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

论文研究：与针叶树的抗栓塞性相关的结构-功能权衡，植物中的水运输可能会受到干旱和/或冰冻的挑战。 当受到任何一种现象时，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？ 本研究将通过对松科、柏科和罗汉松科植物的水力效率和木材解剖结构的研究来回答这一问题。 针叶树是这项研究的理想选择，因为其木材结构简单，加上其广泛的分布将允许有效的建模和测试其对干旱和冻结的水力响应。 目前，已知大的木质部导管是水的有效导体，但非常容易受到冷冻诱导的栓塞。 此外，耐旱木质部表现出高木材密度，并且建造成本高。 因此，导水率和木材密度分别代表与抗冻性和抗旱性相关的成本效益权衡的货币。 预测是，针叶树栖息在容易缺水和冻结的地区，如北美高沙漠，将不太容易受到这些压力，但在降低水力效率的代价，和高木材密度。 相反，生活在温暖的中温带地区的类群，在那里冰冻是罕见的，如在澳大利亚热带雨林，将表现出较低的耐旱性和冷冻应力，但将享受有效的水力传导。 最终，针叶树栖息在干旱冻结谱上的任何一点上，都会优化其成本效益策略，以最大限度地提高其栖息地的适应性。本研究的目的是澄清不仅在木质部解剖变异的生理意义，但也限制当前和过去的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.