Effects of ozone exposure on growth and photosynthesis of beech seedlings (Fagus sylvatica)

The effects of ambient and elevated ozone levels on growth and photosynthesis of beech (Fagus sylvatica) were studied by exposing seedlings in open-top chambers for one growing season to three treatments: charcoal-filtered (CF), non-filtered (NF) and non-filtered air with addition of ozone (30 ppb ozone) on clear days for 8-10 h d^-1 (NF +). Ambient levels were relatively low and accumulated to an AOT40 (accumulated exposure over a threshold of 40 ppb) of 4055 ppb h (for the period 23 Apr-30 Sept). The NF + chambers received an AOT40 of 8880 ppb h. Throughout the growing season we measured growth and photosynthetic properties. The treatments did not cause strong effects: measurements of gas exchange (light-saturated assimilation rate, CO₂ and light-response curves) and chlorophyll fluorescence showed slight and mostly non-significant reductions of several parameters. No significant differences were found for growth, though in the NF + treatment (AOT40 8880 ppb h) the relative growth rate for diameter increment was at times reduced by 12% compared with the control treatment.