シラベ前生稚樹の光環境と光合成生産（3）木部圧ポテンシャルの日変化

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プレッシャー・チェンバー法でS，I，O′区のシラベ稚樹の木部圧ポテンシャルの日変化を調べた。木部圧ポテンシャルの日変化には，樹冠の上下位置，方位による違いはなかった。木部圧ポテンシャルは，晴れ，曇りの日にはいずれの区でも－15bar前後まで低下したが，雨，霧の日には，夜間とほぼ同じ－2bar前後にしか低下しなかった。計測前の2時間の積算照度は，木部圧ポテンシャルの日変化に大きな影響をあたえていることがわかった。Diurnal fluctuations in xylem water potential of Abies veitchii LINDL. saplings were investigated in the plots S, I and O′ by the pressure chamber method on July 22 to 28 and August 17 to 21, 1980. Diurnal fluctuations in xylem water potential were not different at any positions or directions in a crown. In each plot, the xylem water potential decreased to -15 bar on fine or cloudy days, but to only -2 bar throughout the day on rainy or foggy days. The fluctuations in xylem water potential (XWP, bar) were closely related with the light intensity cumulated for 2 hours before the measurement of XWP (LC2, klx・hr・hr-1). The relations were represented by the following equations; Plot S: XWP=-1.25・LC2-2.0 Plot I: XWP=-0.22・LC2-1.5 Plot O′: XWP=-0.067・LC2-1.5