Collaborative Research: Resistance, Repair and Redundancy: Traits that protect shrubs against drought-induced hydraulic failure

在工程术语中，木本植物的液压系统是一个“负压流动系统”，其中木材（木质部）中的传导细胞从根连接到叶。这种类型的液压系统容易因引入气泡而发生故障，从而产生栓塞。植物的液压系统经常发生栓塞，特别是在水有限的条件下。无论是人为的还是自然的，压力流系统都可以通过三种方式避免故障：阻力、可修复性和冗余。植物对水力破坏的抵抗力是相当清楚的，它涉及到传导细胞和周围厚壁细胞（纤维）基质的细胞壁厚度。故障后的修复能力取决于木质部内和木质部附近的活细胞。冗余反映了根到叶传导途径的数量及其相互联系的程度（水力集成）。不同物种中传导细胞、支撑纤维和活细胞的独特排列表明，这三种保护类型之间存在权衡。迄今为止，它们之间的相互作用实际上是未知的。本研究提出的问题是，在北美、南美和澳大利亚沿横贯大陆干旱梯度的多系优势灌木物种中，不同类型保护的相对数量是否会随着栖息地干旱程度的增加而变化。方法将包括用于研究植物木质部结构的标准技术和使用染料示踪剂来表征水运输的三维途径。木质部功能的研究将量化对栓塞的抗性和实验性诱导栓塞的可修复性。这项研究将是第一次同时研究冗余、阻力和修复在保护植物免受水力破坏中的相对作用。这项研究的结果将有助于研究人员和土地管理者了解在全球气候变化和荒漠化的情况下，水力保护如何影响灌木的生存。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时体验科学过程。

In engineering terms, the hydraulic system of a woody plant is a "negative pressure flow system" 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 from failure in three ways: resistance, reparability, and redundancy. Resistance to hydraulic failure in plants is fairly well understood and involves the thickness of cells walls in conducting cells and in the surrounding matrix of thick-walled cells (fibers). Reparability after failure depends on living cells in and adjacent to xylem. Redundancy reflects the number 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 types of protection change with increasing habitat aridity in dominant shrub species from multiple lineages along transcontinental aridity gradients in North America, South America, and Australia. Methods will involve standard techniques used to study the structure of plant xylem and the use of dye tracers to characterize three-dimensional pathways of water transport. Xylem function studies will quantify resistance to embolisms and reparability of experimentally induced embolisms. This study will be the first to simultaneously examine the relative roles of redundancy, resistance and repair in protecting plants from hydraulic failure. Results from this study will aid researchers and land managers in understanding how hydraulic protection influences shrub survival during global climate change and desertification. Students of different ages, ethnic, and cultural backgrounds will experience the scientific process as they participate in every aspect of the research.