Abstract
This paper reports on the effect of leaf water potential on growth of satsuma mandarin (Citrus unshiu MARC.) trees.
1. In late August, fruit diameters began to shrink from about thirty minutes after sunrise, continued to contract during the day and began to increase near the time of sunset. The amplitude of diurnal contraction and expansion which became more pronounced with reduction in leaf water potential (φmax), before sunrise became conversely smaller when φmax dropped below -12 bars, because of no full recovery occurring at night.
2. Growth of fruits and trunks was more sensitive to leaf water stress than that of leaves. Fruits and leaves stopped to grow when φmax dropped to about-8 bars and -15 to -20 bars, respectively.
3. Leaf water potential(φmin)and leaf diffusion resistance (RL) measured between 1:00 and 2:00p.m. were also related to fruit growth. Fruit growth stopped completely when φmin and RL reached -17 bars and 16sec/cm, respectively. In a shaded tree, however, fruit growth stopped at -9 bars of φmax (2 bars lower than an unshaded tree) and 16sec/cm of RL, but φmin seemed to have no effect on daily fruit growth.
As a result of this experiment, among φmax, φmin and RL, fruit growth was closely related to RL and φmax, but it is necessary to exercise caution in interpreting RL because RL was highly sensitive to changes in solar radiation. In the field work, then, it may be quite all right to consider that φmax can be used in estimation of plant growth.
