Comparative Analysis of Xylem Function

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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.