Water transport in xylem conduits with ring thickenings

Abstract

Helical or annular wall thickenings are not only present in protoxylem, but may also he a feature of the tracheids or vessel elements of secondary wood. The frequency of their occurrence tends to be a function of climatic factors and conduit diameter. In order to obtain a functional explanation for these structures, the hydrodynamic behaviour of xylem conduits with various patterns of annular wall thickenings was investigated numerically using a commercial CFD (Computational Fluid Dynamics) package. The fluid flow phenomena are presented in detail. The calculations show that the developing pressure gradient of the structures with corrugated walls is in each case lower than that of a smooth pipe with a diameter corresponding to the distance between two opposite thickenings. Furthermore, complex flow patterns with circulation zones between the thickenings develop which are dependent on the geometry of the wall. It may be hypothesized that these circulation zones influence the lateral water flow. The results are discussed with regard to the relationships between the water conduction function of the xylem and ecological factors.

Chemical agents transported by xylem mass flow propagate variation potentials

“…The Reynolds number for xylem flow (Ellerby and Ennos, ) can be estimated from the equation for flow in a smooth pipewhere ρ is the fluid density, v the velocity, d the xylem diameter and μ the dynamic viscosity. Using ⍴ = 1000 kg m −3 , v = 1 mm s −1 , d = 50 μm and μ = 10 −3 Pa s −1 , the approximate Reynolds number of flow in the xylem is 5 × 10 −2 , consistent with previous reports (Rand, ; Roth, ; Ellerby and Ennos, ). For a Reynolds number this low, the effect of pipe roughness is negligible (Moody, ); however, varying xylem profiles can modify the behaviour.…”

The mechanism of propagation of variation potentials in wheat leaves

“…D tur may be thousands of times larger than D mol (Levich, 1962). Turbulent convection in the xylem may be because of the composite trajectory of the water flow, which is caused by the complicated geometry of xylem vessels (Roth, 1996) and by wound-induced hydraulic wave propagation. The theoretically estimated high velocity of chemical substance transmission was analyzed experimentally by means of a radiotracer method.…”

Shoot orientation affects vessel size, shoot hydraulic conductivity and shoot growth rate in Vitis vinifera L.

“…Bending, even when carried out carefully or achieved in stages, may hinder sap flow in lignified shoots and is used in grapevine management to facilitate shooting and development of buds proximal to the bending point (Tassie & Freeman 1992). On a theoretical basis, bending can reduce water flow because the laminar xylem flow encounters a higher resistance if vessels are squeezed (Roth 1996). However, little experimental evidence is available on the effects of bending on the hydraulic conductivity of young, non-lignified shoots.…”