Figure 1.

Light response curves of net O₂ evolution at 2.5% CO₂ for V. riparia leaves at the beginning of the growing season. Values are average ± ses of three to five replicates. Curve 1 was measured October 31 (after several days with mean temperatures above 25°C and minimum night temperatures above 10°C). Curve 2 was measured November 3 (mean temperature previous days, 17°C; minimum night temperature, 8°C–9°C). Curve 3 was measured November 5 (mean temperature, 18°C; minimum night temperature, 9°C). Curves 4 to 6 were measured on November 6, 7, and 9, when the mean temperature increased to 25°C and minimum night temperatures were 11°C. Values of the quantum yield of O₂ evolution (average ± se): curve 1, 0.074 ± 0.009; curve 2, not measured; curve 3, 0.038 ± 0.013; curve 4, 0.038 ± 0.002; curve 5, 0.047 ± 0.013; curve 6, 0.099 ± 0.014. Corresponding values of dark-adapted F_v/F_m (average ± se) were; curve 1, 0.809 ± 0.010; curve 2, not measured; curve 3, 0.812 ± 0.005; curve 4, 0.822 ± 0.003; curve 5, 0.818 ± 0.04; and curve 6, 0.821 ± 0.003.