Photosynthesis in Relation to Growth and Distribution of Fruit in Peach Trees

Abstract

The rate of photosynthesis and the total daily photosynthesis of a peach tree [Prunus persica (L.) Batsch.] were found to be closely related to changes in carbon requirements caused by changes in the stage of fruit growth and by fruit removal at harvest. Although the light regime was superior in the topmost zone of leaves, the rate of photosynthesis was lower than in intermediate zones during the period of most rapid fruit growth. In contrast, the rate of photosynthesis in the horizontal zones of the tree was closely related to the weight of fruit per unit of leaf area in each zone. This coupling between supply and demand was also demonstrated by assimilate build up in the leaf when fruit were removed, i.e. 14C turnover was substantially reduced. During the final stage of rapid fruit growth (DW III) the growth of fruit was stimulated above and inhibited below a cincture through the phloem of the main branches, which indicated that the level of assimilate available for fruit growth was lower in the bottom of the tree. This conclusion was supported by the observation that the mean leaf density (mg dry weight/cm�) increased with increasing height in the canopy. It was concluded that the data were good evidence of a strong coupling between the supply of assimilates by the leaves and the growth requirements of the tree.