ASSESSING THE IMPACT OF OZONE ON PHOTOSYNTHESIS OF EUROPEAN BEECH (FAGUS-SYLVATICA L) IN ENVIRONMENTAL CHAMBERS

An exposure-response study with proportional-to-ambient ozone levels w as conducted in closed chambers on 3-year-old European beech (Fagus sy lvatica L.) of montane origin. The fumigation started in April 1990 an d lasted for a single growing season. Climate data and ozone concentra tions monitored at an experimental station of the Institute for Applie d Plant Biology, Schonenbuch, Switzerland were simulated in the exposu re chambers 12 days later (1O-3). To test exposure-response relations three additional treatments were applied, subambient (0.2O-3) and tw o proportionally increased ozone treatments (1.5O-3 and 2*O-3). The p hotosynthetic behaviour of the trees in August revealed the light reac tions to be less affected than parameters which are related to the dar k reactions of photosynthesis. Assimilation (A(350)), apparent carboxy lation efficiency (CE), and maximum photosynthetic capacity (A(2500)) were reduced with increasing ozone concentration. For the ozone respon se of CE and A(2500) 'Critical Levels' were calculated.