北海道の厳冬期におけるニオイヒバの葉の水分特性と生育環境の関係

抄録

Tissue water relations of Thuja occidentalis L. leaves under three different sets of environmental conditions, that is, sunlit and not covered with snow-leaves (sunlit leaves), shaded and not covered with snow-leaves (shaded leaves), and shaded and covered with snow-leaves, were measured in winter using the pressure-volume technique. Daily maximum and minimum temperatures in the sunlit leaves were 2 to 3°C and -26°C, respectively, whereas, they were -7 to -11°C and -22 to -24°C, respectively, in the shaded leaves and in the shaded and covered with snow-leaves. This showed that the sunlit leaves were exposed to severer temperature conditions. There was no significant differences in the water deficits at turgor losses among the three kinds of leaves. Both the osmotic potential at turgor loss and the osmotic potential at full turgidity were significantly lower in the sunlit leaves than in the shaded leaves, and the shaded and covered with snow-leaves. This result seemed to indicate that the sunlit leaves had higher tugor maintenance capacity due to osmotic adjustment during water stress resulting from dehydration by extracellular freezing and transpiration. The lower osmotic potential in the sunlit leaves resulted from the significantly greater number of osmoles per unit of dry weight. The significantly greater values of the bulk modulus of elasticity in the sunlit leaves seemed to show that the leaf cells of the sunlit leaves were stronger mechanically than those of the shaded leaves, and those of the shaded and covered with snow-leaves.