Modification of Stomatal Conductance by Sulphur Dioxide

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Abstract
The mechanism of SO2-induced changes in stomatal conductance (g) of alder was examined to determine if SO2 affects guard cell function directly or indirectly through the SO2-induced changes in photosynthesis. During experimental fumigations at SO2 concentrations of 3–3 μmol m−3 (0.08 μl l−1), stomatal closure preceded declines in net photosynthetic rate (A), indicating that SO2 can directly affect guard cells. From these and other studies it appears that the sequence of A and g responses may be influenced by SO2 concentration as well as by species. Fumigation with SO2 did not cause increases in g, even when the intercellular substomatal CO2 concentration (ci) was reduced by 50 μmol mol−1. Increases in g are not attributable to SO2 effects on the CO2-based stomatal control system.