EPICUTICULAR WAX OF SUB-ARCTIC SCOTS PINE NEEDLES - RESPONSE TO SULFUR AND HEAVY-METAL DEPOSITION

The response of epicuticular wax of Scots pine (Pinus sylvestris L.) n eedles to dry- and wet- deposited sulphur and heavy metals was investi gated at six sites located 10-110 km from the Monchegorsk Cu-Ni smelte r on the Kola Peninsula, North-West Russia, and in a long-term irrigat ion experiment where pines were exposed over four growing seasons (199 1-1994) to either acid rain treatment at pH 3.1 (H2SO4), metal treatme nt at pH 5.7 (Cu and Ni) or a combination of these at pH 3.1. Needle w ettability exhibited a closer relationship with epistomatal wax tube d istribution (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 determine d 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 n o gradient was observed in the proportion of secondary alcohols or hyd roxy 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 1 994 due to a 6.5-13.2 degree greater wettability of the 37-49-month-ol d acid-treated needles relative to the irrigated or dry controls. Sulp huric 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 na tural wax ageing, but at an accelerated rate. Changes in wax chemical composition might also be caused by pollutant-induced metabolic change s in elongating needles.