Collaborative Research: Comparative Hydraulic Architecture; An Analysis of Transport Efficiency and Mechanical Constraints

植物需要通过光合作用来获取二氧化碳，这导致了叶片中大量水蒸气的被动损失，这些水蒸气必须不断地被木质部所取代。木质部是一种运输组织，由数千个从根到叶的死的中空管道组成。水力结构决定了木质部向叶片供水的能力和效率，从而限制了植物获得碳和生长的速度。在许多木本植物中，木质部导管具有输水和机械支撑的双重功能，导致为了机械稳定性而牺牲部分水力效率。本研究的目的是通过评估木质部水力与机械功能的权衡程度，对主要植物类群和生长形式的水力结构多样性进行分类和理解。这将通过确定几个关键的维管网络特征，如水力导电性，导管数量和面积，以及水运输速度从植物基部到其最上层分支的变化来完成。这些结果将绘制在图形上以生成水力景观。不同植物类型在这些景观中的位置将表明木质部的机械支撑功能对其水力功能的限制程度。棕榈树和藤蔓被认为比树木更具水力效率，因为与树木不同，它们的木质部只运输水而不提供结构支撑。在温带树木中，水力效率与木质部导管相对于其他细胞类型的木材比例呈负相关。最后，冻结对木质部结构施加的限制应使温带树木的水力效率低于热带树木。这项研究将增进对森林和其他自然和管理的生态系统的生长和生产力的内在限制的了解。这项工作的更广泛影响包括为博士后科学家、本科生和研究生以及将参加史密森热带研究所在巴拿马开展的工作的拉丁美洲学生提供培训和指导机会。

The need for plants to acquire CO2 for photosynthesis results in the passive loss of large amounts of water vapor from their leaves, which must be continuously replaced by the xylem, a transport tissue consisting of thousands of dead, hollow conduits running from the roots to the leaves. Hydraulic architecture determines the capacity and efficiency with which the xylem is able to supply water to the leaves, and thus limits the rate at which plants can gain carbon and grow. In many woody plants, the xylem conduits serve dual functions of water transport and mechanical support, leading to a partial sacrifice of hydraulic efficiency for mechanical stability. The goals of this research are to classify and understand the diversity of hydraulic architecture across major plant groups and growth forms by evaluating the extent of trade-offs of hydraulic against mechanical functions of xylem. This will be accomplished by determining how several key vascular network traits such as hydraulic conductivity, conduit number and area, and water transport velocity change from near the base of the plant to its uppermost branches. These results will be plotted on graphs to generate hydraulic landscapes. The positions of different plant types on these landscapes will indicate the extent to which the mechanical support function of xylem constrains its hydraulic function. Palms and vines are expected to be more hydraulically efficient than trees because, unlike trees, their xylem only transports water and does not provide structural support. Within temperate trees, a negative relationship between hydraulic efficiency and the proportion of wood devoted to xylem conduits relative to other cell types is expected. Finally, restrictions on xylem structure imposed by freezing should make temperate trees less hydraulically efficient than tropical trees. This research will enhance understanding of intrinsic constraints on the growth and productivity of forests and other natural and managed ecosystems. Broader impacts of this work include training and mentoring opportunities for a postdoctoral scientist, undergraduate and graduate students, was well as for Latin American students who will participate in the work to be carried out in Panama at the Smithsonian Tropical Research Institute.