Effects of Ozone on Leaf Senescence in Spring Wheat - Possible Consequences for Grain Yield

Abstract

Results from three open-top chamber experiments, in which field grown spring wheat was exposed to different concentrations of ozone, were used in order to study the negative effect by ozone on leaf duration. In 1987 a clear pattern of fast yellowing with increasing ozone concentration was observed. In 1988, the flag leaf development was characterised by studying the ultrastructure of cells and the senescence was quantified by the average chloroplast area. A consistent pattern of enhanced senescence, expressed as a decrease in the chloroplast area, together with an increased ozone concentration was observed, as well as a linear relationship between grain yield and flag leaf duration. In 1995, an experiment was performed in which ozone fumigation of the plants took place either before or during and after anthesis. Ozone gave rise to a decrease in the green leaf area of plants only with exposure during and after anthesis. It is concluded that a limited shortening of leaf duration is likely to affect only the accumulation of total biomass (accelerated senescence), while higher rates of senescence stop the whole life cycle of the plant prematurely, thus influencing also the carbon allocation in plants (premature senescence).