The Significance of the Suspension Effect in the Uptake of Cations by Plants from Soil‐Water Systems

Abstract

AbstractThe significance of the suspension effect (greater cation concentration or activity in the soil suspension than in the equilibrium dialyzate) in determining the uptake of cations by plant roots was evaluated by comparing the rate of uptake of Rb+ and Ca++ by excised roots of barley and mung beans from a suspension of clay or cation‐exchange resin with that from the corresponding equilibrium dialyzate. Although the cation concentration of the clay or resin suspension greatly exceeded that of the corresponding equilibrium dialyzate, the rate of uptake of Rb+ or Ca++ by the roots was found to be exactly the same from both the suspension and its equilibrium dialyzate.The results of this study are at variance with the prediction of the contact‐exchange theory but are in agreement with the deductions based on theoretical considerations of the consequences of the root surface or volume charge distribution. The significant conclusion that may be drawn, however, is that the composition of the soil solution or the equilibrium dialyzate should completely characterize the ionic environment of plant roots in soil‐water systems.