Water transport in vascular plants represents a critical component of terrestrial water cycles and supplies the water needed for the exchange of CO2 in the atmosphere for photosynthesis. Yet, many fundamental principles of water transport are difficult to assess given the scale and location of plant xylem. Here we review the mechanistic principles that underpin long-distance water transport in vascular plants, with a focus on woody species. We also discuss the recent development of noninvasive tools to study the functional status of xylem networks in planta. Limitations of current methods to detect drought-induced xylem blockages (e.g., embolisms) and quantify corresponding declines in sap flow, and the coordination of hydraulic dysfunction with other physiological processes are assessed. Future avenues of research focused on cross-validation of plant hydraulics methods are discussed, as well as a proposed fundamental shift in the theory and methodology used to characterize and measure plant water use.

中文翻译：

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木质部随时间的功能状态

维管植物中的水运输是陆地水循环的重要组成部分，并提供大气中二氧化碳交换进行光合作用所需的水。然而，鉴于植物木质部的规模和位置，水运的许多基本原理难以评估。在这里，我们回顾了支持维管植物长距离水运输的机械原理，重点是木本植物。我们还讨论了研究植物木质部网络功能状态的非侵入性工具的最新发展。评估了当前检测干旱引起的木质部阻塞（例如栓塞）和量化树液流量相应下降的方法的局限性，并评估了水力功能障碍与其他生理过程的协调。