Leaf expansion, carbon exchange rate (CER), mass carbon transfer (MCT), and carbohydrate pools were measured in one-year-old apple trees throughout the growing season. Two rootstocks, M.9 (full dwarf) and MM111 (vigorous) and 2 scion cultivars, ‘Redchief and ‘Northern Spy’ were used in all 4 combinations to give a wide range in growth vigor. Leaves of trees on MMIII had slightly higher CER than those on M.9. MCT was higher in ‘Northern Spy’ than in ‘Redchief’. Leaves of trees on MMIII had higher daily accumulations of starch and sorbitol than those on M.9; however, when these accumulations were expressed as a percentage of CER, the differences were not significant. ‘Northern Spy’ leaves showed no net dry weight gain over 24 hr, whereas ‘Redchief leaves did. About 17% of the leaf dry weight was not accounted for by nonstructural carbohydrates or MCT in ‘Redchief’ leaves. The morning starch concentration for all the trees increased throughout the season. The specific leaf weight of ‘Redchief was higher than for ‘Northern Spy’ on all dates. Specific leaf weight also increased throughout the season. Sorbitol accumulation rate in the leaf decreased from a mid-season high, whereas sucrose accumulation rate increased from mid-season. Starch accumulation rate in the leaf also decreased from a midseason high. Accumulation rates of starch and transport carbohydrates remained parallel throughout the growing season.
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Brown et al. (1985) studied this question.