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Effects of elevated N deposition on forest aboveground biomass were evaluated using long-term data from N addition experiments and from forest observation plots in Switzerland. N addition experiments with saplings were established both on calcareous and on acidic soils, in 3 plots with Fagus sylvatica and in 4 plots with Picea abies. The treatments were conducted during 15 years and consisted of additions of dry NH4NO3 at rates of 0, 10, 20, 40, 80, and 160 kg N ha(-1) yr(-1). The same tree species were observed in permanent forest observation plots covering the time span between 1984 and 2007, at modeled N deposition rates of 12-46 kg N ha(-1) yr(-1). Experimental N addition resulted in either no change or in a decreased shoot growth and in a reduced phosphorus concentration in the foliage in all experimental plots. In the forest, a decrease of foliar P concentration was observed between 1984 and 2007, resulting in insufficient concentrations in 71% and 67% of the Fagus and Picea plots, respectively, and in an increasing N:P ratio in Fagus. Stem increment decreased during the observation period even if corrected for age. Forest observations suggest an increasing P limitation in Swiss forests especially in Fagus which is accompanied by a growth decrease whereas the N addition experiments support the hypothesis that elevated N deposition is an important cause for this development.

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RESUMEN

Epidemiological analysis of sequential growth data may be a tool in assessing ozone sensitivity of mature trees. Annual shoot growth of mature Fagus sylvatica in 83 Swiss permanent forest observation plots and of Picea abies in 61 plots was evaluated for 11 and 8 consecutive years, respectively, using branches harvested every 4 years. The data were assessed as annual deviation from average growth and related to fructification, ozone, meteorological parameters, and modelled soil water content using a mixed linear model. In beech, a significant association between ozone and shoot growth was observed which corresponded to a 7.4% growth reduction between 0 and 10 ppm h AOT40 (accumulated ozone over threshold 40). This is in the same order of magnitude as the response observed in experiments with seedlings. No interaction was found between ozone and drought parameters. In Norway spruce, shoot growth was neither associated with ozone nor with drought.

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Root length of naturally grown young beech trees (Fagus sylvatica L.) was investigated in 26 forest plots of differing base saturation and nitrogen deposition. The relative length of finest roots (<0.25 mm) was found to decrease in soils with low base saturation. A similar reduction of finest roots in plots with high nitrogen deposition was masked by the effect of base saturation. The formation of adventitious roots was enhanced in acidic soils. The analysis of 128 soil profiles for fine roots of all species present in stands of either Fagus sylvatica L., Picea abies [Karst.] L. or both showed a decreased rooting depth in soils with < or =20% base saturation and in hydromorphic soils. For base rich, well drained soils an average rooting depth of 108 cm was found. This decreased by 28 cm on acidic, well drained soils. The results suggest an effect of the current soil acidification in Switzerland and possibly also of nitrogen deposition on the fine root systems of forest trees.

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We examined manganese uptake and translocation in 30-year-old silver fir trees (Abies alba Mill.) showing severe symptoms of needle chlorosis by analyzing both xylem and phloem sap of shoots and an extract of root sap originating from both xylem and phloem elements. Manganese concentrations in shoot xylem and phloem sap were significantly lower in chlorotic trees than in neighboring healthy trees. The Mn concentration of root sap was also lower in these Mn-deficient trees than in healthy trees, indicating reduced Mn uptake by Mn-deficient trees. Although Mn deficiency had no effect on the Mn concentration of whole roots, separation of root tissue into root cortex and stele (wood) suggested impaired translocation of Mn from the cortex to the stele in Mn-deficient trees. Triphenyltetrazolium chloride (TTC) tests indicated that there was no decrease in reducing capacity of the fine roots (< 1 mm in diameter) of Mn-deficient trees. Fine roots of Mn-deficient trees contained significantly more organic acids than fine roots of healthy trees, including increased concentrations of malic, quinic, trans-acontic and formic acid; however, concentrations of pyruvic and acetic acid were lower than in fine roots of healthy trees. The total amounts of organic acids in the rhizospheric soil were similar for healthy and Mn-deficient trees. Pyruvic acid concentration was significantly increased in the rhizospheric soil of Mn-deficient trees, and concentrations of simple aliphatic acids like formic and acetic acid also tended to be higher in the rhizospheric soil of Mn-deficient trees. Both pH and water content were higher in bulk soil and rhizospheric soil around Mn-deficient trees compared with soil around healthy trees. Although lower concentrations of exchangeable Mn were found in the soil around Mn-deficient trees, the active Mn concentration (sum of exchangeable and reducible Mn) did not differ between healthy and Mn-deficient trees. A considerable proportion of manganese was in an oxidized form in the soil around Mn-deficient trees.

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The effect of unfiltered versus filtered air was tested on tree seedlings at different sites with prevailing ozone pollution, at different altitudes. Growth and biomass data from different experiments were evaluated in relation to ozone dose above 40 nl l-1 during the exposure time. In beech (Fagtis sylvatica L.), biomass was significantly correlated with ozone dose whereas shoot length was not. There was no change in shoot/root ratio but there were more significant reductions in fine root biomass than in shoot biomass. The effect of ozone was cumulative within the duration of the experiments, i.e. from a few months to three years. A cumulative dose of 7 µl 1-1 h > 40 nl l-1 Per growing season, calculated for 24 h day-1 , corresponded to a 10% biomass reduction within three years. Seedlings grown in unfiltered air also exhibited much more severe symptoms of frost injury following a cold winter with rapid temperature change. Laboratory experiments suggest that winter desiccation may have played a more important role than low temperatures, but that medium frost temperatures may cause more latent injuries in seedlings exposed to ambient air. Water loss of detached leaves from unfiltered air was significantly higher later m the season. Both increased chlorosis and premature leaf fall were observed in the beech seedlings grown in unfiltered air, but in different years. The biomass of spruce [Picea abies (L.) Karst.] showed a tendency towards a reduction, but this was not significant within the dose range tested. Three years of fumigation, however, caused increased chlorosis also in the spruce seedlings. Tests with low temperatures suggest that the vitality of the spruce seedlings during winter may also be impaired by the ambient air pollution.

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Beech seedlings (Fagus sylvatica L.) were sprayed with acidic or ammonium-rich solutions of different concentrations, 10-3 or 10-5 mol l-1 H+ or NH4 + . Whilst the leaching of Ca and Mg was increased by the more acid treatment, the K leaching was decreased. On the other hand, the concentrated NH4 + mist led to a substantial increase in the leaching of K. As a consequence of the greater uptake of cations due to their leaching, more protons were released to the nutrient solution and into the rhizosphere of potted plants. Increased transpiration was observed following the application of acidic mist to the plants in nutrient solution but decreased stomatal diffusive resistance of potted plants was detected only at night. Acid mist caused changes in stomatal behaviour that were responsible for a rapid and greater water loss of detached leaves.