The intake curve for calcium into apple fruits under various environmental conditions

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Abstract
The effect of a few environmental factors on calcium intake into fruits was studied in potted trees (cv. Cox's Orange Pippin and Schone van Boskoop) kept under either fully controlled or outdoor conditions. Contrary to the usual pattern of orchard trees, the intake curve did not flatten after mid‐July but showed a substantial increase which persisted until harvest. Only at a root temperature of 6°C did Ca intake slow down appreciably. It is postulated that this additional Ca movement may occur in the phloem and may be controlled by the rate of fruit growth. It is suggested that, in orchard trees after mid‐July, the intake of Ca into the fruits is counterbalanced by Ca leaving the fruit in the water flowing back at high water stresses occurring within the tree during the day. Under more or less controlled conditions, when water stresses are much less pronounced, back‐flow of water and Ca will not occur, except under extreme conditions, such as a root temperature of 6°C.