Phosphate solubilization by organic anion excretion from rice (Oryza sativa L.) growing in aerobic soil

A mathematical model of P solubilization by organic anion excretion from ro ots is described and used to account for P solubilization by rice (Oryza sa tiva L.) plants growing in aerobic soil. In previous experiments with rice in an aerobic, highly-weathered, P-deficient soil, we found that the plants were able to solubilize P from an alkali-soluble pool and thereby increase their P uptake. The solubilization could not be explained by pH changes no r by the release of phosphatases. In subsequent experiments we found excret ion of citrate from rice roots into nutrient solutions, and the synthesis a nd excretion of citrate tended to increase under P starvation. The model al lows for the diffusion of the organic anion away from a root, its decomposi tion by soil microbes, its reaction with the soil in solubilizing P, and di ffusion of the solubilized P back towards the root as well as away from it. We calculated the rate of citrate excretion from rice roots growing in soi l based on measured steady-state citrate concentrations in the rhizosphere and calculated rates of decomposition. Calculations using these and other m odel parameters obtained independently showed that the observed solubilizat ion and increased P uptake by rice growing in soil could be accounted for. A sensitivity analysis of the model is given.