Effects of enhanced O3 and CO2 enrichment on plant characteristics in wheat and corn

The effects of CO2 enrichment and O3 induced stress on wheat (Triticum aestivum L.) and corn (Zea mays L.) were studied in field experiments using open-top chambers to simulate the atmospheric concentrations of these two gases that are predicted to occur during the coming century. The experiments were conducted at Beltsville, MD, during 1991 (wheat and corn) and 1992 (wheat). Crops were grown under charcoal filtered (CF) air or ambient air + 40 nl liter−1 O3 (7 h per day, 5 days per week) having ambient CO2 concentration (350 μl liter−1 CO2) or + 150 μl liter−1 CO2 (12 h per day.). Averaged over O3 treatments, the CO2-enriched environment had a positive effect on wheat grain yield (26% in 1991 and 15% in 1992) and dry biomass (15% in 1991 and 9% in 1992). Averaged over CO2 treatments, high O3 exposure had a negative impact on wheat grain yield (−15% in 1991 and −11% in 1992) and dry biomass (−11% in 1991 and −9% in 1992). Averaged over CO2 treatments, high O3 exposure decreased corn grain yield by 9%. No significant interactive effects were observed for either crop. The results indicated that CO2 enrichment had a beneficial effect in wheat (C3 crop) but not in corn (C4 crop). It is likely that the O3-induced stress will be diminished under increased atmospheric CO2 concentrations; however, maximal benefits in crop production in wheat in response to CO2 enrichment will not be materialized under concomitant increases in tropospheric O3 concentration.