Carbon Flux in Apple Trees: The Effects of Temperature and Light Intensity on Photosynthetic Rates1

The effects of light intensity and leaf temperature on the net photosynthetic rate of rapidly growing ‘Golden Delicious’ apple ( Malus domestica Borkh.) shoots were determined in a temperature range (-1.6 to 44°C) broader than previously reported. Under saturating light conditions the rate of CO 2 uptake increased with leaf temperature to 2.7 g CO 2 m 2 hr -1 at 25°. Optimum temperature decreased as the light intensity decreased, indicating a relationship between temperature and light saturation levels. At 25 to 30° the light saturation point was equivalent to 86 W/m 2 of incident electromagnetic energy at wavelengths of 400 to 750 nm. At temperatures higher than the optimum, the rate of carbon dioxide uptake decreased rapidly. At 47 to 50° and high light intensities, the rate of carbon dioxide uptake was 0.3 to 0.5 g CO 2 m -2 hr -l .