The influence of ozone and acid mist on the amount and wettability of the surface waxes in Norway spruce [Picea abies (L.) Karst.].

Three-year old Norway spruce [Picea abies (L.) Karst.] trees from two clones (4076 and 4102) of a medium altitude southern German provenance were transplanted in May 1986 into an acid brown earth soil. During the summers of 1987 and 1988 the trees were exposed in large-scale fumigation chambers (solardomes) to ozone at 100 or 20 nl 1-1 (control). Acid (pH 3.6) or control mist (pH 5.5) was applied daily to trees. The wettability of current and 1-year-old needles was assessed in November 1988 by measuring the contact angle of water droplets placed on needles, and the amount of surface wax was determined. The contact angle of water droplets on current and 1-year-old needles was significantly reduced by 100 nl 1-1 PPB ozone and/or acid mist, indicating that the wettability had increased, but the combined effect of ozone and acid mist was no more than additive. Exposure to the pollutants resulted in a slight decrease in the quantity of surface wax, but the effect was not significant. Ozone and acid mist treatment also increased the projected area of needles relative to their dry weight. The possible involvement of such effects in forest decline are discussed.