Ozone accelerates structural degradation of epicuticular wax on Norway spruce needles

Abstract

Scanning electron microscopy was used to investigate the effects of O., fumigation (70 d of 240 μg O3m−3 for 6 h d−1 during a 12 h photoperiod) on the condition of the epicuticular wax that fills and surrounds the stomatal antechamber of the needles of seven clones of Norway spruce (Picea abies (L.) Karst.). The rate of change of the physical structure of the wax differed between clones, but in all eases O., accelerated the process on current and previous year's needles. The change consisted of a transition from a crystalline array of fine tubes to an amorphous, ‘melted’ layer with no visible structure. This resulted in a higher frequency of stomata occluded by an apparently continuous plug. In four clones, O3, fumigation resulted in 70–80 %, of the stomata on previous year's needles being occluded, in contrast to 7–28 % in charcoal‐filtered air. Five of the clones showed a greater effect of O3, on the wax of the previous year's needles than on current needles. The physiological consequences of such O.,‐induced effects are discussed. Premature wax degradation induced by O3, and/or acid mist may have contributed to the decline of spruce in high‐altitude forests of continental Europe. Copyright © 1988, Wiley Blackwell. All rights reserved