Interactive Effects of Elevated CO 2, 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

Abstract

Summary The aim of the present study was to address the complex interactions of environmental constraints, ozone and drought stress, with elevated atmospheric CO 2 on the activities of antioxidative enzymes and soluble protein contents in needles of Norway spruce trees ( Picea abies L.). Five-year-old spruce trees were kept from bud break in June until January of the following year in phytochambers under climatic conditions similar to those of a natural site in the Bavarian forest. The trees were well-supplied with nitrogen and exposed to either elevated CO 2 (ambient + 200 μLL -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 CO 2 levels. In each chamber, a subset of trees was subjected to episodical drought stress in summer. Needles from controls investigated in October (summer conditions) and January (winter conditions) showed little seasonal variation of superoxide dismutase (SOD), an approximately 2-fold reduction in catalase (CAT), and a 2-fold increase in guaiacol peroxidase (POD) activity. Exposure to elevated CO 2 did not affect the activities of any of these enzymes in October and January, respectively, but caused a significant reduction in soluble protein. Ozone had no significant effect. Drought stress caused memory effects. In January, needles from trees drought-stressed in summer contained higher activities of defence enzymes and soluble protein contents than needles from well-watered trees. Three weeks after the end of a drought episode in summer, needles from spruce trees grown at elevated CO 2 contained increased CAT and POD activities as compared to needles from trees grown at ambient CO 2 . This response was increased, if elevated ozone was present as an additional stress factor. These observations suggest that Norway spruce trees grown under elevated atmospheric CO 2 concentrations might better be able to compensate environmental stresses than trees grown at ambient atmospheric CO 2 concentrations.