Effects of low-level ozone exposure under ambient conditions on photosynthesis and stomatal control of Vicia faba L.
Abstract. Gas exchange rates of 4-week-old faba bean plants were measured after exposure to ozonc (120 μg m3) in an open top chamber for 8 h per day over a period of 2 weeks. The exchange rates were compared with those of control plants. Plants exposed between mid-May and the end of July 1987 showed a minor negative effect on stomatal conductance, while there was no effect on photosynthesis and respiration. Plants exposed between the end of August and early October showed a negative effect on both stomatal conductance and photosynthesis. In addition, the dark respiration rate was slightly increased. It is concluded that ozone can have a direct effect on the stomata as well as on the photosynthetic system and that the stomata are more sensitive than the photosynthetic system.