EXPOSURE OF MATURE NORWAY SPRUCE TO OZONE IN TWIG-CHAMBERS - EFFECTS ON GAS-EXCHANGE

Little is known about ozone (O-3) effects on adult trees in the field, where ecophysiological parameters control pollutant uptake. It was the goal of this study to examine how ambient and above ambient O-3 concentrations affect gas exchange of mature Norway spruce (Picea abies (L.) Karst.). Therefore, twigs were enclosed in chambers and exposed to different O-3 concentrations for one and two seasons over three years. During winter periods twigs were maintained under ambient conditions. Data from the shade crown of spruce trees at 1000 m a.s.l. are presented. After one and two fumigation periods no clear treatment effects on gas exchange were observed in twigs fumigated with O-3 concentrations ranging from zero up to ambient (A)+60 ppb. However, O-3 at 90 ppb reduced photosynthesis and conductance. CO2 response curves indicated that in A+90 twigs the efficiency of CO2 uptake was diminished. Observed losses in P-n of A+90 twigs were greater than reductions in conductance indicating that stomatal closure alone did not limit CO2 uptake. We conclude that ambient and slightly above ambient O-3 concentrations do not alter gas exchange of mature Norway spruce. Therefore, suppositions on O-3 damage on mature spruce trees should be critically questioned.