The investigation concerns the influence of potassium on the transpiration rate of Triticum aestivum and Pisum sativum grown in nutrient solutions. Plants with high amounts of potassium were found to have the lowest transpiration rates. Shoot/root ratio, stomatal frequency, and stomatal aperture were correlated with the potassium concentration in the leaves. In Triticum no correlations with leaf concentration of Na were evident.Short term experiments were carried out in order to investigate the effects on the transpiration rate of a sudden increase in potassium concentration in the nutrient solution. An addition of potassium chloride to potassium deficient wheat plants resulted in a decrease in the transpiration rate of up to 50 "/o within two hours. Comparative tests with sodium chloride resulted in a decrease in transpiration rate of the same magnitude, indicating that the short-time reaction is not specific to potassium.The experiments show that the transpiration rate can be regulated by varied potassium and sodium concentrations. The observed effect is supposed to be due to changes in the stomatal aperture.

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