クロマツ苗木の水ポテンシャルと生長応力

抄録

In this study, the water potential (WP), stem strain and growth strain on surface in young Japanese black pine (Pinus Thunbergii Parl.) were measured at intervals during a single day in various seasons in order to investigate the evolution process of growth stress in young Japanese black pine.
The results obtained are summarized as follows.
(1) From the relationship between the changes of xylem contained in the stem and the WP during a single day in various seasons, the WP of all trees was found to increase steadily for about 4 hours after sunrise from the minimum value at dawn, and become constant at that level until about 2 hours before sunset, and then decrease steadily to the minimum of the following day. The stem strain reached a minimum value at the time when the WP remained high in its value, and then increased steadily toward the maximum value of the following day, corresponding to the decrease of WP. It was suggested that the stem strain in xylem was about 15% of the stem with bark.
(2) The change in growth strain on the surface during a single day could be shown by a curve with a maximum for all seasons. The growth strain on the surface in all trees reached a maximum after 2 to 4 hours after sunrise, and then decreased gradually to reach a minimum near sunset. Those results on the growth strain on the surface seems to suggest that the change in growth strain on the surface during a single day is connected with the change in WP.
(3) Though the trees examined at various seasons contained different conditions of cell wall, the change of the growth strain on surface during the whole day was almost the same for all trees. The seasonal change of growth strain on surface was observed in the distribution of the growth strain on surface at a certain height of tree. It appeared clearly on top of trees, but not so at breast height.