Study of the tolerance for low temperature of woody plants

在温带常绿树种中，从秋季到冬季，枝条膨压损失点和饱满膨压时渗透势的降低是众所周知的。这些水分关系的变化与冬小麦对低温和霜冻的耐受性密切相关。通过对柳杉幼苗根部和地上部温度的调控，验证了地上部水分关系的这种季节性变化是由根温驱动的假说。在田间条件下，当温度低于5℃时，地上部膨胀力损失点的下降更加明显。这种地上部水分关系的变化可能是对低温下增加的根系水力阻力的适应性反应，当水的粘度增加时。根的降温促进膨压损失点的降低，而根温的降低则延缓了膨压损失点的下降。但在冬季根温较低(&lt；5℃)的条件下，增温对地上部水分关系没有影响。根部降温引起的地上部水分关系的变化需要1周左右的时间，苗木或根部升温可逆转这种变化。膨压损失点的降低更多地是由细胞壁弹性的增加驱动的，而不是由渗透调节(如增加含糖量)驱动的。根据这些结果，我们阐明了秋冬季地上部水分关系的变化是对根(土)温降低的响应和对冬季寒冷的适应性反应。认为秋末春初柳杉冻害发生在地温高于5℃的条件下。

In temperate evergreen tree species, lowering of the turgor loss point of shoot and of the osmotic potential at full turgor from autumn into winter have been well known. These changes in shoot water relations closely relate to the tolerance to low temperature and frost in winter. We tested a hypothesis that such seasonal change in shoot water relations is driven by root temperature by manipulating temperature of root and shoot of Cryptomeria japonica seedlings separately. In field condition, the lowering of the turgor loss point of shoot becomes clear when the temperature was under 5℃. This change in shoot water relations might represent adaptive responses to increased root hydraulic resistance at low temperature, when the viscosity of water was increased. The lowering of the turgor loss point was accelerated by root cooling and delayed by root warming. However, shoot warming did not give any effect on the shoot water relations under the low root temperature (<5℃) in winter. The change in shoot water relations by root cooling needed about 1 week and was reversible by warming of the seedling or the root. The lowering of the turgor loss point was driven much more by the increasing in cell wall elasticity than by the osmotic adjustment such as increase in sugar content. From these results, we clarified that the changes in the shoot water relations from autumn to winter was the response to the decrease of root (soil) temperature and the adaptive response to the winter cold. It was considered that frost injury of Cryptomeria japonica in late autumn and early spring was occurred under the condition when soil temperature was higher than 5℃.