Bueno Amauri, Alonso-Forn David, Peguero-Pina José Javier, de Souza Aline Xavier, Ferrio Juan Pedro, Sancho-Knapik Domingo, Gil-Pelegrín Eustaquio
Chair of Botany II - Ecophysiology and Vegetation Ecology, Julius von Sachs Institute of Biological Sciences, University of Würzburg, Würzburg, Germany.
Unidad de Recursos Forestales, Centro de Investigación y Tecnología Agroalimentaria de Aragón, Zaragoza, Spain.
Front Plant Sci. 2022 Jan 24;12:786933. doi: 10.3389/fpls.2021.786933. eCollection 2021.
The search for a universal explanation of the altitudinal limit determined by the alpine treeline has given rise to different hypotheses. In this study, we revisited Michaelis' hypothesis which proposed that an inadequate "ripening" of the cuticle caused a greater transpiration rate during winter in the treeline. However, few studies with different explanations have investigated the role of passive mechanisms of needles for protecting against water loss during winter in conifers at the treeline. To shed light on this, the cuticular transpiration barrier was studied in the transition from subalpine forests to alpine tundra at the upper limit of the species in the Pyrenees. This upper limit of was selected here as an example of the ecotones formed by conifers in the temperate mountains of the northern hemisphere. Our study showed that minimum leaf conductance in needles from upper limit specimens was higher than those measured in specimens living in the lower levels of the sub-alpine forest and also displayed lower cuticle thickness values, which should reinforce the seminal hypothesis by Michaelis. Our study showed clear evidence that supports the inadequate development of needle cuticles as one of the factors that lead to increased transpirational water losses during winter and, consequently, a higher risk of suffering frost drought.
对由高山林线决定的海拔极限进行普遍解释的探索引发了不同的假说。在本研究中，我们重新审视了米夏埃利斯的假说，该假说认为角质层“成熟”不足导致林线树木在冬季的蒸腾速率更高。然而，很少有采用不同解释的研究调查针叶的被动机制在林线针叶树冬季防止水分流失方面的作用。为了阐明这一点，我们在比利牛斯山脉该物种上限处从亚高山森林向高山冻原的过渡地带研究了角质层蒸腾屏障。这里选择这个上限作为北半球温带山区针叶树形成的生态交错带的一个例子。我们的研究表明，上限标本针叶的最小叶片导度高于生活在亚高山森林较低层的标本，并且角质层厚度值也较低，这应该会强化米夏埃利斯的开创性假说。我们的研究显示了明确的证据，支持针叶角质层发育不足是导致冬季蒸腾水分损失增加的因素之一，因此遭受冻旱的风险更高。
