Abstract: | Apparatus is described for exposing plants to low concentrationsof SO2 (50500µg m3 in air) and for measuringeffects on photosynthesis, dark respiration, and transpiration.Temperature, humidity, and irradiance in the chambers were controlledindependently, and fans ensured that leaf boundary layer resistanceswere low. Experiments with plants of Vicia faba in clean andpolluted air showed that: (i) a depression of net photosynthesisby 50 µg m3 SO2 depended on boundary layer resistanceand on irradiance; (ii) stomatal resistance was increased ordecreased by 50 µg m3 SO2 when relative humidityin the chambers was low (35% r.h., 22 °C) or high (50% r.h.,22 °C) respectively. |