Responses to ozone in 12 provenances of European beech (Fagus sylvatica): genotypic variation and chamber effects on photosynthesis and dry-matter partitioning

Seedlings of 12 provenances of European beech (Fagus sylvatica) were expose d to ambient, non-filtered air (NF) or NF + 50 nl l(-1) ozone (NF50) for 8 h d(-1) in open-top chambers (OTCs), from 1 June to 1 October 1995. In 1996 exposure was continued from 31 May to 1 October at four levels: charcoal-f iltered air (CF), NF, NF50 and NF + 100 nl l(-1) ozone (NF100). Provenances were grown for both seasons in outside reference plots. All treatments wer e replicated. Ozone did not affect gas exchange in the provenances until la te in the second season. NF100 reduced photosynthesis by 18% in August 1996 compared to CF. In September, photosynthesis vc-as reduced by 22%, in NF50 and by 29% in NF100. After two seasons, ozone reduced the root:shoot ratio by 24% when comparing CF and NF100; this was caused by reductions in the r oot biomass. Ozone did not affect height growth or stem diameter, and there mere no ozone x provenance interactions for any growth parameter. There wa s, however, a significant ozone x provenance interaction for photosynthesis , showing northwest European provenances to be more sensitive to ozone than southeast European provenances when comparing dose-response estimates. Thi s is interpreted in terms of genetic adaptation of the photosynthetic appar atus to regional growing conditions. Seedlings in the chambers grew 45%, ta ller, and had 28% more shoot biomass and 29%, smaller root biomass, resulti ng in a 44% reduction of root:shoot ratios compared to seedlings outside. I ncreased temperature and decreased PAR inside the chambers relative to the outside were probably the main causes for the differences. The magnitude of the chamber effects in OTCs raises doubts about conclusions drawn from ozo ne exposures in such chambers. This and previous ozone experiments with OTC s may have reached inaccurate conclusions concerning the size of ozone resp onses due to chamber effects.