Levionnois Sébastien, Ziegler Camille, Jansen Steven, Calvet Emma, Coste Sabrina, Stahl Clément, Salmon Camille, Delzon Sylvain, Guichard Charlotte, Heuret Patrick
UMR EcoFoG, AgroParisTech, CIRAD, CNRS, INRAE, Université des Antilles, Université de Guyane, Kourou, 97310, France.
AMAP , Univ Montpellier , CIRAD, CNRS, INRAE, IRD, Montpellier, 34000, France.
New Phytol. 2020 Oct;228(2):512-524. doi: 10.1111/nph.16723. Epub 2020 Jul 3.
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.
茎叶过渡处的水力分割预示着叶片的水力阻力高于茎部。然而，脆弱性分割预示着叶片的抗栓塞能力较低。从理论上讲，这两种机制都应有利于叶片中的栓塞失控，以保护诸如茎等昂贵的器官，并且应对任何潜在的协调性进行测试。我们基于解剖学方法研究了理论上的叶片特定传导率，以量化21种热带雨林树种的水力分割程度。对茎（流动离心技术）和叶（光学可视化方法）中木质部对栓塞的抗性进行了量化，以评估脆弱性分割。我们发现物种间普遍存在水力分割，但分割程度差异很大。尽管脆弱性分割程度存在明显的连续性，但有8个物种表现出正的脆弱性分割（叶片比茎对栓塞的抗性更低），而其余研究的物种则表现出负的或无脆弱性分割。脆弱性分割程度与水力分割程度呈正相关，因此，具有分割的物种促进了两种将叶片木质部与茎木质部水力解耦的机制。水力和脆弱性分割在多大程度上决定抗旱性，需要在全株水平上进一步整合茎叶过渡，包括木质部和外部木质部组织。
