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MINERAL ABSORPTION AND DISTRIBUTION IN YOUNG APPLE TREES UNDER VARIOUS ENVIRONMENTAL CONDITIONS
This of course holds especially for the absorbing organ itself — the root — where, for example, soil temperature may directly affect the process of absorption.
In addition, the uptake of minerals may be influenced indirectly by above-ground conditions via effects on shoot growth.
Thus, Russell (1972, 1977) concluded that uptake of nutrients by intact growing plants is often controlled predominantly by the metabolic demands of the plant and not by factors in the root system.
Likewise, on the basis of work with peach seedlings, Richards and Rowe (1977) suggested the existence of a functional equilibrium between root and shoot with respect to nutrient uptake.
Relatively little is known about nutrient uptake by woody plants under various environmental conditions, and especially long-term uptake.
Information on this point might be useful for apple and pear, since the incidence of certain economically important storage disorders in pome fruits, such as bitter pit and internal breakdown in apple, appear to be related to mineral deficiencies (Faust and Shear, 1968; Bangerth, 1969). The weather during the growing season is an important factor in this respect, as Wilkinson (1968) pointed out and has also been shown by Wiersum (1979) in a recent comprehensive review on calcium nutrition.
In the present series of experiments carried out under otherwise constant conditions, the effect of relative air humidity, soil moisture content, root temperature, and light intensity on the behaviour of young apple trees was studied.
For convenience and simplicity, one-year-old apple rootstock clones of different vigour and bearing one bud of Cox’s Orange Pippin were chosen as plant material.
A limited number of data on uptake and distribution of calcium and potassium in one or two rootstock-scion combinations will be discussed.
Growth and water use will only be considered where relevant.
The effect of root temperature has already been discussed in some detail in a previous paper (Tromp, 1978).