LEAF SURFACE-PROPERTIES OF NORWAY SPRUCE NEEDLES EXPOSED TO SULFUR-DIOXIDE AND OZONE IN AN OPEN-AIR FUMIGATION SYSTEM AT LIPHOOK

Samples of current-year and 1-year-old foliage were taken from Norway spruce (Picea abies (L.) Karst.) trees in April 1991, 4 months after a 3-4 year controlled fumigation with O-3 and SO2 in the open at Liphoo k, south-east England. Trees were grown in seven plots, and treated in a factorial design with three levels of SO2 and two levels of O-3 (am bient and c. 1.3 x ambient), with an extra ambient air plot., All stat istical analyses were made on plot means. Leaf wettability, as measure d by the contact angle of water droplets, was significantly affected b y needle age and by SO2 treatment (P < 0.05) in older needles, decreas ing with increasing SO2 concentration. There was no effect of O-3 On w ettability, and no effect of any treatment on amounts of surface wax e xtracted by immersion of needles in chloroform. Electrolyte leakage ra tes from detached current-year needles were not affected by prior expo sure to O-3, but decreased significantly (P = 0.034) with increasing e xposure to SO2. There was no detectable effect of fumigation on the ra te of water loss from detached needles. Similarly, there was no effect of fumigation on the dry weight/fresh weight ratio of needles. The to tal sulphur content of needles increased significantly (P < 0.0001) wi th exposure to SO2 and with needle age. Amounts of water-extractable s ulphate, however, varied greatly among plots, but with no pattern with respect to fumigation treatment. It is concluded that leaf wettabilit y and electrolyte leakage rates may be good indicators of the persiste nt effects of SO2 on Norway spruce growing in the open air, and that t he observed changes in leaf surface properties in response to SO2 fumi gation have implications for the processes, both biotic and abiotic, t hat occur on leaf surfaces.