Fig. 5.

Time courses of stomatal conductance (g _sw) when the upper foliage of well-watered and water-stressed Assiniboine plants was exposed to a reduction in ambient CO₂ concentration (C _a ~75 μmol mol^–1). Different levels of water stress were examined, expressed here as the percentage of g _sw relative to their initial well-watered state (g _{sw_ini}) evaluated 7 d prior to the low C _a treatment (black circles, well-watered, where g _sw increased compared with g _{sw_ini}; dark grey circles, 44% of g _{sw_ini}; light grey circles, 15% of g _{sw_ini}; and white circles, 6% of g _{sw_ini}). The short arrows indicate when C _a was increased from ~75 μmol mol^–1 to a CO₂ concentration resulting in a C _i of ~275 μmol mol^–1. The data points to the right of the arrows were measured at that C _i, showing the high sensitivity of severely stressed plants to the return to near ambient C _a.