Integrative Plant Physiology
Thorn, Alexandra , Orians, Colin M. .
Modeling Xylem Sectoriality and Hydraulic Conductance: Anatomical Bases and Ecological Significance.
Sectoriality, the degree to which resource movement in plants is restricted by vascular pathways, varies among species. High sectoriality constrains growth in heterogeneous environments, while hypothesized benefits include cavitation resistance and disease isolation. To clarify the relationship between xylem anatomy and sectoriality, we developed a model for xylem sectoriality based on the Ohm's law analogy for hydraulic resistance. We model the xylem as two high-conductance pathways (two sectors), interconnected by a number of low-conductance connections (sensu intervessel pits). We show that high sectoriality results from either low conductance between sectors or high conductance within a sector. We used published hydraulic data for oak, maple, and birch in our model to increase understanding of sectoriality in these species. Model output suggests that the high sectoriality seen for maple compared to birch was due primarily to higher axial conductance: the two species have similar intersector conductance. Oak has much weaker intersector connections, and its sectoriality is further increased by high axial conductance (a pattern that may carry over to other ring-porous species with wide, low-resistance vessels). Our results suggest several factors that may affect sectoriality within species. Wide vessels grown as a plastic response to high water supply should increase sectoriality, unless intervessel connections increase at a comparable rate. This plasticity may mean that sectoriality in trees varies from year to year with water availability. Finally, sectoriality may differ between structures in the same plant: axial conductance in some tree species have been reported to be lower in distal branches and especially at branch junctions compared to the main trunk.
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1 - Tufts University, Department of Biology, 163 Packard Avenue, Medford, MA, 02155, USA
2 - Tufts University, Department of Biology
Ohm's law analogy
xylem structure and function.
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM