acids. 2) Phytate-adsorped mineral surface is highly negative charged in wide pH ranges, which hinders the adsorption and displacement reactions of organic acids. Therefore, it is necessary to explore strategies to improve the mobilization of adsorbed-phytate. 3) Monitoring and evaluate the long-term performance of organic acids-mediated phytate mobilization.