DISSERTATION RESEARCH: The structure-function tradeoffs associated with embolism resistance in conifer wood

论文研究：与针叶树木材抗栓塞性相关的结构-功能权衡john Sperry和Jarmila pittermanu犹他大学植物的水分运输可能受到干旱和/或冻结的挑战。当发生任何一种现象时，空气进入导水组织（木质部）可能会损害水从根到茎的运动，这通常被称为栓塞。在这些压力下，与抗栓塞相关的成本是什么？目前的研究将通过调查松科、柏科和足足科成员的水力效率和木材解剖来回答这个问题。针叶树是这项研究的理想选择，因为它们的木材结构简单，再加上它们广泛的分布，将允许有效的建模和测试它们对干旱和冻结的水力反应。目前，已知大木质部导管是水的有效导体，但极易受到冰冻引起的栓塞。此外，抗旱木质部表现出高木材密度，并且建造成本高。因此，水力导度和木材密度分别代表了与抗冻性和抗旱性相关的成本效益权衡的货币。据预测，居住在容易缺水和结冰地区的针叶树，如北美高原沙漠，将不那么容易受到这些压力的影响，但代价是水力效率降低，木材密度高。相反，生活在温暖、潮湿、很少发生冰冻的地区的类群，如澳大利亚的热带雨林，对干旱和冰冻胁迫的耐受性较低，但会享受有效的水力传导。最终，居住在干旱-冰冻光谱上任何一点的针叶树将优化其成本-收益策略，以最大化其栖息地的适应性。本研究的目的不仅是阐明木质部解剖结构变异的生理意义，而且是限制现在和过去针叶树分布的选择力。

Dissertation Research: The structure-function tradeoffs associated with embolism resistance in conifer woodJohn Sperry and Jarmila PittermannUniversity of UtahWater transport in plants may be challenged by drought and/or freezing. When subjected to either phenomenon, the introduction of air into the water conducting tissue (xylem) may impair the movement of water from root to stem by what is commonly referred to as embolism. What are the costs associated with resistance to embolism under these stresses? The current research will answer this question by investigating the hydraulic efficiency and wood anatomy of members of the Pinaceae, Cupressaceae and Podocarpaceae families. Conifers are the ideal choice for this study because the structural simplicity of their wood, coupled with their broad distribution will allow for effective modeling and testing of their hydraulic response to drought and freezing. Currently, it is known that large xylem conduits are efficient conductors of water, but highly vulnerable to freezing-induced embolism. Also, drought resistant xylem exhibits high wood density, and is costly to construct. Hence, hydraulic conductance and wood density represent the currency of the cost-benefit tradeoffs associated with freezing and drought resistance, respectively. The predictions are that conifers inhabiting regions prone to water deficit and freezing, such as North American high deserts, will be much less vulnerable to these stresses, but at the cost of reduced hydraulic efficiency, and high wood density. Conversely, taxa inhabiting warm, mesic regions where freezing is rare, as in Australian tropical rainforests, will exhibit low tolerance to drought and freezing stress, but will enjoy efficient hydraulic conductance. Ultimately, conifers inhabiting any point on the drought-freezing spectrum will optimize their cost-benefit strategy to maximize fitness in their habitat. The goals of this research are to clarify not only the physiological significance of variation in xylem anatomy, but also the selective forces restricting current and past conifer distributions.