Principles of leaf hydraulic design

树叶是平衡二氧化碳吸收和水分流失的复杂结构。这项工作致力于研究叶片的微观水文学，重点关注两个目标：(1)了解叶片内水分运动的生物物理；(2)确定将光合作用细胞从蒸腾作用所带来的高水分需求中分离出来的生理意义。早期的研究表明，树叶由两个水力隔离的水池组成，通过低阻力和高阻力途径与供水途径(木质部)相连。这些水力上不同的水池如何与树叶的结构和生理相关尚不清楚。一种假设是，光合作用细胞通过水力方式与蒸腾作用流隔离，这种隔离受到生物控制。蒸腾路径与光合作用组织的分离可能会保护携带叶绿素的细胞免受微环境条件突然变化的影响。其目的是了解叶片水力设计的原理，探索叶片水力分区的生物学基础，并确定叶片内部水力结构的生理意义。这项研究将包括对树叶的再水化动力学进行分析，以量化两个隔室的相对大小。此外，细胞压力探头测量将确定不同“隔室”之间的液压连接以及这些池的身份。这些方法将与实验处理(温度、代谢抑制剂)和形态研究相结合，以解决两个水池水力分离的性质。数学模型将被用来探索划分对叶片性能影响的方式。将测量气孔行为和木质部脆弱性，以确定是否存在快速水力隔室，使植物能够在接近空化极限的情况下运行。这项研究将从根本上改变人们对叶片结构和生理的理解。此外，这项研究将通过将叶水区划的研究扩展到代表不同进化谱系、生长形式和生态的广泛分类群来提高对植物多样性的理解。导致更广泛影响的活动旨在将本研究的想法扩展到更广泛的受众。这些活动包括：(1)指导和支持各级青年科学家；(2)面向公众的外联活动。工作将包括创建和维护一个关于树叶液压的网页，该网页链接到阿诺德植物园的网站。该网站将解释这项研究的目标和目前的发现，并将为参观植物园的学校班级概述与此主题相关的活动。此外，这项研究将通过在阿诺德植物园的公开讲座来普及，作为他们正在进行的公共计划的一部分，并在Arnoldia杂志上发表一篇文章。

Leaves are complex structures that balance CO2 uptake and water loss. This work addresses the micro-hydrology of leaves, focusing on two goals: (1) understand the biophysics of water movement within leaves and (2) determine the physiological significance of separating photosynthetic cells from the high demands for water imposed by the transpiration. Earlier studies show that leaves consist of two hydraulically isolated water pools linked to the water supply path (xylem) via low and high resistance pathways. How these hydraulically distinct pools of water are related to the structure and physiology of leaves is not known. One hypothesis is that photosynthetic cells are hydraulically isolated from the transpiration stream and that this isolation is under biological control. The separation of the transpirational path from the photosynthetic tissue may protect chlorophyll bearing cells from sudden changes in micro-environmental conditions. The goals are to understand the principles of leaf hydraulic design, explore the biological basis for hydraulic compartmentalization, and determine the physiological significance of the internal hydraulic architecture of leaves. The research will include analysis of rehydration kinetics of leaves to quantify the relative sizes of the two compartments. In addition, cell pressure probe measurements will determine hydraulic linkages between different "compartments" as well as the identity of these pools. These methods will be combined with experimental treatments (temperature, metabolic inhibitors) and morphological studies to resolve the nature of the hydraulic separation of the two water pools. Mathematical modeling will be used to explore the ways in which compartmentalization impacts leaf performance. Stomatal behavior and xylem vulnerability will be measured to determine whether a fast hydraulic compartment exists that allows plants to operate close to their cavitation limit. The research will fundamentally alter the understanding of the structure and physiology of leaves. In addition, the research will improve understanding of plant diversity by extending the studies of foliar water compartmentalization across a wide range of taxa representing diverse evolutionary lineages, growth forms, and ecologies. Activities leading to broader impacts are designed to extend ideas from this research to a broader audience. Such activities include: (1) mentoring and supporting younger scientists at all levels and (2) outreach activities directed to the public. Efforts will include creation and maintenance of a webpage on leaf hydraulics that is linked to the Arnold Arboretum website. The website will explain the goals and current findings of this research and will outline activities relevant to this topic for school classes visiting the Arboretum. In addition this research will be popularized via public lectures at The Arnold Arboretum as a part of their ongoing public program and an article in Arnoldia magazine.