THE UPTAKE AND TRANSPORT OF CALCIUM IN THE FRUIT TREE

A study of the calcium economy of a fruit tree requires an understanding of the relative contributions that root uptake, remobilization and phloem transport make to the movement of calcium in the tree. Yet to reach such an understanding, we are forced to piece together information from a wide range of experimental data, and inevitably the result involves speculation. Much of the information which is available is analytical: calcium contents of fruit, xylem sap, leaves, petioles, wood and bark over the growing season; growth, yield and nutrient level responses to fertilizer regimes. However, there is also useful information on calcium uptake by roots, the behaviour of calcium in xylem and phloem, and the localization of calcium in various tissues and its deposition in different chemical forms.

What follows is an attempt to take a selection of experimental results from a number of sources, and to extract from them some basic principles of calcium transport in the tree. I have concentrated on three areas: root uptake, remobilization and phloem transport. Some original data presented below relate to Actinidia chinensis (kiwifruit or Chinese gooseberry) which for the purposes of this discussion is an honorary temperate fruit crop. The methods used in collecting this data are given below.