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Ozone may affect leaf photosynthesis even before visible symptoms become apparent. This study had the objective to test several parameters of chlorophyll fluorescence and leaf gas exchange for their usefulness as indicators of latent ozone injury in the field. Container‐grown apple trees (Malus domestica Borkh. cv. Golden Delicious) were exposed to four different ozone levels in open‐top chambers. Identical leaves were analyzed in fixed‐time intervals for the characteristics of fast fluorescence induction kinetics in vivo. By using high‐time resolution, characteristic parameters describing the early photochemical events could be calculated according to the JIP‐test. Parameters responsive to the different ozone treatments showed clear dependence on the accumulated ozone dose. Ozone exposure immediately preceding the measurements was more important for the extent of the physiological effects than the total accumulated ozone dose. The most sensitive parameters were the turnover number N (indicating how many times QA has to be reduced for full reduction of all acceptors; positively correlated to ozone dose) and D0, the density of reaction centres per leaf area (negatively correlated to ozone dose). Most parameters analyzed showed clearer responses to ozone on the adaxial than on the abaxial surface of the leaf. Changes in the parameter N were better correlated to ozone doses with low cut‐offs (AOT00 and AOT20), whereas changes in D0 and in the specific electron fluxes per reaction centre were mainly influenced by ozone doses with high cut‐offs (AOT80 and AOT100). Leaf gas exchange analyses revealed a higher ozone sensitivity in carboxylation efficiency than in light utilization efficiency and in the rate of light‐saturated net photosynthesis. All ozone‐induced photosynthetic effects were observed in leaves showing no sign of visible leaf injury. This study identified fluorescence parameters that could be useful for rapid monitoring and early detection of latent leaf injury by ozone.

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Ice cover of the two Central European steppe lakes, Lake Balaton (Hungary) and Lake Neusiedl (Austria/Hungary), is characterized by high interannual variability (mean ice duration ± s.d.: 44±26 days and 73±28 days, respectively). For both lakes, a trend towards shorter ice duration and earlier ice-off can be observed in the 86 and 81 year data records, respectively. For Lake Neusiedl, significant trends for ice-on (+2.3 days decade −1 ), ice-off ( −1.8 days decade −1 ) and ice duration ( −3.1 day decade −1 ) are detected. At Lake Balaton, however, trends for ice-on (0 day decade −1 ), ice-off ( −0.7 days decade −1 ) and ice duration ( −1.2 days decade −1 ) are not significant. The temporal trends have accelerated for Lake Neusiedl in the past 60 years (ice duration −5.6 days decade −1 ). The variability of the ice parameters has increased during the 80 year observation period for Lake Neusiedl, but not for Lake Balaton. The number of melt-refreeze cycles at Lake Balaton increased at first, but then decreased during the last 20 years at both lakes.Warming trends in mean surface water temperatures for all seasons are more distinct than temporal trends of mean air temperatures. Increases of winter air temperature by 1°C are related to an ice-on delay, a decrease in ice duration (Lake Balaton: −12 days°C −1 , R 2 =0.72; Lake Neusiedl: −11 day°C −1 , R 2 =0.54) and an earlier ice-off. Snow cover, wind speed, and solar radiation are also related to ice dates.Mediterranean Oscillation and the North Atlantic Oscillation show significant relationships with ice phenology at both lakes whereas the East Atlantic teleconnection pattern only is related to ice characteristics of Lake Neusiedl.

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