Collaborative Research: Resistance, Repair and Redundancy: Traits that Protect Shrubs against Drought-induced Hydraulic Failure

在工程上，木本植物的液压系统是一个“负压流动系统”，在这个系统中，木材(木质部)中的传导细胞从根到叶连接在一起。这种类型的液压系统容易由于引入气泡而发生故障，从而产生栓子。植物的液压系统经常会发生堵塞，特别是在缺水的情况下。无论是人为的还是天然的，压力流量系统都可以通过三种方式来防止故障：阻力、可修复性和冗余性。植物对水力破坏的抵抗力是相当清楚的，它涉及到细胞壁、传导细胞和厚壁细胞(纤维)周围基质的厚度。失效后的修复能力取决于木质部内及其附近的活细胞。冗余度反映了根到叶传导途径的数量及其相互联系的程度(水力整合)。不同物种中传导细胞、支持纤维和活细胞的独特排列表明，这三种类型的保护之间存在权衡。到目前为止，它们之间的相互作用几乎是未知的。拟议的研究问题是，在北美、南美和澳大利亚的跨洲干旱梯度上，来自多个谱系的优势灌木物种的不同类型保护的相对量是否随着生境干旱的增加而变化。方法将涉及用于研究植物木质部结构的标准技术，以及使用染料示踪剂来表征水分运输的三维路径。木质部功能研究将量化对栓塞症的抵抗力和实验诱导的栓塞症的可修复性。这项研究将首次同时考察冗余、抗性和修复在保护植物免受水力破坏方面的相对作用。这项研究的结果将有助于研究人员和土地管理人员理解在全球气候变化和荒漠化期间，水力保护如何影响灌木生存。不同年龄、种族和文化背景的学生将在参与研究的各个方面体验科学过程。

In engineering terms, the hydraulic system of a woody plant is a "negative pressure flowsystem" in which conducting cells in the wood (xylem) are linked from roots to leaves.This type of hydraulic system is prone to failure due to the introduction of air bubbles,which create embolisms. Plants frequently develop embolisms in their hydraulic systems, especially under water limited conditions.Whether man-made or natural, a pressure flow system can be protected fromfailure in three ways: resistance, reparability, and redundancy. Resistance to hydraulicfailure in plants is fairly well understood and involves the thickness of cells walls inconducting cells and in the surrounding matrix of thick-walled cells (fibers). Reparabilityafter failure depends on living cells in and adjacent to xylem. Redundancy reflects thenumber of root to leaf conducing pathways and the degree of their interconnectedness(hydraulic integration). The unique arrangements of conducting cells, supporting fibers,and living cells in different species suggest that tradeoffs occur among these three types of protections. To date, interactions among them are virtually unknown.The proposed research questions whether the relative amounts of different typesof protection change with increasing habitat aridity in dominant shrub species frommultiple lineages along transcontinental aridity gradients in North America, SouthAmerica, and Australia. Methods will involve standard techniques used to study thestructure of plant xylem and the use of dye tracers to characterize three-dimensionalpathways of water transport. Xylem function studies will quantify resistance toembolisms and reparability of experimentally induced embolisms. This study will be thefirst to simultaneously examine the relative roles of redundancy, resistance and repair inprotecting plants from hydraulic failure.Results from this study will aid researchers and land managers in understandinghow hydraulic protection influences shrub survival during global climate change anddesertification. Students of different ages, ethnic, and cultural backgrounds willexperience the scientific process as they participate in every aspect of the research.