林火干扰下的树木生理及主要影响因素

Tree physiology and major influencing factors under forest fires

随着全球逐渐暖干化,林火不仅驱动着森林生态系统结构和功能的变化,同时也影响树木的生理和生长。林火导致的热损伤引发树木一系列复杂生理响应。揭示火后树木生理的响应机制,对于进一步理解树木碳水关系和火后恢复生长限制,以及提高火后树木死亡预测准确性具有重要指导意义。该文从林火对树木的作用途径和方式着手,基于不同形式林火(树冠火、地表火、地下火)对树木各部分(树冠、树干、根系)造成的损伤,综述了林火对树木生理的直接影响和间接影响,以及火后树木生理与非生物和生物因素的互作关系。热损伤诱导的形成层、韧皮部坏死和木质部水力失衡是火后树木生理的主要响应机制,二者导致的两个生理功能限制“碳饥饿”和水力失效严重影响树木的碳水关系,也决定了火后树木是恢复生长还是延迟死亡。火后树木生理机制还与干旱、昆虫攻击和微生物入侵等其他因素密切相关。该文强调了对林火强度的定量分析和对植物组织死亡阈值的准确判断的迫切性,同时提出了探究火后树木生理与功能性状和其他因素的互作关系的必要性。精确评估树木生理机制间关系对于深入理解林火如何影响树木功能完整性极为关键,有助于完善林火风险评估和树木死亡模型预测。在未来气候暖干化驱动的高频、高强度林火发生背景下,对树木生理响应的深刻认识对于更好地研究火后生态系统动态及其与气候因子的相互关系同样具有重要意义。

With gradual global warming and drying up,forest fires not only drive changes in the structure and function of forest ecosystems,but also affect the physiology and growth of trees.The thermal damage caused by forest fires can trigger a series of complicated physiological responses in trees.Revealing the response mechanisms of postfire tree physiology can guide the further understanding of the carbon-water relationship and how it influences the postfire growth recovery limitations of trees.Furthermore,the accuracy of tree mortality prediction after fires must be improved.Starting with a description of the pathways in which forest fires affect trees,this review elaborates on the damage caused by different forms of forest fires(canopy,surface,and ground fires)on various parts(crowns,trunks,and roots)of trees.In particular,this review discusses the direct and indirect effects of forest fires on tree physiology and the tree physiology-abiotic/biotic interactions after fires.Cambium and phloem necrosis and xylem hydraulic dysfunction are the main response mechanisms of postfire tree physiology.The two physiological functional limitations—carbon starvation and hydraulic failure—caused by the two aforementioned mechanisms seriously affect the carbon-water relationship of trees,further influencing the growth recovery of trees or their delayed death after fires.The physiological mechanisms of trees after fires are also closely related to drought,insect attack,microbial invasion,and other factors.The quantitative analyses of forest fire intensity and the accurate judgment of the plant tissue death threshold are urgent tasks,and the interaction of tree physiology with the functional traits of trees and other factors after fires must be explored.Accurately evaluating the relationship between tree physiological mechanisms is crucial in fully understanding how forest fires affect the tree functional integrity of trees and contributes to the improvement of forest fire risk assessments and mortality model predictions.In the context of high-frequency and high-intensity forest fires driven by future climate warming and drying,a profound understanding of tree physiological responses can also enhance the study of the dynamics of postfire ecosystems and their interrelationships with climate factors.