Responses of antioxidative enzymes to elevated CO2 in leaves of beech (Fagus sylvatica L.) seedlings grown under a range of nutrient regimes

To study whether responses of antioxidative enzymes to enhanced atmospheric CO2 concentrations are affected by plant nutrition, the activities of superoxide dismutase, catalase and peroxidase were investigated in leaves of 3-year-old beech trees grown with low (0.1 x optimum), intermediate (0.5 x optimum) and high (2 x optimum) nutrient supply rates in open-top chambers at either ambient (approximate to 355 mu mol mol(-1)) or elevated (700 mu mol mol(-1)) CO2 concentrations, These treatments resulted in foliar C/N ratios of about 20 in the presence of high and > 30 in the presence of low nutrient supply rates, Pigment and malondialdehyde contents were determined to assess plant stress levels, Low nutrient supply rates caused pigment loss, whereas elevated CO2 had no effect on pigmentation, Guaiacol peroxidase activities did not respond to either CO2 or nutrient treatment, Catalase activity decreased with decreasing nutrient supply rate and also in response to elevated CO2. Superoxidase dismutase activity was affected by both nutrient supply and CO2 concentration, In leaves from trees grown with the high-nutrient treatment, superoxide dismutase activity was low irrespective of CO2 concentration, In chlorotic leaves, superoxide dismutase activity was increased, suggesting an enhanced need for detoxification of reactive oxygen species, Leaves from plants grown under elevated CO2 with medium nutrient supply rates showed decreased malondialdehyde contents and superoxide dismutase activities, This suggests that the intrinsic oxidative stress of leaves was decreased under these conditions, These results imply that intrinsic oxidative stress is modulated;by the balance between N and C assimilation.