Growth and yield responses of winter wheat to mixtures of ozone and carbondioxide

Ozone (O-3) in the troposphere can cause plant stress, whereas elevated CO2 generally enhances plant growth. Until recently, few studies have consider ed whether O-3 can affect plant response to CO2 or vice versa. We examined these possibilities for soft red winter wheat (Triticum aestivum L.). Plant s were grown in 14-L pots and exposed in open-top field chambers to all com binations of three CO, and three O-3 treatments. The CO2 treatments were am bient (approximately 380 muL L-1), or ambient with CO2 added for 24 h d(-1) to achieve mean concentrations of approximately 540, or 700 muL L-1. The O -3 treatments were charcoal-filtered air (CP), 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 r elatively sensitive; these cultivars were; tested in Exp. 2. Foliar injury caused by O-3 was suppressed by elevated CO2 in both experiments. In Exp. 1 , plant size and yield increased with CO, enrichment in the NF and NF+ trea tments, but not in the CF treatment. However, the O-3 x CO2 interaction was rarely significant. In Exp. 2, growth and yield of C9904 was suppressed mo re by O-3 than was that of C9835. Because of cultivar differences in sensit ivity to O-3, CO2 enrichment caused greater amelioration of O-3 stress and greater enhancement for C9904 than for C9835. Significant cultivar x O-3 x CO2 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 CO2 when investigating effec ts of O-3 or CO2 on plant systems.