Comparative Analysis of Xylem Function

植物木质部，或木材，是陆地上最丰富的组织。在所有的血管组织中，它携带的液体最多--水--距离最远。它的功能影响从光合作用、土壤呼吸到天气的方方面面。这项研究集中在木材功能的两个关键属性：维持负水压力而不对汽相产生空化，以及保持最小的流动摩擦阻力。这些特性影响植物的抗逆性和生产力。气蚀是由管道之间的阀状“凹坑”失效引起的。这项研究将检验基于概率的假设，即每条管道的凹坑数量增加时，空化的脆弱性也会增加。测试将包括空气注入实验和核磁共振成像(MRI)，以观察完好无损的树木内的血管系统。“自然实验”将把开花植物与更古老的植物类群--绞股蓝--进行比较，它们是具有不同坑道结构的不同谱系。该研究还将评估穿孔板对流动阻力的贡献，穿孔板是管道元件之间的连接。这些节点已经从高阻、坑坑洼洼的端壁发展到与管道一样宽的开口。这种形态梯度的功能特性将在开花植物和裸子植物的平行谱系中得到记录。单管道测量和有限元建模将把接头结构与流动阻力联系起来。这项研究的结果将填补我们对木材结构的知识和植物在自然和栽培环境中的表现之间的巨大差距。在这项研究的更广泛影响中，将开发图像分析软件，用于从木材的微观图像快速推断功能特性。这一“结构-功能”指数将向教育工作者和研究人员免费提供。这对于从世界各地机构保存的大量木材(包括化石)中提取功能数据至关重要。该项目还将涉及本科生和研究生以及博士后助理的培训。

Plant xylem, or wood, is the most abundant tissue on land. Of all vascular tissues, it carries the most fluid - water - the longest distances. How it functions influences everything from photosynthesis and soil respiration to the weather. This research focuses on two key properties of wood function: sustaining negative water pressure without cavitating to the vapor phase, and maintaining minimal frictional resistance to flow. These properties influence plant stress tolerance and productivity. Cavitation is caused by failure of valve-like "pits" between conduits. The research will test the probability-based hypothesis that the vulnerability to cavitation increases as the number of pits per conduit increases. Tests will involve air-injection experiments and Magnetic Resonance Imaging (MRI) to view vasculature inside intact trees. "Natural experiments" will compare flowering plants with the more ancient plant group, Gnetophytes, separate lineages with distinct pit structure. The research will also evaluate the contribution of perforation plates, the joints between conduit elements, to flow resistance. These joints have evolved from high-resistance, pitted end-walls, to openings as wide as the conduit. The functional properties of this morphological gradient will be documented in parallel lineages of flowering plants and Gnetophytes. Single-conduit measurements and finite-element modeling will link joint structure to flow resistance. Results of this research will fill the sizable gap between our knowledge of wood structure and the performance of plants in their natural and cultivated environments. Among the broader impacts of this research will be the development of image-analysis software for rapid inference of functional properties from microscopic images of wood. This "structure-function" index will be freely available to educators and researchers. It will be essential for extracting functional data from extensive collections of wood, including fossils, held in institutions around the world. The project will also involve training of undergraduate and graduate students as well as post-doctoral associates.