Developmental and Structural Section
Pratt, R. Brandon , Jacobsen, Anna L. , Ewers, Frank W. , Davis, Stephen D. .
Xylem hydraulic and biomechanical tradeoffs in branches and roots of nine Rhamnaceae shrub species.
BIOMECHANICAL and hydraulic tradeoffs were examined in branches and roots of nine chaparral shrub species representing three different life history types: post-fire non-sprouters (NS), facultative sprouters (FS), and obligate sprouters (OS). The general pattern for xylem cavitation resistance of stems and roots was NS>FS=OS. Among branches, increased xylem cavitation resistance (the water potential at 50% loss of hydraulic conductivity [Ψ50]) was correlated with increased xylem density, bulk stem resistance to mechanical breakage (modulus of rupture [MOR]), resistance of vessels to implosion (the paired vessel thickness to span ratio [t/b]2), and negatively correlated to xylem capacitance. Roots were more susceptible to cavitation than branches for all but two of the examined species. For roots, as in branches, increased xylem cavitation resistance was correlated with increased MOR and (t/b)2, but unlike branches root cavitation resistance was not correlated to xylem density. Moreover, cavitation resistance for roots was negatively correlated with hydraulic efficiency (hydraulic conductivity divided by active xylem area [Ks] and hydraulic vessel diameter), but not for branches. Roots had greater Ks and hydraulic vessel diameters than branches. Xylem capacitance was not measured for roots. Branches and roots more resistant to cavitation are also biomechanically stronger, likely reflecting a need to resist vessel implosion under negative pressures. In branches, this mechanically robust design is linked to reduced capacitance but not reduced hydraulic efficiency. In contrast, increased cavitation resistance in roots comes at the cost of decreased hydraulic efficiency. Similar tradeoffs in roots and branches may reflect their shared need to safely transport water under negative pressures, whereas different tradeoffs may arise in roots versus branches due to differences in anatomy, biomechanical stresses experienced, and radial transport.
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1 - California State University Bakersfield, Department of Biology, 9001 Stockdale Hwy., Bakersfield, California, 93311-1099, USA
2 - Michigan State University, Department of Plant Biology, 166 Plant Biology Building, East Lansing, Michigan, 48824-1312, USA
3 - Pepperdine University, Natural Sciences Division, 24255 Pacific Coast Highway, Malibu, California, 90263-4321, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 312/Bell Memorial Union
Date: Monday, July 31st, 2006
Time: 4:00 PM