Effects of ozone and acidic fog on red spruce needle epicuticular wax ultrastructure

The effect of ozone and acidic fog on the epicuticular wax structure of elongating red spruce (Picearubens Sarg.) was examined. Needle exposure to 70 and 250 ppb ozone for 11 weeks resulted in a coalescence of crystalline tube ends within epistomatal chambers. Exposure to acid fog at pH 3.0 resulted in the formation of amorphous wax deposits over the existing tubes within the epistomatal chambers. New structures consisting of upright, irregular wax plates were observed in nonstomatal areas on needles exposed to pH 3.0 fog. These findings indicate that ozone and acid fog applied at near ambient doses can alter epicuticular wax ultrastructure on elongating red spruce needles. Ultrastructural changes induced by ozone and acid fog resulted from a direct pollutant interaction with wax crystallization and wax biosynthesis, respectively, and were not due to erosion or weathering of needle surfaces.