• 问题讨论 •

### 木本植物木质部栓塞测定技术的争议与进展

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

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.