The response of epicuticular wax of Scots pine (Pinus
sylvestris L.) needles to dry- and wet- deposited sulphur and
heavy metals was investigated at six sites located 10–110 km
from the Monchegorsk Cu-Ni smelter on the Kola Peninsula, North-West
Russia, and in a long-term irrigation experiment where pines were
exposed over four growing seasons (1991–1994) to either acid
rain treatment at pH 3·1 (H2SO4), metal
treatment at pH 5·7 (Cu and Ni) or a combination of these at pH
3·1. Needle wettability exhibited a closer relationship with
epistomatal wax tube distribution (WTD) than with chemical composition
of epicuticular wax. Water droplet contact angles (DCA) decreased
towards the smelter, and significant differences due to site were
noted for 26-month-old and 38-month-old needles. Significant
differences due to site were determined for secondary alcohols,
dehydroabietic acid and hydroxy fatty acids, the proportions of which
ranged from 22·5 to 48·9%, 6·2 to 22·4% and
0·6 to 2·6% respectively, depending on site and needle
age class. The proportion of dehydroabietic acid increased towards the
smelter, but no gradient was observed in the proportion of secondary
alcohols or hydroxy fatty acids. No major effect of experimentally
applied pollutants on the chemical composition or structure of the
epicuticular wax was observed. The effect of treatment on DCA was
significant in 1993 and 1994 due to a 6·5–13·2
degree greater wettability of the 37–49-month-old acid-treated
needles relative to the irrigated or dry controls. Sulphuric acid at
pH 3·1 did not increase needle wettability when combined with
copper and nickel sulphate in similar concentrations. These data
indicate that S deposition, especially H2SO4,
plays a more important role in needle surface deterioration than Cu
and Ni. Pollutant-induced changes in epicuticular wax structure and
needle wettability mimic natural wax ageing, but at an accelerated
rate. Changes in wax chemical composition might also be caused by
pollutant-induced metabolic changes in elongating needles.