An assessment of the concentration of SO 2 to which plants are exposed in a system of chambers

Abstract

An assessment is made of the concentration of SO 2 to which ryegrass ( Lolium perenne L.) was exposed in a system of chambers developed by the first two authors. It is made in response to a criticism of the way in which the concentration was originally defined. The assessment is based on measurement of absorption of sulphur as SO 2 by the plants and on the total flux of SO 2 into the chamber. A simple mathematical model is used to determine the velocity of deposition of SO 2 (V g) to ryegrass and the decrease in concentration of SO 2 in air passing through the chamber. The mean velocity of deposition, on a leaf area basis, was 1·79 mm s −1 for plants grown as a simulated canopy. This is lower than values for isolated leaves or individual plants, and indicates that the decrease in SO 2 concentration is generally less than was suggested in the criticism. It is concluded that the higher growth rates of ryegrass in the authors' experiments than in experiments elsewhere, and the greater resistance to SO 2 absorption by a canopy than by isolated plants, largely account for the apparently low sensitivity to SO 2.