低温环境下木材细胞中冰晶的形成和传播研究综述

活立木树干内部水分状态对其生理作用的发挥具有重要的影响。低温下,活立木内部水分状态的改变,导致其结构发生变化,这给基于声波技术的活立木材质无损检测带来了一些困难。笔者从宏观和微观角度,综述了树干和木质细胞中冰晶的形成、传播、分布和冰晶体含量的最新研究结果; 讨论了木材细胞内和细胞外水分的冻结模式和冻结行为; 介绍了时域反射技术、低温扫描电镜、差热分析、核磁共振等研究木材内部水冻结过程的方法并比较了各方法的特点。认为当前研究在技术手段、研究对象和深度上仍需进一步拓展,未来应重点以活立木树干及枝干为对象,利用多种手段加强原位检测,对冰晶形成原因、扩展过程及产生结果进行系统研究。通过对低温木材中冰晶的形成和传播机制的综合分析,可为后续开展低温活立木无损检测和树木抗寒性研究提供参考。
The state of the internal water in tree xylem is important in tree physiology and has a crucial effect on the quality of standing trees. However, there are several difficulties involved in the accurate and nondestructive evaluation of internal water using acoustic techniques, especially in winter. We reviewed the recent research about ice formation, propagation, distribution and crystal content, which reported both macroscopic tree stem and microscopic wood cell results. The freezing patterns and behavior of intracellular or extracellular water in woody tissue were also discussed. Several methods, including time domain reflectometry, cryo-scanning electron microscopy, differential thermal analysis and nuclear magnetic resonance, were used to study the freezing process of the internal water in wood, and their advantages were compared. Consider that further research is required to develop the technical methods, research objects and depth of analysis. In future, more in-situ detection should be performed on living standing tree trunks and branches using a variety of means to systematically study ice formation and expansion processes. A future aim would be to obtain a clear understanding of the mechanism of ice formation and propagation in wood at subzero temperatures