© 2007 Heron Publishing—Victoria, Canada
Dynamic variation in sapwood specific conductivity in six woody species
Jean-Christophe Domec (1, 2), Frederick C. Meinzer (3), Barbara Lachenbruch (1) and Johann Housset (4)
1. Department of Wood Science and Engineering, Oregon State University, Corvallis, OR 97331, USA / 2. Corresponding author (jc.domec@oregonstate.edu) / 3. USDA Forest Service, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331, USA / 4. Institut National Agronomique Paris-Grignon, 17 rue Claude Bernard, Paris 75005, France / Received December 11, 2006; accepted January 19, 2007; published online July 3, 2007
Summary
Our goals were to quantify how non-embolism-inducing pressure gradients influence trunk sapwood specific conductivity (ks) and to compare the impacts of constant and varying pressure gradients on ks with KCl and H2O as the perfusion solutions. We studied six woody species (three conifers and three angiosperms) which varied in pit membrane
structure, pit size and frequency of axial water transport across pits (long versus short conduits). Both stepwise (“steady”)
and nonlinear continuous (“non-steady”) decreases in the pressure gradient led to decreased ks in all species but white oak (Quercus garryana Dougl. ex Hook), a ring-porous and long-vesseled angiosperm. In one diffuse-porous angiosperm (red alder, Alnus rubra Bong.) and two conifers (western red cedar, Thuja plicata Donn. ex D. Don, and Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco), ks was 10–30% higher under steady pressure gradients than under non-steady pressure gradients, and a decrease in the pressure
gradient from 0.15 to 0.01 MPa m–1 caused a 20–42% decrease in ks. In another diffuse-porous angiosperm (maple, Acer macrophyllum Pursh) and in a third coniferous species (western hemlock, Tsuga heterophylla (Raf.) Sarg), there was no difference between ks measured under steady and non-steady pressure gradients. With the exception of western red cedar, a conifer with simple pit
membranes, the differences in ks between low and high pressure gradients tended to be lower in the conifers than in the diffuse-porous angiosperms. In Douglas-fir,
western red cedar and the diffuse-porous angiosperms, ks was higher when measured with KCl than with H2O. In white oak, there were no differences in ks whether measured under steady or non-steady pressure gradients, or when xylem was perfused with KCl or H2O. The species differences in the behavior of ks suggest that elasticity of the pit membrane was the main factor causing ks to be disproportionate to the pressure gradient and to the different pressure regimes. The results imply that, if nonlinearities
in pressure–flux relationships are ignored when modeling tree water relations in vivo, large errors will result in the predictions
of tree water status and its impact on stomatal control of transpiration and photosynthesis.
Keywords:
Darcy’s law, hydraulic architecture, non-steady, steady, tracheids, vessels, xylem.
