Figure 2.

Stomatal conductance (A and D) and assimilation (B and E) measured on the first fully expanded leaves of V. faba plants during exposure to charcoal-filtered air containing 0 (□), 0.10 (▴), or 0.18 (●) μl⋅liter⁻¹ O₃ for 4 hr in continuous stirred tank reactors (24). (A–C) The plants were kept in the dark overnight and until the start of exposure to allow observation of the influence of O₃ on light-induced stomatal opening (natural illumination supplemented with 150 μmol⋅m⁻²⋅s⁻¹). Both O₃ treatments resulted in significant (P < 0.01) reductions in stomatal conductance and assimilation. (D–F) The plants were kept in the light (natural illumination supplemented with 150 μmol⋅m⁻²⋅s⁻¹) for 4 hr before exposure to ensure open stomata at start of exposure. Only the highest O₃ treatment resulted in significant (P < 0.01) reduction of stomatal conductance (after 3 and 4 hr) and assimilation (after 4 hr). In each replicate experiment, gas exchange was measured on five individual plants for each treatment/time point. (C and F) Assimilation (A) versus intercellular CO₂ concentration (C_i) measured within 60 min after the end of O₃ exposure, on the first fully expanded leaf of two individual plants for each treatment. The average A/C_i curve for the plants exposed to 0.10 μl⋅liter⁻¹ O₃ was not significantly different from that of plants exposed to charcoal-filtered air whereas plants exposed to 0.18 μl⋅liter⁻¹ O₃ had significantly lower A/C_i curves (P < 0.05). For all panels, the average of three experiments is shown.