MAXIMUM PHOTOSYNTHETIC RATE‐A CASE STUDY IN APPLE

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Abstract
SUMMARY: Widely different rates of carbon dioxide assimilation by apple leaves have been reported. Data from forty‐nine papers are examined and likely reasons for their variation are deduced. Many studies were made on glasshouse‐grown plants, the leaves of which can have a very different structure and photosynthetic capacity from those grown outdoors. Other biological aspects including the influence of fruits are discussed. Leaf temperatures have rarely been measured but there is evidence that excessive temperatures occurred in some studies and many other assimilation rates were probably decreased by less obviously extreme conditions. The rates of air flow employed have often been inadequate for true assimilation rates to be obtained. However, many rates higher than those normally quoted have been obtained by several workers including the author and it is concluded that the maximum photosynthetic rate of apple leaves in normal air is at least 35 mg CO2 dm−2 h−1.