• Hydraulic segmentation at the stem–leaf transition predicts higher hydraulic resistance in leaves than in stems. Vulnerability segmentation, however, predicts lower embolism resistance in leaves. Both mechanisms should theoretically favour runaway embolism in leaves to preserve expensive organs such as stems, and should be tested for any potential coordination.
• We investigated the theoretical leaf‐specific conductivity based on an anatomical approach to quantify the degree of hydraulic segmentation across 21 tropical rainforest tree species. Xylem resistance to embolism in stems (flow‐centrifugation technique) and leaves (optical visualization method) was quantified to assess vulnerability segmentation.
• We found a pervasive hydraulic segmentation across species, but with a strong variability in the degree of segmentation. Despite a clear continuum in the degree of vulnerability segmentation, eight species showed a positive vulnerability segmentation (leaves less resistant to embolism than stems), whereas the remaining species studied exhibited a negative or no vulnerability segmentation.
• The degree of vulnerability segmentation was positively related to the degree of hydraulic segmentation, such that segmented species promote both mechanisms to hydraulically decouple leaf xylem from stem xylem. To what extent hydraulic and vulnerability segmentation determine drought resistance requires further integration of the leaf–stem transition at the whole‐plant level, including both xylem and outer xylem tissue.

中文翻译：

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茎叶过渡期的脆弱性和水力分割：新热带树木之间的协调。

• 茎-叶过渡处的水力分段预测叶片中的水力阻力高于茎中的水力阻力。但是，脆弱性细分可以预测叶片中较低的抗栓塞性。从理论上讲，这两种机制均应支持叶片失控栓塞，以保护昂贵的器官（例如茎），并应进行任何潜在的配合测试。
• 我们研究了基于解剖学方法的理论叶比电导率，以量化21种热带雨林树种的水力分割程度。木质部对茎（流动离心技术）和叶片（光学可视化方法）对栓塞的抵抗力被量化以评估脆弱性分割。
• 我们发现了跨物种的普遍水力分割，但是分割程度存在很大的差异。尽管在脆弱性分割程度上有明显的连续性，但有八个物种显示出正性的脆弱性分割（对栓塞的抵抗力比茎低），而其余研究物种则显示出负性或没有脆弱性分割。
• 脆弱性分割的程度与水力分割的程度呈正相关，因此被分割的物种促进了两种机制来将叶木质部与茎部木质部水力分离。水力和脆弱性分段在多大程度上确定了抗旱性，需要在整个植物水平上（包括木质部和外部木质部组织）进一步整合叶-茎过渡。