Geometrical and physicochemical considerations of the pit membrane in relation to air seeding: the pit membrane as a capillary valve

A.G. MEYRA; V.A. KUZ; G.J. ZARRAGOICOECHEA

TREE PHYSIOLOGY

Heron Publishing

Lugar: Victoria, Canada; Año: 2006

0829-318X

In this paper a theoretical treatment of some factors influencing air seeding at the pit membranes in the xylem vessels is given. Pit membrane structure, viewed as a three-dimensional mesh of intercross fibrils, and vulnerability to water stress induced air seeding are examined at the light of Young-Laplace equation. Simple geometrical considerations of the porous membrane show that the air-vapor-liquid interface curvature radius is a function of the fiber-fiber distance, the fiber radius, the wetting angle and the 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 it is a function of the geometry of the pit membrane and of the 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 separation. 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 forbid 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.