Effects of Varying N, P, K, Mg, and Ca Concentrations on Nitrogen Transport in Xylem Sap of Rice Plants

The nutrients absorbed in the plant roots are transported to the shoots through the xylem. The effects of concentrations of N, P, K, Mg, and Ca in a culture solution on N transport forms have not been fully elucidated. In this study, rice plants were grown with five concentrations of N, P, K, Mg, and Ca for three days, and the concentrations of major N compounds in the xylem sap were determined. In the control plants, nitrate, glutamine, and asparagine were the principal N compounds. The concentrations of nitrate, glutamine, and asparagine decreased consistently with a decrease in the N concentration in the culture solution. Different P concentrations did not affect the N components. With lower K concentrations, only the nitrate concentration decreased. While the glutamine and asparagine concentrations decreased with a decrease in the Mg concentration. The Ca concentration did not affect the N concentration, except for Ca deprivation. The citrate and malate concentrations markedly increased when the plants grew with an N-free solution due to regulating the cation-anion balance. The results of this study indicate that changes in the concentrations of N, K, Mg, and Ca affected the concentrations of N transport forms, especially nitrate, glutamine, and asparagine.