Sperry, John S. , Smith, Duncan D. , von Allmen, Erica , Enquist, Brian J. , Savage, Van M. , Patrick, Lisa .
Integrating vascular principles into a general model for the structure and function of plant networks.
General models of hydraulic architecture are useful for their potential to predict water use and metabolic rate as a function of plant size and functional type. A previous model represented shoot architecture by a self-similar branching pattern that is space-filling, area-preserving, and converges on elastic similarity at larger size. Here we retain this external branching framework, but plumb it with an improved representation of the internal xylem pipework that derives from two long-established empirical patterns. 1) The log-linear relationship between conduit frequency (number per wood area) and mean conduit diameter. We call this the "packing function" because it is consistent with conduits filling the fraction of wood space that is not devoted to storage or mechanical support. 2) The tapering of conduits axially within a growth ring, and hence also radially across growth rings from pith to cambium. Axial and radial taper can be represented by a single "taper function" that describes the relationship between mean conduit diameter per growth ring and growth ring radius. Hypothetically, the taper function derives from the packing function if conduit diameter is maximized and conduit number is minimized at each branching level. This pattern minimizes flow resistance because fewer, wider conduits have lower resistance than many narrow ones. Taper diminishes as conduit diameter approaches the maximum that is set by mechanic or hydraulic constraints. Species-specific packing and taper functions were found to be consistent with this hypothesis for diffuse-porous Acer grandidentatum (maple) and ring-porous Quercus gambelii (oak). The larger vessel sizes in oak were associated with fewer vessels per growth ring, implying a trade-off between efficiency vs. redundancy of multiple transport pathways. Both species conformed to model assumptions of area-preserving branching and elastic similarity. The revised model improved the prediction of hydraulic parameters across functional types of woody plants.
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1 - University of Utah, Biology, 257 South 1400 East, Salt Lake City, UT, 84112, USA
2 - University of Utah, Department of Biology, 257 South 1400 East, Salt Lake City, Utah, 84112, U.S.A.
3 - University of Arizona, Department of Ecology and Evolutionary Biology, Tucson, Arizona, 85721, U.S.A.
4 - University of California, Department of Biomathematics, Los Angeles, California, 90095, U.S.A.
Presentation Type: Poster:Posters for Topics
Location: Event Tent/Cliff Lodge
Date: Monday, July 27th, 2009
Time: 5:30 PM