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We investigated the individual and interactive effects of moderately elevated CO2 (ambient air + 100 ppm) and/or O3 (40–50 ppb) on soil N cycling and microbial biomass N in a 3-year open-top chamber experiment conducted in meadow mesocosms. The results show that elevated O3 decreased the concentrations of mineral N and NH-N in the mesocosm soil in the last growing season (2004). Total N, NO-N, microbial biomass N, decomposition rate, potential nitrification and denitrification were not affected by elevated O3 and/or CO2. It is thus concluded that the proposed future ambient O3 and CO2 levels, such as used in this experiment, may not induce major changes in the below-ground N processes in N-poor northern European hay meadow ecosystems. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine whether a planted mesocosm mimics a natural habitat in terms of N2O and CH4 fluxes, soil characteristics and potential nitrification and denitrification activities. We compared mesocosms in unchambered open-field plots and in open-top chambers with nonfiltered ambient air with three natural meadows that had similar soil characteristics and species composition. The N2O fluxes in the mesocosms were very similar to the fluxes in the three natural meadows. There were no marked differences in potential nitrification and denitrification activities between the mesocosms and the natural meadows, either. Only the CH4 fluxes differed slightly between the mesocosms and some of the natural meadows. Therefore, it seems that the mesocosms compared rather well to natural habitats. The open-top chambers modified only the soil water content, the values being higher in the unchambered plots than in the chambered plots. These results thus suggest that the open-top chamber experiment enables estimates of greenhouse gas and potential activities of nitrifying and denitrifying bacteria in unfertilized Finnish meadows, in spite of the chamber effects on the soil water content. [ABSTRACT FROM AUTHOR]

Data from two Swedish and one Finnish open-top chamber experiments were combined to investigate effects of ozone exposure on potato (Solanum tuberosum L.) tuber content of starch, sucrose, fructose, glucose, malic, citric and ascorbic acids. The glucose, fructose and malic acid concentrations showed strong negative correlations with ozone exposure, while citric acid, consistently increased with ozone exposure. No ozone effects could be demonstrated on starch, sucrose or ascorbic acid concentrations. It is discussed to what extent the changes found in potato tuber composition can be explained in terms of ozone effects on tuber maturity. Ozone exposure was expressed as the accumulated exposure over a cut-off concentration of 40 nmol mol−1 (AOT40) and as the accumulated uptake of ozone over an ozone uptake rate threshold of 7 nmol m−2 s−1 (CUO 7). The difference in ability of the exposure indices to explain observed effects was small. [ABSTRACT FROM AUTHOR]

Catalase (EC 1.11.1.6) activity (both total and specific activity) of particulate fractions of needles of Norway spruce [ Picea abies (L.) Karst.] was elevated approximately 2-fold following exposure of trees to 60-70 μg/m of ozone during the growing season compared to trees receiving charcoal filtered air (about 15 μg/m ozone). Measurements were from homogenates fractionated into particulate and soluble (supernatent) activities. In contrast, the catalase activity of the supernatant was unchanged in response to ozone treatment. Catalase activity declined as the needles aged comparing current, 1-, and 2-year needles but the ozone-induced increment remained constant. Electron microscope cytochemistry using peroxidatic coupling with 3,3′-diaminobenzidine carried out in parallel, revealed catalase-containing peroxisomes both in situ and in the particulate fractions analyzed for catalase activity. The tissue volume occupied by peroxisomes in response to needle age and ozone appeared to vary approximately in proportion to the measured catalase activity. Overall cytochemical reactivity for catalase declined with needle age, but, for all years, was greater in needles of trees receiving air supplemented with ozone compared to those of trees receiving charcoal filtered air. [ABSTRACT FROM AUTHOR]