Problems in Interpreting Effects of Air Pollutants on Spruce Epicuticular Waxes

Abstract

Spruce needles are covered with rod-like crystals, which also fill the antechambers of the stomata with a dense meshwork. The scanning electron microscope (SEM) is a very useful for studying epicuticular wax structures; with no intricate or laborious preparation, it is possible to obtain valuable information about the needle surface. Because the epicuticular wax layer forms a barrier between the plant and its environment, all influences that reach the surface from outside impact on this layer and, therefore, changes in epicuticular wax structure serve as diagnostic criteria for damage caused by air pollutants. This pollution influence begins as fusion of wax rods at the tips and results finally in total loss of the crystalline structure.

Despite the simplicity of SEM investigations, alterations (artefacts) can occur to wax structures that may be confused with alterations caused by air pollutants (i. e., a too dense layer of twigs and needles, or careless handling with tweezers, results in mechanical damage that often influences the entire surface). Overheating occurring during transport or preparation and/or incorrect storage also produce artefacts.

If the occurrence of such artefacts is taken into consideration, several contradictory interpretations of effects of air pollutants on epicuticular waxes can be explained.