IMPACT OF OZONE ON GROWTH AND YIELD PARAMETERS OF 2 SPRING WHEAT CULTIVARS (TRITICUM-AESTIVUM L)

In 2 consecutive years, potted plants of two spring wheat cultivars (Triticum aestivum L.), 'Star' and 'Turbo' were grown in open-top chambers and exposed to three (1988) or five (1988) levels of ozone (O3) applied for 8-h daily (8.00-16.00 h) over the whole growing season. Exposure variants consisted of charcoal-filtered air (CF; control) and CF supplemented with O3 resulting in mean treatment concentrations (mu-g.m-3) of 8, 50 and 101 (1988) and 20, 60, 121, 184 and 221 (1989) on an 8-h basis, and 5, 18 and 34 (1988) and 10, 25, 45, 67 and 78 (1989) on a 24-h basis, to which all results were related. During the two experimental periods, the corresponding O3 concentrations in ambient air were 55 and 75-mu-g.m-3 (24-h mean). Assessments of effects were carried out by measuring total aboveground biomass and various yield parameters. In comparison to charcoal-filtered air, O3 levels of 34 and 45-mu-g.m-3 significantly reduced growth and yield, respectively, of both cultivars in both years. At the lower treatment levels (18 and 25-mu-g.m-3), controversial results between the growing seasons and between the cultivars were obtained, e.g., as either no effects or slight stimulations of growth and yield were observed. While in 1988 'Star' was more affected by the pollutant than 'Turbo', similar O3 concentrations in 1989 produced an opposite result. In 1989, 'Turbo' was more susceptible than 'Star' to the higher O3 treatments. Low O3 concentrations seemed to affect total aboveground biomass more than grain yield, a reaction which changed with higher treatment levels. Visible symptoms, which could clearly be related to O3, were only observed at O3 levels equal or higher than 34-45-mu-g.m-3. The results, which demonstrate that current O3 levels in ambient air are potentially phytotoxic to wheat, are discussed in close relation to other recent studies in Europe on O3 effects on growth and yield of wheat.