Dynamic variation in sapwood specific conductivity in six woody species

Abstract

Our goals were to quantify how non-embolism inducing pressure gradients influence trunk sapwood specific conductivity (k_s) and to compare the impacts of constant and varying pressure gradients on k_s with KCl and H₂0 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 k_s in all species but white oak: (Quercus garryana Dougl. ex Hook), a ring-porous and longvesseled angiosperm. In one diffuse-porous angiosperm (red alder, Alnus rubra Bong.) and two conifers (western red cedar, Thuja plicaia 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 kg 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, k_s was higher when measured with KCI than with H₂0. In white oak, there were no differences in ks whether measured under steady or non-steady pressure gradients, or when xylem was perfused with KCI or H₂0. The species differences in the behavior of k_s suggest that elasticity of the pit membrane was the main factor causing k_s 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.

Citation

Domec, Jean-Christophe; Meinzer, Frederick C.; Lachenbruch, Barbara; Housset, Johann. 2008. Dynamic variation in sapwood specific conductivity in six woody species. Tree Physiology: vol 27 pgs. 1389-1400