Imbricacy and Stomatal Wax Plugs Reduce Maximum Leaf Conductance in Southern Hemisphere Conifers

Abstract

An examination of the relationship between theoretical maximum leaf conductance as calculated from stomatal dimensions, and measured maximum leaf conductance was undertaken in a group of Southern Hemisphere conifers. The relative effects of stomatal wax plugs, found in most species of conifers in the Southern Hemisphere, and imbricate leaf arrangement were expressed as a percentage inhibition of maximum leaf conductance (gmax) calculated from the ratio of measured gmax to theoretical gmax. Because of the similar stomatal dimensions of all species, measured gmax was proportional to stomatal density in plugged and unplugged species, with species without wax plugs producing maximum leaf conductances on average 91% of calculated gmax, while in species with plugged stomata measured gmax was on average only 35% of theoretical gmax. There was no effect produced by imbricacy in itself, but when combined with epistomy, gmax was significantly reduced to about 17% of theoretical gmax. This is clearly illustrated by comparisons of juvenile–adult foliage, and closely related imbricate and nonimbricate species. The adaptational advantages of imbricacy and wax plugs, and the potential for inferring gmax of fossil taxa are discussed.