Christman, Maggie A. , Sperry, John S. .
Single-vessel flow measurements indicate scalariform plates confer higher flow resistance than previously estimated.
During vessel evolution in angiosperms, the number of openings in perforation plates has tended to decrease from many-barred scalariform plates to single-opening simple plates. This transition is thought to have been accompanied by a decrease in hydraulic resistance to water flow through the vessel. Previously, the added resistance presented by scalariform plates has been estimated to be small - only about 10% or less based on numerical and large-scale physical models. Here, using the single vessel technique, we directly measured the hydraulic resistance of individual vessel lumens with scalariform or simple plates in order to assess how much resistance a scalariform plate confers and how plate structure affects resistance. Simple plated species had individual vessel resistivities which agreed well with predictions based on vessel diameter using the Hagen-Poiseuille equation (3.9% mean deviation). Across 14 scalariform plated species measured, lumen resistivity averaged 125.3% higher than predicted from vessel diameters using a regression from simple plated species. Perforation plate resistance (rplate) ranged widely (19.6-84.9%) and averaged 55.5% of the total resistance of each vessel element. Plate angle (relative to the elementís axis), plate length, distance between bars, and number of bars per plate were all tightly correlated with each other. Thus, long scalariform plates were typically of low angle with many closely-spaced bars, and vice versa. Scalariform rplate was tightly correlated with plate angle, length, and number of bars per plate, such that long, low angle, many-barred plates had the greatest rplate. Plates with very high resistance also tended to be spaced farther apart. Surprisingly, bar thickness increased with distance between bars, so that apparently more derived plates have thicker bars compared to the ancestral bar thickness. In summary, our results indicate that scalariform plates present a substantial impediment to hydraulic water flow that is much higher than previously estimated.
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1 - University of Utah, Biology, 257 South 1400 East, Salt Lake City, UT, 84112, USA
2 - University of Utah, Biology, 257 South 1400 East, Salt Lake City, UT, 84112, USA
xylem structure and function
single vessel method
Presentation Type: Oral Paper:Papers for Topics
Location: Cottonwood A/Snowbird Center
Date: Monday, July 27th, 2009
Time: 8:15 AM