Conifer epicuticular wax as a biomarker of air pollution: an overview

Epicuticular wax covering the conifer tree species surface has been used, mainly in conifers, as a biomarker of air pollution damage. Using Scanning Electron Microscopy (SEM) various alterations in wax structure and chemistry caused by natural and anthropogenic factors have been noticed. SEM enables to evaluate wax deterioration at a very early stage, before visible symptoms occur. Symptoms of wax injury are, in general, not specific to the air pollutant type. Most common alterations in wax were the following: an undeveloped structure, various type of wax tubes fusion or erosion (deformed and disfunctioned stomatal complexes, a decrease in wax tube distribution, increased enrichment of completely amorphous stage), shifted annual wax erosion rate, chemical and needle wettability changes. To use SEM as an accurate tool for evaluating wax alteration, it is essential to distinguish air pollution and natural factors from artefacts caused by inappropriate usage of technique.