Effects of ozone and acidic fog on red spruce needle epicuticular wax production, chemical composition, cuticular membrane ultrastructure and needle wettability.

Abstract

One-year-old red spruce (Picea rubens Sarg.) seedlings were exposed, from bud break, to ozone (O3 ) and acidic fog for 14, 42 or 77 days. Ozone was more damaging than acidic fog to epicuticular wax. Wax quantity on needles exposed to charcoal-filtered air (CFA) and pH 4.2 fog (control) increased from 14 to 42 days, but decreased by 77 days. Exposure of elongating needles to 70 ppb O3 and pH 4.2 fog reduced the rate of de novo wax synthesis. Red spruce wax is composed of secondary alcohols (50%), nonacosane diols (25%), alkyl esters (12%), primary alcohols (6 %), estolides (2 %), fatty acids (3 %), and hydroxy-fatty acids (2 %). Wax chemical composition varied temporally. Needles exposed to O3 had significantly less secondary alcohols, diols, alkyl esters, fatty acids, and hydroxy-fatty acids than needles exposed to CFA. Production of secondary alcohols was significantly reduced following needle exposure to fog at pH 3.0. Cuticular membrane thickness increased significantly following needle exposure to O3 . The increase in thickness at 250 ppb O3 was due to a new amorphous layer which appeared above the reticulate layer. Contact angles on needles exposed to CFA and pH 4.2 fog increased from 92° after 14 days to 96° after 42 days, then declined to 77° after 77 days. Needle exposure to O3 for 42 or 77 days significantly decreased contact angles.