Collaborative Research: Resistance, Repair and Redundancy: Traits that Protect Shrubs against Drought-induced Hydraulic Failure

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In engineering terms, the hydraulic system of a woody plant is a "negative pressure flowsystem" 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 fromfailure in three ways: resistance, reparability, and redundancy. Resistance to hydraulicfailure in plants is fairly well understood and involves the thickness of cells walls inconducting cells and in the surrounding matrix of thick-walled cells (fibers). Reparabilityafter failure depends on living cells in and adjacent to xylem. Redundancy reflects thenumber 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 typesof protection change with increasing habitat aridity in dominant shrub species frommultiple lineages along transcontinental aridity gradients in North America, SouthAmerica, and Australia. Methods will involve standard techniques used to study thestructure of plant xylem and the use of dye tracers to characterize three-dimensionalpathways of water transport. Xylem function studies will quantify resistance toembolisms and reparability of experimentally induced embolisms. This study will be thefirst to simultaneously examine the relative roles of redundancy, resistance and repair inprotecting plants from hydraulic failure.Results from this study will aid researchers and land managers in understandinghow hydraulic protection influences shrub survival during global climate change anddesertification. Students of different ages, ethnic, and cultural backgrounds willexperience the scientific process as they participate in every aspect of the research.