Effects of Ozone on Leaf Senescence, Photochemical Efficiency and Grain Yield in Two Winter Wheat Cultivars

The adverse effects of tropospheric ozone (O-3) on crop photosynthesis, growth and yield have been documented in numerous studies over the last decades, but little information from field experimentation exists on how modern European winter wheat cultivars respond to O-3. Two winter wheat cultivars (Astron and Pegassos) differing in development characteristics were exposed to non-filtered ambient air or non-filtered air plus 30ppb and non-filtered air plus 60ppb O-3 (8hday(-1)) in open-top field chambers. At several dates during growth, green leaf area was determined by destructive harvests. Leaf gas exchange, pigment content and xanthophyll cycle activity, and photochemical efficiency by chlorophyll a fluorescence were measured. O-3 exposure induced accelerated senescence with no difference between cultivars. Photosynthesis declined especially in Pegassos; however, stomatal conductance was hardly affected by O-3. Pigment contents were reduced by O-3 exposure, and de-epoxidation index increased. Photochemical efficiency (F-v/F-m) declined, whereas actual quantum yield (phi(PSII)) did not respond to O-3. O-3 exposure reduced grain yield in both cultivars. However, yield of Pegassos was more affected by O-3 exposure than yield of Astron, suggesting a higher O-3 sensitivity of Pegassos. The data presented in this manuscript indicate a need to test whether high-yield varieties such as Pegassos are particularly sensitive to O-3 exposure.