Dynamic variation in sapwood specific conductivity in six woody species

Department of Wood Science and Engineering, Oregon State University, Corvallis, OR 97331, USA.
Tree Physiology (Impact Factor: 3.66). 11/2007; 27(10):1389-400. DOI: 10.1093/treephys/27.10.1389
Source: PubMed


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.

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Available from: Jean-Christophe Domec, Oct 07, 2015
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    • "In the case of conifers , pit deformation may cause complete displacement of the torus, seal capillary seeding or torus capillary seeding by enlargement of pores within the torus (Tyree et al. 1994; Hacke & Sperry 2001; Domec et al. 2006; Cochard et al. 2009; Hacke & Jansen 2009; Delzon et al. 2010; Jansen et al. 2012). In addition, stretching of cell walls may enlarge cell wall pores and cause additional locations for air seeding (Domec et al. 2007). (4) Bending of branches may also cause local changes in tension, as water columns are compressed and stretched, especially under dynamic bending conditions. "
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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 · 6.96 Impact Factor
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    • "vary in response to changes in fluid ionic strength (I c ; van Ieperen et al., 2000; Zwieniecki et al., 2001; López- Portillo et al., 2005; Pittermann et al., 2005; Wheeler et al., 2005; Choat et al., 2006; Hacke et al., 2006; Domec et al., 2007; Nardini et al., 2007; Aasamaa and Sõber, 2010), composition with respect to specific cations (van Ieperen et al., 2000; Zwieniecki et al., 2001; Gascó et al., 2006), pH (Zwieniecki et al., 2001), and concentration of proteins and polysaccharides (Neumann et al., 2010). "
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    ABSTRACT: In perfusion experiments, the hydraulic conductance of stem segments (Kxylem) responds to changes in the properties of the perfusate such as the ionic strength (Ic), pH and cationic identity. We review the experimental and theoretical work on this phenomenon. We then proceed to explore the hypothesis that electrokinetic effects in the bordered pit membrane (BPM) contribute to this response. In particular, we develop a model based on electroviscosity in which hydraulic conductance of an electrically charged porous membrane varies with the properties of the electrolyte. We use standard electrokinetic theory, coupled with measurements of electrokinetic properties of plant materials from the literature to determine how the conductance of BPMs, and therefore Kxylem, may change due to electroviscosity. We predict a non-monotonic variation of Kxylem with Ic with a maximum reduction of 18%. We explore how this reduction depends on the characteristics of the sap, and features of the BPM-pore size, density of chargeable sites, and their pKa. Our predictions are consistent with changes in Kxylem observed for physiological values of sap Ic and pH. We conclude that electroviscosity is likely responsible, at least partially, for the electrolyte-dependence of conductance through pits, and that electroviscosity may be strong enough to play an important role in other transport processes in xylem. We conclude by proposing experiments to differentiate the impact of electroviscosity on Kxylem from that of other proposed mechanisms.
    Plant physiology 09/2013; 163(2). DOI:10.1104/pp.113.219774 · 6.84 Impact Factor
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    • "Closed symbols indicates significant differences (P < 0.05) and open symbols indicates non significant differences. cause other problems that alter K (Sperry and Tyree 1990, Domec et al. 2007). If K is to be measured in the presence of embolism, increasing P/L to minimize K 1pt error is not an option because of the possibility for embolism reversal. "
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    ABSTRACT: Xylem hydraulic conductivity (K) is typically defined as K = F/(P/L), where F is the flow rate through a xylem segment associated with an applied pressure gradient (P/L) along the segment. This definition assumes a linear flow-pressure relationship with a flow intercept (F(0) ) of zero. While linearity is typically the case, there is often a non-zero F(0) that persists in the absence of leaks or evaporation and is caused by passive uptake of water by the sample. In this study, we determined the consequences of failing to account for non-zero F(0) for both K measurements and the use of K to estimate the vulnerability to xylem cavitation. We generated vulnerability curves for olive root samples (Olea europaea) by the centrifuge technique, measuring a maximally accurate reference K(ref) as the slope of a four-point F vs P/L relationship. The K(ref) was compared with three more rapid ways of estimating K. When F(0) was assumed to be zero, K was significantly under-estimated (average of -81.4 ± 4.7%), especially when K(ref) was low. Vulnerability curves derived from these under-estimated K values overestimated the vulnerability to cavitation. When non-zero F(0) was taken into account, whether it was measured or estimated, more accurate K values (relative to K(ref) ) were obtained, and vulnerability curves indicated greater resistance to cavitation. We recommend accounting for non-zero F(0) for obtaining accurate estimates of K and cavitation resistance in hydraulic studies.
    Physiologia Plantarum 03/2012; 146(2):129-35. DOI:10.1111/j.1399-3054.2012.01619.x · 3.14 Impact Factor
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