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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。
Living wood trunk moisture status of its physiological role play an important impact. Under low temperature, the change of internal moisture state of living wood leads to the change of its structure, which brings some difficulties to nondestructive testing of living wood based on acoustic wave technology. The author summarizes the latest research results on the formation, propagation, distribution and ice crystal content of ice crystals in trunk and lignocelluloses from the macroscopic and microscopic perspectives. The freezing modes and freezing behaviors of intracellular and extracellular water are discussed. Reflection technique, low-temperature scanning electron microscopy, differential thermal analysis, nuclear magnetic resonance and other methods to study the internal water freezing process of wood and compare the characteristics of each method. It is believed that the current research needs to be further expanded in terms of technical means, research objects and depth. In the future, the focus should be on live tree trunks and branches, and various measures should be taken to strengthen the in situ detection. The reasons for the formation of ice crystals, the expansion process and the production results system Research. Through the comprehensive analysis of ice crystal formation and transmission mechanism in low temperature wood, it can provide reference for the follow-up research on non-destructive testing of low temperature living trees and cold hardiness of trees.