Effects of Anions and Cations on Potassium Absorption by Plants of High Potassium Chloride Content

The effect of anion type and increasing calcium and sodium concentration on short-term potassium absorption by barley plants grown in nutrient solutions containing KCl was studied; the aim was to determine if such KCl-pretreated plants have the same potassium-absorption characteristics as KCl-starved roots. At a concentration of 20mM potassium, KCl-pretreated plants absorbed potassium from chloride solutions 1.5 times as fast as from sulphate solutions, and faster from nitrate than from chloride solutions. However, at 0.5 mM potassium, absorption rates from nitrate and chloride solutions were similar, as were rates from sulphate and chloride solutions at concentrations of 0.5 mM potassium or less. These results suggest that KCl-pretreated plants have both an anion- independent and an anion-controlled component of potassium absorption. In 0.5 mM KCl, high concentrations of calcium and sodium chlorides, but not sulphates, stimulated potassium absorption by KCl-pretreated plants. It is suggested that high rates of chloride absorption may stimulate potassium absorption from concentrations of potassium below 1 mM. In 20 mM KCl, neither chlorides nor sulphates of calcium or sodium had any effect on potassium absorption into KCl-pretreated plants. This result contrasts with published results with KCl-starved roots. The different results are interpreted as an increase in selectivity for potassium over sodium with increasing time of treatment with potassium.