Beech (Fagus sylvatica) response to ozone exposure assessed with a chlorophyll a fluorescence performance index

This paper describes a relationship between ozone exposure, biomass, visual symptoms and a chlorophyll a fluorescence performance index for young beec h trees (Fagus sylvatica). The plants were exposed to four levels of ozone in open-top fumigation chambers (50, 85, 100% of ambient, and 50% of ambien t + 30 nl l(-1) ozone) that fluctuated in parallel with ambient ozone durin g a single growing season. The trees were fumigated in the four treatments with ozone levels corresponding to an AOT40 (accumulated exposure above a t hreshold of 40 nl l(-1)) of 0.01, 3.35, 7.06 and 19.70 mu l l(-1) h, respec tively. Highly significant differences were found between the 50% of ambien t + 30 nl l(-1) ozone treatment and all other treatments, with a 70.5% redu ction in primary photosynthetic performance, as measured with the PI index. The reduction of the PI values demonstrated a high correlation with visual symptom development (r(2) = 0.98), and by the end of September with biomas s loss (r(2) = 0.99). A significant ozone exposure-response relationship wa s found between AOT40 and primary photochemistry (r(2)=0.97). Thus, analysi s of PI provides an alternative method for regional monitoring of tree heal th within the context of the currently employed AOT40. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.