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  • Author or Editor: Robert A. Kennedy x
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Abstract

Potted sweet cherry (Prunus avium L.) trees, grown under constant environmental conditions, were used to determine characteristics of leaf photosynthetic development separate from environmental influences. A maximum rate of photosynthesis of 38 mg CO2/dm2 (per hour) was reached at a leaf plastochron index (LPI) of 10, which is about 80% of full leaf expansion. During development, CO2 compensation points decreased to about 25 μl·liter−1 CO2 at LPI 12, but gradually increased to a value of about 35 for mature leaves. Of 3 leaf ages studied, (LPI 5, 10, and 15) response to low O2 was the least at LPI 10. Carboxylation efficiency doubled between LPI 5 and 10, while stomatal conductance was highest and mesophyll resistance was lowest from about LPI 10 to 13. Light saturation occurred at about 500 μmol·s−1·m−2, and optimal temperature for photosynthesis in sweet cherry was 19° to 25°C. Light and temperature effects were apparently independent of leaf age. Our results indicate major influences of leaf development on photosynthesis in sweet cherry and serve as the basis of continuing studies aimed at the importance of leaf developmental stage for cultural and production practices.

Open Access

Abstract

For all leaf ages of Rosa hybrida L. cv. Samantha, maximum photosynthetic rates were reached at irradiances of 450 to 500 μE m−2sec−1. The magnitude of this response decreased from 20.6 mg CO2 dm−2hr−1 in the youngest leaves studied to 15.4 mg CO2 dm−2hr−1 in the oldest. Maximum photosynthetic rates were reached before full leaf expansion. Mesophyll resistance, however, increased with age from 7.8 to 12.5 cm sec−1. CO2 compensation points and dark respiration decreased throughout most of leaf development, but increased slightly at the most advanced developmental ages studied. Photosynthetic enhancement, the percent increase in net photosynthesis at 2% O2 compared to 21% O2, averaged 33% for all leaves. There was no change in the amount of photosynthetic enhancement as leaves aged, indicating that changes in photorespiration were not a major factor in photosynthetic trends over the range of leaf ages examined.

Open Access

Abstract

The rate and efficiency of photosynthesis (PS) is unquestionably one of the primary determinants of crop yield. Yet, as this symposium illustrates, many other factors contribute to plant productivity. Indeed, the exact relationship between PS rate and yield remains undefined. For several years we have now been interested in factors that affect PS rate in both C3 and C4 plants, not only within the plant, but also external to it. Internal factors affecting PS that will be discussed include leaf age, leaf canopy, photorespiration, stage of plant development (including both vegetative and reproductive phases), and the occurrence of little-recognized metabolic pathways such as polyol synthesis and transport. External factors that affect PS, in addition to obvious environmental determinants such as temperature, light, and water, include the seasonal growth cycle. While we still do not understand how all of these factors interact to affect yield, we are beginning to understand their singular effects. Control of these factors, once thought to be within reach even before the advent of biotechnology, remains likely, but distant.

Open Access