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 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 k(s) 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), k(s) 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 k(s). 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 k(s) measured under steady and non-steady pressure gradients. With the exception of western red cedar, a conifer with simple pit membranes, the differences in k(s) 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 KCl than with H2O. In white oak, there were no differences in k(s) 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 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.
Full-textDOI: · Available from: Jean-Christophe Domec, May 29, 2015
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ABSTRACT: Sap water is distributed and utilized through xylem conduits, which are vascular networks of inert pipes important for plant survival. Interestingly, plants can actively regulate water transport using ion-mediated responses and adapt to environmental changes. However, ionic effects on active water transport in vascular plants remain unclear. In this report, the interactive ionic effects on sap transport were systematically investigated for the first time by visualizing the uptake process of ionic solutions of different ion compositions (K+/Ca2+) using synchrotron X-ray and neutron imaging techniques. Ionic solutions with lower K+/Ca2+ ratios induced an increased sap flow rate in stems of Olea europaea L. and Laurus nobilis L. The different ascent rates of ionic solutions depending on K+/Ca2+ ratios at a fixed total concentration increases our understanding of ion-responsiveness in plants from a physicochemical standpoint. Based on these results, effective structural changes in the pit membrane were observed using varying ionic ratios of K+/Ca2+. The formation of electrostatically induced hydrodynamic layers and the ion-responsiveness of hydrogel structures based on Hofmeister series increase our understanding of the mechanism of ion-mediated sap flow control in plants.PLoS ONE 05/2014; 9(5):e98484. DOI:10.1371/journal.pone.0098484 · 3.53 Impact Factor
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ABSTRACT: Xylem vulnerability to cavitation and response of water potential (Ψ), stomatal conductance (g s), and net photosynthesis (P n) to drought are potentially important mechanisms of drought resistance. We compared Ψ, g s, P n, and cavitation vulnerability of shoot and root xylem among co-occurring ponderosa pine (Pinus ponderosa var. scopulorum Dougl. Ex Laws.), pinyon pine (Pinus edulis Engelm.), and Utah juniper (Juniperus osteosperma [Torr.] Little) at a forest-woodland ecotonal site in northern Arizona to elucidate drought resistance mechanisms of these species. Juniper shoots partly regulated Ψ during drought via stomatal closure, but regulation was weaker than that for ponderosa and pinyon pines, which had similar water relations and P n responses to drought. Midday g s and P n during summer drought were positive for juniper (g s = 14.3 mmol m−2 s−1, P n = 1.23 μmol m−2 s−1) but near zero for ponderosa (g s = 0.7 mmol m−2 s−1, P n = −0.02 μmol m−2 s−1) and pinyon (g s = 1.5 mmol m−2 s−1, P n = −0.18 μmol m−2 s−1) pines. Cavitation vulnerability of shoots and roots was lower for juniper than for both pines. The water potential inducing 50% loss in xylem hydraulic conductivity (Ψ50) for juniper was 5.0 MPa more negative for shoots and 3.9 MPa more negative for roots compared with the respective tissues of the pine species. Pinyon pine (Ψ50 = −2.71 MPa) was slightly more vulnerable to cavitation than ponderosa pine (Ψ50 = −3.42 MPa) for shoots, whereas root vulnerability was similar for both pines (Ψ50 = −1.69 MPa for pinyon; −1.98 MPa for ponderosa). Roots of all species were more vulnerable to cavitation than shoots. Our results show an important role of cavitation vulnerability in the greater drought resistance of Utah juniper than pinyon and ponderosa pines but not for the presumed greater drought resistance of pinyon pine than ponderosa pine.Forest Science 10/2013; 59(5):524-535. DOI:10.5849/forsci.12-053 · 1.52 Impact Factor
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ABSTRACT: The xylem hydraulic efficiency and safety is usually measured on mechanically unstressed samples, although trees may be exposed to combined hydraulic and mechanical stress in the field. We analysed changes in hydraulic conductivity and vulnerability to drought induced embolism during static bending of Picea abies and Pinus sylvestris branches as well as the effect of dynamic bending on the vulnerability. We hypothesised this mechanical stress to substantially impair xylem hydraulics. Intense static bending caused an only small decrease in hydraulic conductance (-19.5 ±2.4% in P. abies) but no shift in vulnerability thresholds. Dynamic bending caused a 0.4 and 0.8 MPa decrease of the water potential at 50 and 88% loss of conductivity in P. sylvestris, but did not affect vulnerability thresholds in P. abies. With respect to applied extreme bending radii, effects on plant hydraulics were surprisingly small and are thus probably of minor eco-physiological importance. More important, results indicate that available xylem hydraulic analyses (of conifers) sufficiently reflect plant hydraulics under field conditions.Plant Cell and Environment 02/2014; 37(9). DOI:10.1111/pce.12307 · 5.91 Impact Factor