Young trees of European beech (Fagus sylvatica) acclimated for one growing season to ambient (c. 367 µl l −" ) or elevated CO # levels (c. 660 µl l −" ) were exposed during the subsequent year to combinations of the same CO # regimes and ambient or twice-ambient ozone (O $ ) levels (generated from the database of a rural site). By the end of June, before the development of macroscopic leaf injury, the raised O $ levels had not affected the light and dark reactions of photosynthesis. However, acclimation to elevated CO # had resulted in lowered chlorophyll and nitrogen concentrations, whereas photosynthetic performance, examined over a wide range of parameters from light and dark reactions, remained unchanged or showed only slight reductions (e.g. apparent electron transport rate, ETR ; apparent quantum yield of CO # gas exchange, Φ CO# ; apparent carboxylation efficiency, CE ; and photosynthetic capacity at light and CO # saturation, PC). In August, after the appearance of leaf necroses, plants grown under ambient CO # and twice-ambient O $ conditions declined in both the photosynthetic light reactions (optimum electron quantum yield, F v \F m , non-photochemical energy quenching, NPQ, reduction state of Q A , apparent electron quantum yield, Φ PSI I, maximum electron transport rates) and the dark reactions as reflected by CE, Φ CO# , as well as the maximum CO # uptake rate (i.e. PC). CE, Φ CO# and PC were reduced by c. 75, 40 and 75%, respectively, relative to plants exposed to ambient CO # and O $ levels. By contrast, plants exposed to twice-ambient O $ and elevated CO # levels maintained a photosynthetic performance similar to individuals grown either under ambient CO # and ambient O $ , or elevated CO # and ambient O $ conditions. The long-term exposure to elevated CO # therefore tended to counteract adverse chronic effects of enhanced O $ levels on photosynthesis. Possible reasons for this compensatory effect in F. sylvatica are discussed.

Young trees of European beech (Fagus syl7atica L.) were phate carboxylase/oxygenase activity, while the summer and exposed in a phytotron to different levels of ozone and CO 2 early autumn harvests showed strong reductions in these under the climatic simulation of one vegetation period. High parameters. Only phosphoenolpyruvate carboxylase (PEPozone levels were simulated similar to high ozone concentra-case) activity remained higher under high ozone. The effects of high CO 2 appeared in general as a small stimulation in tion in the field (up to 110 ppb), while CO 2 was added as 300 ppm to the present level of ca 380 ppm. Our study describes enzyme activity like PEPcase in spring. However, with indifferent aspects of photosynthesis from the leaf level to the creasing time of fumigation, reductions of all parameters were observed. Especially chlorophylls showed strong reduc-reactions of selected thylakoid components at different hartions under high CO 2 . The combined treatment with high vest times during growth of the beech trees under the different fumigation regimes. Ozone effects appeared in the first weeks ozone plus high CO 2 resulted mostly in an amelioration of the of the treatment as a stimulation of chlorophyll fluorescence negative ozone effects, although control levels were not (F v /F m ), in oxygen production and in ribulose-1,5-bisphos-reached.

To test the involvement of ethylene in mediating ozoneinduced cell death and leaf loss in European beech ( Fagus sylvatica L.), tree seedlings were exposed to proportionally increased or decreased field ozone levels for up to 6 months. Ozone treatment caused cell death and accelerated leaf loss at higher than ambient levels, but had only minor effects at ambient and no effects at subambient ozone levels. The emission of ethylene, the levels of its precursor, 1-aminocyclopropane-1-carboxylate (ACC), and mRNA levels of specific ACC synthase ( FS-ACS2 ) and ACC oxidase ( FS-ACO1 ) isoforms showed a persistent increase and preceded cell death by approximately 2 weeks. Inhibition of ethylene biosynthesis led to reduced lesion formation whereas application of ACC accelerated ozoneinduced cell death and leaf loss. Similar results were obtained when adult beech trees were exposed to 2 ¥ ¥ ¥ ¥ ozone by a whole tree free-air canopy exposure system. The results suggest a role of ethylene in amplifying ozone effects under field conditions in this major European broad-leaved tree species.

Internal transcribed spacer (ITS) sequences of the rDNA repeat unit of Heterobasidion annosum were used to design specific primers for the detection and quantification of this important forest pathogen by polymerase chain reaction (PCR). Specificity of detection was cross‐checked against a variety of other fungi (saprophytes, root pathogens, mycorrhizal fungi) which may occur in the same environment. As little as 1 pg fungal DNA (equiv. to 10–40 genomes) could be detected in 200 ng spruce root DNA (from 1 mg fresh spruce root). The Heterobasidion‐specific primers allowed simultaneous detection of Armillaria spp. in multiplex PCR. The method was successfully applied to increment cores of Norway spruce from the forest region Tharandter Wald (Saxonia, Germany), Oberbärenburg (East Ore Mountains, Saxonia) and Oberschleissheim (north of Munich, Bavaria).