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

Abstract

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 CO2 uptake increased with leaf temperature to 2.7 g CO2 m2hr-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/m2 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 CO2 m-2hr-l.