Exchange acidity of wheat and pea roots in salt solutions

Abstract

The pH of salt colutions of different kinds and concentrations was lowered when roots of starved peas (Pisum sativum) and wheat (Triticum aestivum) plants were submerged. This pH decrease seems to be primarily caused by cation exchange. The metal cations of the salts displace hydrogen ions on the root surface. The root surface functions as a cation exchanger in a way that can be predicted by the ordinary ion exchange laws. Effects of concentration, valency, and hydration of salt cation were demonstrated in the experiments. These exchange properties of the roots are marked and consistent at +20°C as well as at +0.5°C with N2-gas bubbling. At 0.5°C the cell metabolism is reduced to a minimum and no active uptake or release of ions from the roots can occur. The exchange acidity of the roots increased with the salt concentration and with the valency and hydration in the order: M+<M2+<M3+ and Li<Na<K; Mg<Ca<Ba.