||A Study of the Leaf Phenology and Thermonastic Leaf Movement of Daphniphyllum macropodum
Park, Seok–GonMatsumoto, Masaru
335 , 2017-09-08 , Faculty of Agriculture, Kyushu University
In this study, leaf phenology (the seasonal growth pattern of leaves) was investigated for 1 year to investigate the life–cycle strategies of Daphniphyllum macropodum. In addition, the degree of drooping and rolling of the leaves was measured at freezing temperatures in the winter, and the leaf moisture and leaf thickness were examined to determine the changes within the leaves. In April, young leaves unfolded in a flush, while the leaves that had emerged the previous year began to fall. The leaf longevity of D. macropodum was 12–17 months, and in spring, leaf unfolding and defoliation occurred almost simultaneously, avoiding self–shading. The leaves of D. macropodum are thick and wide; thus, old leaves block the light from young leaves, reducing their photosynthesis rate. Therefore, it is assumed that there is no need to keep old leaves on the branch for a long time. The phenomena of drooping and rolling were easily observed in the leaves of D. macropodum at –6.9°C, which disappeared at –3.6°C. There was no change in the moisture content of the leaves with the changes in the freezing temperature (below 0°C), but the leaf thickness decreased with the decreasing freezing temperature. This phenomenon is called thermonastic leaf movement, which may be a reaction to the freezing temperature in order to prevent excessive moisture loss in winter. It appears that at the freezing temperature, the water inside the cells migrates out of the cell and gathers together, resulting in a change in the leaf thickness.