A time-concentration study on the effects of ozone on spring wheat (Triticum aestivum L) .1. Effects on yield

Spring-sown wheat (Triticum aestivum L., cv. 'Promessa') was grown in open-top chambers and ambient-air plots at a site in the southeast of Ireland, and exposed to different concentrations of ozone in a 3-year study carried out from 1991 to 1993. The treatments used in the study were charcoal-filtered air, non-filtered air and non-filtered air to which extra ozone was added. Additional ozone was added to the treatments either as short-term high-concentration exposures or as long-term low-concentration exposures, Air filtration had no significant effect on grain yield, indicating that ambient levels of ozone over the experimental period in the study area did not have the potential to decrease the yield of spring wheat crops. Additional ozone exposures with higher peak concentrations had the most detrimental effect on grain yield. Short-term fumigation with ambient ozone plus 50 parts per billion (p.p.b.) in 1991 resulted in a 53% reduction in grain yield. In 1992 a similar cumulative exposure but with ambient ozone plus 25 p.p.b. applied over a longer time interval increased grain yield by 17%. In 1993 these observations were confirmed when an ozone exposure with higher peak concentrations significantly reduced grain yield, while an identical exposure with lower peak concentrations had no effect. Changes in grain yield were primarily the result of changes in grain filling. They were accompanied by changes in protein percentage as well as in the percentage of small, improperly filled grains, The results suggest that increased emphasis should be given to peak concentrations in the assessment of ozone effects on vegetation.