A System for Measuring Effects of Sulphur Dioxide on Gas Exchange of Plants

Abstract

Apparatus is described for exposing plants to low concentrations of SO₂ (50–500μg m⁻³ in air) and for measuring effects on photosynthesis, dark respiration, and transpiration. Temperature, humidity, and irradiance in the chambers were controlled independently, and fans ensured that leaf boundary layer resistances were low. Experiments with plants of Vicia faba in clean and polluted air showed that: (i) a depression of net photosynthesis by 50 μg m⁻³ SO₂ depended on boundary layer resistance and on irradiance; (ii) stomatal resistance was increased or decreased by 50 μg m⁻³ SO₂ when relative humidity in the chambers was low (35% r.h., 22 °C) or high (50% r.h., 22 °C) respectively.