The effect of ozone fumigation over one season on photosynthetic processes of Quercus robur seedlings

Quercus robur saplings were exposed to elevated O-3 (80 nmol mol(-1)) in hemispherical glasshouses for one growing season in order to assess the effects of this pollutant on photosynthesis. Measurements of chlorophyll fluorescence induction kinetics in mid-summer showed that plants exposed to both control O-3 (20 nmol mol(-1)) and elevated O-3 treatments experienced significant photoinhibition of photosynthesis. Elevated O-3 increased photoinhibition. Al the end of the summer, photosynthetic CO2 uptake, measured at either light saturation or under light-limiting conditions, was not significantly different between plants from the two O-3 treatments. Although the maximum rate of carboxylation velocity, as estimated from the response of CO2 uptake to intercellular CO2 concentration, the maximum quantum efficiency and the maximum rate of electron transport measured in vivo were decreased by O-3 exposure, the responses differed between plants and, overall, the decreases were not statistically significant. The results suggest that O-3 levels that are at present reached for a few days during photochemical episodes in the summer are not sufficient to cause measurable lasting damage to photosynthetic CO2 uptake in oak saplings assessed over one growing season.