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.
Pear leaf assimilation and transpiration were measured under both laboratory and field conditions using infrared gas analysis.In the laboratory, leaf resistance to water vapour loss !rI) was c. 1 · 2 sec cm-1 at a saturating light intensity, and the m esophyll resistance to C02 uptake (r;" ) was 4 ·4 sec cm-I . These relatively low diffusive r esistances were in line with the high rates of photosynthesis recorded in both the laboratory and field.The effect of leaf water potential and the nitrogen status of the tree on leaf photosynthesis was studied in the orchard. Photosynthesis was not immediately affected until leaf water potential had fallen to below -30 atm, although a history of water shortage reduced the daily maximum rate of photosynth esis. Similarly, trees that experienced a prolonged nitrogen deficiency showed a lower rate of leaf photo. synthesis in terms of both leaf area and chlorophyll concentration although the leaves recovered their green colour and photosynthetic activity following nitrogen fertilization. I . INTRODUCTIONDespite the economic importance of pear trees, there is no detailed report in the literature on the photosynthetic activity of their leaves. The present paper attempts to document this information, and to provide background data for decisions relating to tree management. Accordingly, pear leaf photosynthesis was studied in relation to certain environmental and nutritional factors under both laboratory and orchard conditions. II. MATERIALS AND METHODSWell.developed pear trees, Pyrus communis (L.) cv. Williams' Bon Chretien (syn. Bartlett), were used for all experiments. Budded trees growing in pots were u sed for the laboratory studies, while mature (30.yr·old) trees growing in the orchard or l.yr·old trees in sand culture (out·of-doors) were used for the field m easurements at Tatura. The trees growing in sand culture had been maintained on complete nutrient solution (Hewitt 1966), with the exception of nitrogen. Two levels of nitrate were imposed: 12 m.equiv/l which was regarded as adequate and which promoted vigorous tree growth; and 1 m.equiv/l which was suboptimal and caused reduced growth plus foliar chlorosis. These two nutritional planes provided contrasting material for experimental purposes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.