Elevated CO 2 provides protection from O 3 induced photosynthetic damage and chlorophyll loss in flag leaves of spring wheat ( Triticum aestivum L., cv. ‘Minaret’)

Abstract

Spring wheat ( Triticum aestivum L., cv. ‘Minaret’) was grown in open-top chambers and exposed to two CO 2 concentrations (ambient and 680 ppmv) and two O 3 concentrations (ambient and ambient +50 or +90 ppbv) either from anthesis onwards or for the entire growing season. The aim of the experiment was to test whether elevated CO 2 could provide ‘protection’ to the crop against the damaging effects of elevated O 3 on flag leaf chlorophyll content and photosynthetic activity. The decline in flag leaf chlorophyll content following anthesis was unaffected by elevated CO 2. However, the reduction in chlorophyll content brought about by elevated O 3 was less in elevated compared with ambient CO 2. The rate of flag leaf photosynthesis was increased in elevated CO 2 and decreased in elevated O 3. When elevated CO 2 and elevated O 3 were combined the decrease attributed to O 3 was smaller than in elevated O 3 at ambient CO 2. These results confirm that elevated CO 2 provides some protection to a wheat crop against the damaging effects of O 3 on photosynthetic activity and chlorophyll content. However, the degree of protection varies between growing seasons and also appears to be related to the timing of exposure to elevated O 3.