Terpene emission and ozone stress

Monoterpene concentrations have been measured in four open-top chambers with Norway spruce (Picea abies L. Karst). In half of the chambers used in this study the trees had been exposed to charcoal-filtered air during five summer periods, in the others they had been exposed to ambient air with additional ozone during the same periods. Measurements were performed during two periods, one in September–October during the fifth treatment, and the other in April–May, just before the harvest. Higher terpene concentrations were usually found in the chambers with filtered air, but this difference disappeared when the concentrations were adjusted according to differences in biomass. Consequently, these results do not indicate that ozone stress, at the levels tested, would lead to an increased release of terpenes. The estimate of the emission rate of α-pinene, obtained using the results from the spring measurements, are in good agreement with the findings in other, comparable investigations.