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 Liphook, 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 (ambient and c. 1.3 x ambient), with an extra ambient air plot., All statistical analyses were made on plot means. Leaf wettability, as measured by the contact angle of water droplets, was significantly affected by needle age and by SO2 treatment (P < 0.05) in older needles, decreasing with increasing SO2 concentration. There was no effect of O-3 On wettability, and no effect of any treatment on amounts of surface wax extracted by immersion of needles in chloroform. Electrolyte leakage rates from detached current-year needles were not affected by prior exposure to O-3, but decreased significantly (P = 0.034) with increasing exposure to SO2. There was no detectable effect of fumigation on the rate of water loss from detached needles. Similarly, there was no effect of fumigation on the dry weight/fresh weight ratio of needles. The total sulphur content of needles increased significantly (P < 0.0001) with exposure to SO2 and with needle age. Amounts of water-extractable sulphate, however, varied greatly among plots, but with no pattern with respect to fumigation treatment. It is concluded that leaf wettability and electrolyte leakage rates may be good indicators of the persistent effects of SO2 on Norway spruce growing in the open air, and that the observed changes in leaf surface properties in response to SO2 fumigation have implications for the processes, both biotic and abiotic, that occur on leaf surfaces.