Toxic effects of exhaust emissions on spruce Picea abies and their reduction by the catalytic converter

Exhaust emissions from automobiles have been frequently connected with a new type of forest disease which is described for conifers and, more recently, also for deciduous trees. The use of the catalytic converter for pollution control and, consequently, as a remedy for forest decline, has been extensively advocated. No data are yet available on the efficiency of catalytic devices with respect to the toxicity of exhaust emissions. We have therefore studied this question in Norway spruce Picea abies (L.) Karst. under defined conditions. The efficiency of the catalyst was tested with concentrations of exhaust emissions which produced significant injuries within a limited period of time. A fast reduction of photosynthetic capacity and impairment of stomatal regulation was observed after a fumigation of only 15 min without a catalytic converter, followed by changes in colour and, finally, by needle dropping. During the early stages, buds were not injured and developed into healthy shoots. Consequently, symptoms of an inner browning and needle dropping could be mimicked. In the presence of a catalytic converter, essentially no damage to spruce could be observed under analogous conditions.