EFFECTS OF OZONE ON LEAF SENESCENCE IN SPRING WHEAT - POSSIBLE CONSEQUENCES FOR GRAIN-YIELD

Results from three open-top chamber experiments, in which field grown spring wheat was exposed to different concentrations of ozone, were us ed in order to study the negative effect by ozone on leaf duration. In 1987 a clear pattern of fast yellowing with increasing ozone concentr ation was observed. In 1988, the flag leaf development was characteris ed by studying the ultrastructure of cells and the senescence was quan tified by the average chloroplast area. A consistent pattern of enhanc ed senescence, expressed as a decrease in the chloroplast area, togeth er with an increased ozone concentration was observed, as well as a li near relationship between grain yield and flag leaf duration. In 1995, an experiment was performed in which ozone fumigation of the plants l ook place either before or during and after anthesis. Ozone gave rise to a decrease in the green leaf area of plants only with exposure duri ng and after anthesis. It is concluded that a limited shortening of le af duration is likely to affect only the accumulation of total biomass (accelerated senescence), while higher rates of senescence stop the w hole life cycle of the plant prematurely, thus influencing also the ca rbon allocation in plants (premature senescence).