Phytate exudation by the roots of Pteris vittata can dissolve colloidal FePO₄

Phosphorus (P) is limiting nutrient in many soils, and P availability may often depend on iron (Fe) speciation. Colloidal iron phosphate (FePO_4coll) is potentially present in soils, and we tested the hypothesis that phytate exudation by Pteris vittata might dissolve FePO_4coll by growing the plant in nutrient solution to which FePO_4coll was added. The omission of P and Fe increased phytate exudation by P. vittata from 434 to 2136 mg kg^-1 as the FePO_4coll concentration increased from 0 to 300 mM. The total P in P. vittata tissue increased from 2880 to 8280 mg kg^-1, and the corresponding increases in the trichloroacetic acid (TCA) extractable P fractions were inorganic P (860-5100 mg kg^-1), soluble organic P (250-870 mg kg^-1), and insoluble organic P (160-2030 mg kg^-1). That is, FePO₄-solubilizing activity was positive correlated with TP, TCA P fractions in P. vittata, TP in growth media, and root exudates. This study shows that phytate exudation dissolved FePO_4coll due to the chelation effect of phytic acid on Fe; however, the wider question of whether phytic acid excretion was prompted by deprivation of P, Fe, or both remains to be answered.