SUMMARYIt is evident that even outside the classical high ozone areas some plant species are at risk. In this study seedlings of five birch clones {Betula pendula Roth.) were exposed to a slightly elevated ozone level in an open-field experiment over two growing seasons. The ozone doses were 1-2 x (1991) and 1-5 x (1992) higher than the ambient. The clones were also fumigated with 150 nl 1 ' ozone for 24 d (12 h d"^) in a chamber experiment. They were found to differ in their susceptibility to ozone: ozone fumigation decreased the height growth and leaf biomass, and increased the amount of advanced visible injury in leaves of the most sensitive clone, but did not affect the height growth or amount of visible injury of the most tolerant clone. The other three clones were intermediate with respect to their sensitivity to ozone. In all clones, elevated O., concentrations increased diffusive resistance to water vapour but increased the stomatal density in the emerging leaves. The appearance of autumn colouririg was accelerated in the field experiments. The results support the conclusion that birch populations in Finland can be negatively affected by ozone. The effect is most likely in sensitive birch individuals during ozone episodes.
Arctic bramble (Rubus arcticus L.) and its hybrid (Rubus arcticus L. nothosubsp. stellarcticus G. Larsson) are both cultivated in Finland. Sugars and major organic acids were analysed in several arctic bramble clones and cultivars (n = 19) and arctic bramble hybrids (n = 5) by gas chromatography. The main sugar in the berries was sucrose, and the main organic acid was citric acid. The average total contents of sugars in the berries of arctic brambles and arctic bramble hybrids were 5.0 g (CV = 0.1) and 4.7 g (CV = 0.2) per 100 g of fresh weight, respectively. The average total contents of organic acids in the berries of arctic brambles and arctic bramble hybrids were 0.6 g (CV = 0.3) and 1.5 g (CV = 0.5) per 100 g of fresh weight, respectively. Changes in these compounds during the harvesting period were also studied in mixed samples. Moreover, the sensory properties of juices and jellies prepared from several arctic bramble clones were evaluated by quantitative sensory profiling. The sugar/acid ratio obtained from the chemical analyses of the berries was compared with the sensed sweetness and sourness of juices and jellies.
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