Boundary layer properties of highly dissected leaves: an investigation using an electrochemical fluid tunnel

Abstract

A method for modelling heat and mass ttansfer by diffusion-controlled electrode reactions in a fluid tunnel is described. In this procedure, a nickelplated leaf functions as a test electrode, and the convective transfer of ions to the leaf cathode in an electrolyte-filled flow tunnel is measured as a function of flow rate. The method permits the simulation of water vapour and heat transfer, and in particular, the determination of boundary layer conductances, by analogy with observed ion transfer. The approach is applicable to tnany problems in modelling heat and mass transfer between leaves and their surroundings, and is especially useful in examining the properties of leaves in which surface characteristics or overall shape are complex. Using this method, the properties of the highly dissected leaves of Achilica lanulosa with regard to forced convection were investigated. The leaves showed high transfer conductances, indicating that the effective unit of heat transfer was probably the individual leaf subelements. Conductances tended to be greater and effective characteristic dimensions smaller for the larger, more open leaves of a lower altitude population in contrast with leaves from high altitude plants. While the results provide insight into the properties of these cotnplex leaf shapes, difficulties in interpreting the findings are discussed, and a number of exploratory approaches are suggested for data analysis and interpretation.

Leaf development and morphogenesis

“…Reduced gibberellin activity can promote drought tolerance in tomato (Nir et al, 2014). Interestingly, more pronounced effects were observed in simple leaves than in compound leaves in this case (Gurevitch and Schuepp, 1990). Salinity can also affect leaf development.…”

The evolution and functional significance of leaf shape in the angiosperms

“…Likewise, because leaf lobing reduces the distance across the lamina, the rate of heat transfer is predicted to be greater in a lobed leaf than an unlobed leaf with equivalent area (Parkhurst et al 1968;Vogel 1968;Lewis 1972;Givnish 1978;Gurevitch and Schuepp 1990a).…”

“…The rate of heat transfer from lobed metal plates or lobed leaves coated in metal is greater than from shallow-lobed or unlobed ones (Parkhurst et al 1968;Thom 1968;Vogel 1970;Gottschlich and Smith 1982;Gurevitch and Schuepp 1990b;Roth-Nebelsick 2001). Artificial or coated leaves have been used because they enable boundary layer resistance to be investigated in the absence of transpiration.…”

Tansley Review No. 59 Leaf boundary layers

“…In electrochemical simulations with metal-coated leaves of various populations of the highly dissected Achillea lanulosa by Gurevitch & Schuepp (1990), leaf structure, including microscopic surface hairs, was left largely intact. The leaves showed high transfer conductances, in agreement with predictions of boundary layer theory for cylinders in crossfiow, with characteristic dimensions comparable to the diameter of individual leaf subelements.…”

“…the side of a square with the same surface area as the leaf), with a shape factor which accounts for differences in leaf shape (Thorpe & Butler, 1977). All such definitions are physically inappropriate for highly dissected, threedimensional leaf structures; in such cases effective characteristic dimensions may best be derived from observation of transfer, based on estimated surface area (Gurevitch & Schuepp, 1990).…”