© 2007 Heron Publishing—Victoria, Canada
Geometrical and physicochemical considerations of the pit membrane in relation to air seeding: the pit membrane as a capillary
valve
Ariel G. Meyra (1), Victor A. Kuz (1) and Guillermo J. Zarragoicoechea (1, 2, 3)
1. IFLYSIB (UNLP, CONICET, CICPBA) C.C.565, (B1900BTE) La Plata, Argentina / 2. Comisión de Investigaciones Científicas de la Provincia de Buenos Aires, Buenos Aires, Argentina / 3. Corresponding author (vasco@iflysib.unlp.edu.ar) / Received September 18, 2006; accepted February 6, 2007; published online July 3, 2007
Summary
A theoretical treatment of some of the factors influencing air seeding at the pit membranes of xylem vessels is given. Pit
membrane structure, viewed as a three-dimensional mesh of intercrossing fibrils, and vulnerability to water-stress-induced
air seeding are examined in the context of the Young-Laplace equation. Simple geometrical considerations of the porous membrane
show that the vapor–liquid interface curvature radius is a function of fiber–fiber distance, fiber radius, wetting angle and
position of the wetting line. Air seeding (maximum pressure) occurs at the minimum curvature radius, therefore air seeding
is not simply determined by the fiber–fiber distance but is a function of the geometry of the pit membrane and of physicochemical
quantities like surface tension and wetting angle. As a consequence of considering a wetting angle different from zero, the
minimum curvature radius becomes larger than half the fiber–fiber distance. The present model considers that, for a given
pressure difference at the pit membrane, all local interface curvatures are the same. In this sense, pit membranes work as
variable capillary valves that allow or prevent air seeding by adjusting local curvatures and interface positions relative
to the pore-forming fibers, following the pressure differences across the membranes. The theoretical prediction for the air
seeding threshold is consistent with recent experimental data for angiosperm trees.
Keywords:
air-seeding pressure, curvature radius, Laplace equation.
