Growth, photosynthesis and ozone uptake of young beech (Fagus sylvatica L.) in response to different ozone exposures

Beech seedlings (Fagus sylvatica L.) were exposed to episodes of O-3 in env ironmentally controlled growth chambers during one growing season. Three tr eatments were applied: charcoal-filtered air, charcoal-filtered air with th e addition of 40 ppb O-3 for seven episodes of 5 days' duration (9000-1700 hours), and charcoal-filtered ail with the addition of 100 ppb O-3 for seve n episodes of 5 days' duration (9000-1700 hours). The accumulated exposure over a threshold of 40 ppb in the last treatment reached 13,911 ppb h. Thro ughout the growing season we measured growth as well as photosynthetic prop erties and related effects to external and calculated internal doses of O-3 , using stomatal conductance (g(s)) data. Growth, measured as diameter incr ement and biomass, was not significantly affected by the O-3 treatments. In the 100-ppb treatment, light-saturated CO2 assimilation rates and chloroph yll content were significantly reduced, and the chlorophyll fluorescence pa rameter F-v/F-m was significantly reduced at times of high uptake rates and coincided with strong reductions of assimilation rates. O-3 uptake was low ered in the 100-ppb treatment due to reduced g(s). There was serious visibl e damage by the end of the exposure period in the 100-ppb treatment, while the treatment with 40 ppb O-3 did not seem to cause any significant changes .