Effects of Acid Mist on Needle Surface and Water Status of Picea abies

Abstract

In various experiments carried out under controlled conditions in the greenhouse, we have shown that acid mist (pH 2.7-3.0) application affected the cuticle of spruce trees and led to a decomposition and melting of epicuticular waxes. Trees with such an affected cuticle had the same transpiration rate as control trees if abundant soil water was available. When soil water was low, however, trees with an affected cuticle transpired significantly more water than control trees. This effect was particularly evident at noon, when control trees showed virtually no transpiration in contrast to affected trees.

In a further set of experiments, in the spring, we tested the effect of frozen soil on the water status of young spruce trees that had been exposed to acid mist the preceding autumn. These affected trees, during periods of sunshine, had significantly lower water potential than the control trees. This investigation demonstrates that acid mist affects the water status of spruce trees. Because acid mist is common in the area near Frankfurt, we argue that decline symptoms in this area, including cuticle damage, are caused mainly by acid mist.