Photosynthesis in vine leaves as a function of light intensity, temperature, and leaf age

Abstract

Photosynthesis and respiration were measured in the laboratory with an infrared CO 2 analyser using attached leaves on Sultana vines growing either in the glasshouse or out of doors. At light saturation (2,500-3,000 f. c.) the photosynthetic rates approximated 8.5 and 10.5 mg CO/h/dm 2 with light compensation points of 50 and 125 f. c. respectively. The optimum temperature for photosynthesis was between 25 and 30° C. Age effects were examined using shoots from well established field vines. Small but rapidly expanding terminal leaves showed no net photosynthesis but had a high rate of dark respiration and a CO 2 compensation point above 300 ppm. With further expansion the leaves showed a steady increase in photosynthetic activity with a corresponding decline in dark respiration and CO 2 compensation point. The rate of photosynthesis again declined with the onset of senescence.