I. Studies on the Photosynthetic Activity in Several Kinds of Fruit Trees

I. Effect of some Environmental Factors on the Rate of Photosynthesis

Abstract

1. The photosynthetic activity was compared among several kinds of fruit trees and grape vines in relation to some environmental factors. The rate of photosynthesis was determined with intact leaves remaining on potted trees by means of an infrared CO₂ analyzer.
2. Photosynthesis was considerably influenced by the rate of air movement. Maximum photosynthetic activity was observed at the air flow rate of about 1 liter/dm²/min in peaches, grapes and chestnuts, while in Japanese persimmons, figs and satsuma mandarins, it was 2 liters/dm²/min. The rate of photosynthesis of the former group began to decline when the rate of air movement became higher than optimum. In the latter group, however, there existed no such evidence.
3. Saturating light intensity for the photosynthesis of intact leaves was approximately 40klux in Japanese persimmons, figs, peaches, chestnuts and satsuma mandarins, and 30klux in grapes.
4. Satsuma mandarin trees were grown in various light intensities between 8 and 100klux. The thickness of leaf blade and palisade parenchyma, number of stomata per mm² were all decreased with lowering light intensities, whereas leaf areas increased.
5. Optimum leaf temperature for the photosynthetic activity was about 25°C in grapes, figs and satsuma mandarins, 30°C in peaches and 20°C in Japanese persimmons and chestnuts. At higher temperatures than optimum, the photosynthetic activity was decreased rapidly with increasing leaf temperatures in Japanese persimmons, figs, peaches and chestnuts, but in grapes and satsuma mandarins it was lowered gradually.