A Study of the Role of the Hydrogen Ion in the Mechanism of Potassium Absorption by Excised Barley Roots.

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Abstract
Rates of K and Br absorption by excised barley roots from solutions of KBr and KBr-CaBr2 mixtures were determined as a function of hydrogen ion concentration. The solutions were aerated and maintained at a constant temperature of 26[degree] C. The data showed that changes in hydrogen ion concentration of the solutions had a marked effect on the rate of K absorption. K absorption decreased with decreasing pH. The rate of Br absorption remained essentially constant throughout this pH range. It was concluded that the effect of hydrogen ion on K absorption must be interpreted as a direct hydrogen ion effect on the K accumulation mechanisms. The observed effects were consistent with the ion absorption hypothesis of Jacobson and Overstreet. The presence of Ca ion in solution was found to decrease considerably the depressing effect of hydrogen ion on K absorption. An explanation of this phenomenon in terms of the Jacobson-Overstreet hypothesis was presented. Increasing hydrogen ion concentrations depressed Na absorption from NaBr solution in a similar manner as K absorption from KBr solution.