Tropospheric Ozone: A Stress Factor for Norway Spruce in Sweden

Nutrient and chlorophyll content, ultrastructural changes, photosynthesis, stem growth and biomass were studied in Norway spruce, Picea abies, exposed to three different concentrations of ozone for five seasons (1985-89) in open-top chambers. The treatments were charcoal-filtered air (CF), non-filtered, ambient air (NF) and non-filtered air enriched with ozone (NF+). The results show that ozone can change the ultrastructure of needles, decrease the content of chlorophyll and decrease the rate of photosynthesis, and that the extent of these changes depends on the length of exposure and the age of the needles and shoots. No significant effects of ozone on above-ground biomass were observed. Based on the results on photosynthesis, an attempt was made to model the canopy photosynthesis of 8 and 89 yr old trees. The results indicate that the ambient ozone concentrations in Sweden can reduce the canopy photosynthesis, and that the effect is small in young trees and becomes greater in old trees, mainly because of the different proportions of needle age classes. This paper is a summary document of the results, some of which have already been published elsewhere.