Seasonal changes in antioxidants in red spruce as affected by ozone

Two-year-old red spruce (Picea rubens Sarg.) seedlings were exposed to various levels of ozone, from 0.4 to 3 times ambient levels, in open-top chambers in Ithaca, NY, USA. Exposures, which varied with changes in day length, were from 30 May to 16 December 1987 and 1 June to 1 December, 1988. During the second exposure period, ascorbic acid, total and oxidized glutathione, α-tocopherol, and superoxide dismutase were measured in current and previous year's needles at monthly intervals from May to July, and at bi-weekly intervals from September to December. Orthogonalized polynomials were used to model the response through time of each variable measured. A one-way analysis of variance model was fitted to every regression coefficient in each polynomial model to test for ozone effects on seasonal patterns of antioxidant levels. Ozone influenced seasonal changes in total glutathione, the oxidized/total glutathione ratio, and α-tocopherol in previous years's needles and α-tocopherol and superoxide dismutase in current year's needles. Averaged over the whole growing season, the oxidized/total glutathione ratio and superoxide dismutase showed an ozone treatment effect in both age classes. Mean total glutathione content increased in previous year's needles, but was not influenced by ozone in current year's needles. Mean oxidized glutathione content was higher with ozone exposure in current year's needles, but not in previous year's needles. The role of antioxidants in cold hardiness and ozone detoxification is discussed.