林木稚苗の蒸散, 吸水作用の日変化および両作用に及ぼす外的環境因子の影響

Abstract

This report deals with the effect of three environmental factors (light intensity, wind velocity and concentration of culture solution) on the rates of transpiration and absorption of water in the seedlings of some species (Cryptomeria japonica D. Don. (Sugi), Chamaecyparis obtusa Sieb. et Zucc. (Hinoki) and Pinus densiflora Sieb. et Zucc. (Akamatsu). For the purpose of studying the effect of a certain external factor, it is necessary to control other conditions. For this reason, these experiments were performed in the phytotron (temperature 20℃, humidity 60%). The outline of these results is as follows; 1) The diurnal changes of transpiration and absorption have a close relation with light intensity. (Fig. 2, 3) The maxima of these two functions occurred near midday, while the minima came at midnight. Transpiration and absorption showed similar diurnal changes, but absorption slightly lagged in time behind transpiration. And the maximum absorption was a little lower than the maximum transpiration, while the minimum absoption was higher than the minimum transpiration. Besides, the results of these experiments showed no essential difference among species and by seasons. 2) The effect of the artficial light on the rates of transpiration and absorption is also remarkable. (Fig. 4, Tab. 2) Transpiration and absorption at 40, 000 lux were three times as large as those at 500 lux. But these increasing rates of transpiration and absorption caused by the increases of light intensity reduced as wind velocity became higher, and this tendency was observed more clearly when concentration of culture solution became thicker. After the osmotic value of the solution became over 2at. and the wind velocity over 2.2m/sec. the further increases of light intensity did not cause any noticeable increases in transpiration and absorption, only 10% increase at 5, 000 lux. 3) The wind also gives a noticeable influence upon the rates of transpiration and absorption. But the effect of this factor differs according to other conditions. Namely, when the other factors hardly encouraged transpiration and were profitable to absorption (for example: dim light and dilute culture solution), these two functions increased with wind velocity, although in the opposite conditions, these two functions decreased with the increase of wind velocity. 4) The increase of concentration of cultnre solution caused the decreases of transpiration and absorption. The decreases of the two functions were almost linear while the concentration of the solution was below 4at. (the osmotic value), but slowed down remarkably at 4at. and over. Particularly the transpiration hardly over decreased above 4at..