Effect of simulated acid rain on the epicuticular wax of Scots pine needles under northerly conditions

In the extreme N of Finland during 1985-1988, pH 3 treated Pinus sylvestris had received a sulphur load of 7.48 g m^-2 and a nitrogen load of 2.62 g m^-2, and pH 4 treated pines a S load of 1.23 g m^-2 and a N load of 0.43 g m^-2 in addition to ambient deposition. No visible symptoms of acid rain injury were observed in the needles, but their growth was significantly reduced. Delayed development of the epistomatal waxes and 4 types of deformed stomatal complex were found by scanning electron microscopy. The rapid erosion of young, undeveloped waxes increased needle wettability (11%) significantly, but the quantity of chloroform-soluble waxes had decreased only slightly. The effects of acid rain on the epicuticular waxes were accentuated during unfavourable growing seasons with reduced effective temperature sums. -from Authors