Characterization of yield, antioxidant and stomatal response in wheat grown in open-top chambers under variations in atmospheric ozone, carbon dioxide, and soil moisture

Two winter-wheat (Triticum aestivum) cultivars, Gore and Susquehanna, were grown in open-top chambers (OTC). Plants were grown under two moisture regimes (well-watered and restricted moisture) at two levels of ozone (charcoal-filtered air and non-filtered air supplemented with 30 ppb O3). The charcoal-filtered and high ozone treatments were performed at two carbon dioxide levels: ambient and ambient supplemented with 150 ppm CO2. Both cultivars were also grown under well-watered conditions, in OTC with non-filtered air, as well as in ambient conditions (no OTC) in order to assess possible chamber effects. Flag leaf samples were collected and analyzed for antioxidants and antioxidant enzyme activity. Leaf stomatal conductance and grain yield were also measured and compared with plant antioxidant responses. The results of this study provide insight into factors that contribute to the plant's response to ozone under environmentally relevant exposure concentrations. Cultivar Gore exhibited greater antioxidant enzyme activity and lower total ascorbate content than cultivar Susquehanna. Both cultivars showed yield reductions in response to ozone, with Gore tending to show a greater response. Under elevated ozone, both cultivars showed similar stomatal conductance and an increase in total glutathione content. Cultivar Susquehanna also exhibited a greater response in ascorbate peroxidase activity. Elevated carbon dioxide resulted in stomatal closure and, under low ozone, induced antioxidant changes that could enhance defensive capacity for oxidative stress. Yield under the combination of elevated ozone and carbon dioxide tended to be greater than for elevated ozone alone.{09}The results suggest that plant response to ozone depends upon a number of factors working together. Reduced stomatal conductance may be important as a first step that limits ozone uptake. Once ozone has entered the plant, the comparison of results for the more tolerant cultivar Susquehanna with the less tolerant cultivar Gore, suggests that the ability to respond to oxidative stress by increasing enzyme activity is also important. The availability of high pools of antioxidants may further contribute to enhanced oxidative defense capabilities. Future studies of the antioxidant defense system as a whole, rather than an individual enzyme or antioxidant level, may provide an improved understanding of plant response to ozone.