INTERACTIVE EFFECTS OF ELEVATED CO2, OZONE AND DROUGHT STRESS ON THE ACTIVITIES OF ANTIOXIDATIVE ENZYMES IN NEEDLES OF NORWAY SPRUCE TREES (PICEA-ABIES, [L] KARSTEN) GROWN WITH LUXURIOUS N-SUPPLY

The aim of the present study was to address the complex interactions o f environmental constraints, ozone and drought stress, with elevated a tmospheric CO2 on the activities of antioxidative enzymes and soluble protein contents in needles of Norway spruce trees (Picea abies L.). F ive-year-old spruce trees were kept from bud break in June until Janua ry of the following year in phytochambers under climatic conditions si milar to those of a natural site in the Bavarian forest. The trees wer e well-supplied with nitrogen and exposed to either elevated CO2 (ambi ent + 200 mu LL(-1)), elevated ozone (80 nLL(-1), from June to October ) or to a combination of both factors. Controls were grown with 20 nLL (-1) O-3 and ambient CO2 levels. In each chamber, a subset of trees wa s subjected to episodical drought stress in summer. Needles from contr ols investigated in October (summer conditions) and January (winter co nditions) showed little seasonal variation of superoxide dismutase (SO D), an approximately 2-fold reduction in catalase (CAT), and a 2-fold increase in guaiacol peroxidase (POD) activity. Exposure to elevated C O2 did not affect the activities of any of these enzymes in October an d January, respectively, but caused a significant reduction in soluble protein. Ozone had no significant effect. Drought stress caused memor y effects. In January, needles from trees drought-stressed in summer c ontained higher activities of defence enzymes and soluble protein cont ents than needles from well-watered trees. Three weeks after the end o f a drought episode in summer, needles from spruce trees grown at elev ated CO2 contained increased CAT and POD activities as compared to nee dles from trees grown at ambient CO2. This response was increased, if elevated ozone was present as an additional stress factor. These obser vations suggest that Norway spruce trees grown under elevated atmosphe ric CO2 concentrations might better be able to compensate environmenta l stresses than trees grown at ambient atmospheric CO2 concentrations.