Defining plant hydraulic traits is central to the quantification of ecohydrological processes ranging from land‐atmosphere interactions, to tree mortality and water‐carbon budgets. A key plant trait is the xylem specific hydraulic conductivity (K_x), that describes the plant's vascular system capacity to transport water. While xylem's vessels and tracheids are dead upon maturity, the xylem is neither inert nor deadwood, various components of the sapwood and surrounding tissue remaining alive and functional. Moreover, the established definition of K_x assumes linear relations between water flux and pressure gradient by tacitly considering the xylem as a “passive conduit”. Here, we re‐examine this notion of an inert xylem by systematically characterizing xylem flow in several woody plants using K_x measurements under constant and cyclic pressure gradients. Results show a temporal and pressure gradient dependence of K_x. Additionally, microscopic features in “living branches” are irreversibly modified upon drying of the xylem, thus differentiating the macroscopic definition of K_x for living and dead xylem. The findings highlight the picture of the xylem as a complex and delicate conductive system whose hydraulic behaviour transcends a passive gradient‐based flow. The study sheds new light on xylem conceptualization, conductivity measurement protocols, in situ long‐distance water transport and ecosystem modelling.

中文翻译：

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新鲜木质部水力传导率的持续衰减随压力梯度而变化，并标记植物对伤害的反应。

定义植物水力性状是量化生态水文学过程的核心，生态水文学过程的范围从陆地-大气相互作用到树木死亡和水碳预算。关键的植物性状是木质部比水导率（K _x），它描述了植物的血管系统输送水的能力。尽管木质部的血管和气管在成熟时会死亡，但木质部既不是惰性的也不是枯木，边材和周围组织的各种成分仍然活着并起作用。此外，K _x的既定定义通过默认将木质部视为“被动导管”，假设水通量与压力梯度之间存在线性关系。在这里，我们通过在恒定和循环压力梯度下使用K _x测量系统地表征几种木本植物中木质部流动的方式，来重新研究惰性木质部的概念。结果表明，时间和压力梯度与K _x有关。另外，木质部干燥后，“活体分支”中的微观特征会不可逆地改变，从而区分了K _x的宏观定义。活生生的木质部。这些发现突出了木质部作为复杂而细腻的导电系统的图像，其水力行为超越了基于被动梯度的流动。这项研究为木质部概念化，电导率测量协议，原地长距离水运输和生态系统建模提供了新的思路。