Scoffoni, Christine , Rawls, Micheal , McKown, Athena D. , Sack, Lawren .
Decline of leaf hydraulic conductance during desiccation: relationships to venation architecture.
Leaves greatly vary in their venation architecture among species. Veins play a major role in leaf support but also deliver water to mesophyll cells and make up for water lost during transpiration. Therefore, leaf hydraulic conductance (Kleaf), a measure of the capacity for water movement from petiole to leaf airspaces for transpiration, should be greatly influenced by venation architecture. We hypothesized that the drought sensitivity of Kleaf would also be related to venation architecture, because modeling and experimental work indicated that severing major veins would reduce overall Kleaf. We examined the relations between desiccation response curves and venation architecture in ten species varying strongly in drought tolerance. We developed a new method to measure the decline in Kleaf with water potential using the evaporative flux method, and quantified venation architecture, including densities of all vein orders, as well as pressure-volume curves and cuticular conductance (gmin). We investigated the decline of Kleaf with desiccation, testing multiple models within a maximum likelihood framework, and determined association of the responses with venation architecture and other aspects of leaf composition and function. We found species variation in the shape of the Kleaf response to desiccation, and difference in the best-fit model. We found very strong variation in the water potential at 50% loss of conductivity of Kleaf(PLC50) , an index of hydraulic sensitivity to desiccation. Across species, PLC50 was positively associated with major vein density, and with decreasing leaf size. This work provides new guidance for hydraulic measurement practices and provides a framework for future studies in unraveling the mechanisms involved in the decline of Kleaf during desiccation. The novel relationship between major vein density and PLC50 confirms theory that Kleaf is sensitive to major vein function. This association also points to new principles for understanding leaf function and evolution, indicating an inherent advantage in smaller leaves for tolerance of the hydraulic system to desiccation.
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1 - University of California, Los Angeles, Ecology and Evolutionary Biology, 621 Charles E. Young Drive, Los Angeles, CA, 90095, USA
turgor loss point
Presentation Type: Oral Paper:Papers for Topics
Location: 551B/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 8:45 AM