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林业科学 ›› 2018, Vol. 54 ›› Issue (5): 143-151.doi: 10.11707/j.1001-7488.20180516

• 问题讨论 • 上一篇    下一篇

木本植物木质部栓塞测定技术的争议与进展

陈志成, 姜丽娜, 冯锦霞, 万贤崇   

  1. 中国林业科学研究院林业新技术研究所 北京 100091
  • 收稿日期:2017-11-20 修回日期:2018-01-05 出版日期:2018-05-25 发布日期:2018-06-05
  • 基金资助:
    中国林业科学研究院基本科研业务费专项资金项目(CAFYBB2017SY047);国家自然科学基金项目(31290223)。

Progress and Controversy of Xylem Embolism Determination Techniques in Woody Plants

Chen Zhicheng, Jiang Lina, Feng Jinxia, Wan Xianchong   

  1. Institute of Forestry New Technology, Chinese Academy of Forestry Beijing 100091
  • Received:2017-11-20 Revised:2018-01-05 Online:2018-05-25 Published:2018-06-05

摘要: 气候变化导致的全球尺度的森林衰败死亡增多,以植物水分关系为核心的树木死亡机制成为研究热点,而木本植物长距离水分运输中的木质部栓塞的研究是植物水分关系的核心。本文声学检测法、非破坏性成像技术和低压液流技术3类测定木质部栓塞的技术方法进行综述。声学检测法的优点是对植物材料无破坏性且具有较高的时间分辨率,但测定结果的可靠性差,这种方法更倾向于定性检测木质部栓塞。核磁共振和微CT成像技术是近年来兴起的非破坏性成像技术,对植物材料无破坏性,可对导管无偏差的三维成像;尤其是微CT技术,其空间分辨率小于1~2 μm,可更详尽地呈现出木质部的栓塞程度和分布模式以及栓塞形成和修复的动态。应用微CT方法是未来研究中的趋势,但此装置还不易获取,因此在当前的木质部栓塞研究中还难以广泛应用。低压液流方法是近30年来测定木质部栓塞应用最广泛的方法,本文对此方法的原理及操作步骤进行介绍。近年有学者提出在测定过程中可能会出现"张力-剪断假象",认为即使在水中剪断存在张力的枝条也会人为地增加所测样品的栓塞程度。这就质疑了之前树木栓塞日变化和栓塞修复的研究结果及用自然干燥法测定树木抗栓塞能力的研究结果。"张力-剪断假象"在植物水力研究领域引起激烈的讨论,之后有众多学者迅速设计针对性的试验开展研究,然而并没有重复出"张力-剪断假象",并且认为避免"张力-剪断假象"的张力释放过程发生了栓塞修复。"张力-剪断假象"虽然对低压液流方法测定木质部栓塞引起争议,但此事件使研究者认识到严格、细心地进行木质部栓塞测定操作的重要性。最后提出应用低压液流技术测定木质部栓塞操作中应该注意的10项建议。

关键词: 声学检测法, 核磁共振成像, 微CT, 低压液流, 张力-剪断假象, 栓塞修复

Abstract: In recent years, the forest decline and mortality on the global scale have been increasing because of climate change, which attracts a lot of researches on tree death mechanism involved in plant hydraulic structure. The xylem embolism in the long-distance water transport of woody plants is the key of plant water relations. This article reviews the three kinds of techniques for determination of xylem embolism, including acoustic detection, noninvasive imaging techniques and low pressure flow meter. The main advantages of acoustic detection are noninvasive for plant materials and have a very high temporal resolution, but the measured results are not so reliable. The acoustic method is more apt to qualitative detection of xylem embolism, and not easy for quantitative analysis of embolism. Nuclear magnetic resonance imaging technology and X-ray computed microtomography system (microCT) are noninvasive imaging techniques arisen in recent years. Those techniques facilitate unbiased three-dimensional observation of vessels. In particular, the microCT provides superior spatial resolution of less than 1-2 μm. Thus, microCT allows researchers to directly determine the degree of embolism, the spreading patterns of embolism, the dynamics of embolism formation and refilling in great detail. The application of microCT may be a trend in future studies, but the equipment is not readily available at the present, and therefore, it is difficult to be widely applied for the routine study of xylem embolisms. Low pressure flow meter is the most widely used method for determining xylem embolism in the past three decades. This article introduces the principle and operation procedure of this method. However, a recent study found a kind of "tension-cutting artifact" phenomenon, that is, cutting the tension branches even in water can artificially increase the degree of embolism of the measured samples. This finding had questioned the results of the previous studies on diurnal changes of embolism and embolism refilling, as well as the results of studies on evaluating species cavitation resistance based on bench dehydration with this method. The tension-cutting artifact caused heated discussions in the field of plant hydraulics, and many researches quickly designed the specific experiments to test the tension-cutting artifact. However, there was no repetition of "tension-cutting artifact", and conversely the embolization repair was found in the process of releasing tension for avoiding tension-cutting artifact. Although the tension-cutting artifact does not really exist in the xylem embolization determination by the low pressure flow meter, this event has led researchers to recognize the importance of strict and careful measurement operation of xylem embolization. Finally, this paper proposes ten suggestions for the measurement of xylem embolization using low pressure flow meter.

Key words: acoustic detection, magnetic resonance imaging, microCT, low pressure flow meter, tension-cutting artifact, embolism refilling

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