Growth and Yield Responses of Winter Wheat to Mixtures of Ozone and Carbon Dioxide

Ozone (O 3 ) in the troposphere can cause plant stress, whereas elevated CO 2 generally enhances plant growth. Until recently, few studies have considered whether O 3 can affect plant response to CO 2 or vice versa. We examined these possibilities for soft red winter wheat ( Triticum aestivum L.). Plants were grown in 14‐L pots and exposed in open‐top field chambers to all combinations of three CO 2 and three O 3 treatments. The CO 2 treatments were ambient (approximately 380 μL L −1 ), or ambient with CO 2 added for 24 h d −1 to achieve mean concentrations of approximately 540, or 700 μL L −1 The O 3 treatments were charcoal‐filtered air (CF), nonfiltered air (NF), or NF with O 3 added for 12 h d −1 (NF+). Mean O 3 concentrations in the CF, NF, and NF+ treatments were approximately 27, 45, and 90 nL L −1 In the first experiment, eight cultivars with widely different genetic backgrounds were tested. `Coker 9835' was relatively resistant to O 3 and `Coker 9904' was relatively sensitive; these cultivars were tested in Exp. 2. Foliar injury caused by O 3 was suppressed by elevated CO 2 in both experiments. In Exp. 1, plant size and yield increased with CO 2 enrichment in the NF and NF+ treatments, but not in the CF treatment. However, the O 3 × CO 2 interaction was rarely significant. In Exp. 2, growth and yield of C9904 was suppressed more by O 3 than was that of C9835. Because of cultivar differences in sensitivity to O 3 , CO 2 enrichment caused greater amelioration of O 3 stress and greater enhancement for C9904 than for C9835. Significant cultivar × O 3 × CO 2 interactions occurred for all growth and yield measures. These results are similar to results with other crops, and further emphasize the need to consider possible interactions between O 3 and CO 2 when investigating effects of O 3 or CO 2 on plant systems.