High phosphorus fertilization changes the speciation and distribution of manganese in wheat grains grown in a calcareous soil

The physiological disorders in humans resulting from the excess dietary intake of manganese (Mn) via whole-grain food has attracted considerable attention. However, the speciation and bioavailability of Mn in wheat grains and their response to different phosphorus (P) fertilization rates are still unclear. In the current study, using a long-term field trial with P application rates of 0, 21.8, 43.6, 65.5 and 87.3 kg/ha, we examined changes in the concentration, distribution, and speciation of Mn of wheat grains using synchrotron-based X-ray fluorescence microscopy and X-ray absorption spectroscopy. The total Mn concentration in grains was found to be increased by phosphorus fertilization, especially in embryo in the form of Mn(II), but this phosphorus fertilization also decreased Mn concentrations in the nucellar projection. In this study, the speciation of Mn in different wheat grain tissues was examined, and results indicate that in calcareous soils, high rates of P fertilizers can increase Mn concentrations in wheat grain, including Mn which is likely to be of high bioavailability, and thus may increase the risk for human to expose to high Mn intake via whole-grain food.