The effects of experimentally elevated O3 on soil respiration rates, standing fine-root biomass, fine-root production and δ13C signature of newly produced fine roots were investigated in an adult European beech/Norway spruce forest in Germany during two subsequent years with contrasting rainfall patterns. During humid 2002, soil respiration rate was enhanced under elevated O3 under beech and spruce, and was related to O3-stimulated fine-root production only in beech. During dry 2003, the stimulating effect of O3 on soil respiration rate vanished under spruce, which was correlated with decreased fine-root production in spruce under drought, irrespective of the O3 regime. δ13C signature of newly formed fine-roots was consistent with the differing gs of beech and spruce, and indicated stomatal limitation by O3 in beech and by drought in spruce. Our study showed that drought can override the stimulating O3 effects on fine-root dynamics and soil respiration in mature beech and spruce forests. Drought has the capacity to override the stimulating ozone effect on soil respiration in adult European beech/Norway spruce forest.

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.

Stomatal O3 fluxes to a mixed beech/spruce stand (Fagus sylvatica/Picea abies) in Central Europe were determined using two different approaches. The sap flow technique yielded the tree-level transpiration, whereas the eddy covariance method provided the stand-level evapotranspiration. Both data were then converted into stomatal ozone fluxes, exemplifying this novel concept for July 2007. Sap flow-based stomatal O3 flux was 33% of the total O3 flux, whereas derivation from evapotranspiration rates in combination with the Penman-Monteith algorithm amounted to 47%. In addition to this proportional difference, the sap flow-based assessment yielded lower levels of stomatal O3 flux and reflected stomatal regulation rather than O3 exposure, paralleling the daily courses of canopy conductance for water vapor and eddy covariance-based total stand-level O3 flux. The demonstrated combination of sap flow and eddy covariance approaches supports the development of O3 risk assessment in forests from O3 exposure towards flux-based concepts.

Malondialdehyde (MDA), a product of lipid peroxidation and biomarker of oxidative stress, is measured over the long term in spruce Picea abies needles under real conditions in three Czech mountain border areas. The trends presented collate the MDA content in spruce needles with ambient ozone, temperature and precipitation as casual, and defoliation as a subsequent factor for the period 1994-2006. We have found the overall decreasing trends in MDA and defoliation. The highest MDA and defoliation are recorded in the Jizerske, the lowest in the Krusne hory Mts. Out of the examined variables the MDA is predicted best by mean temperature in vegetation season, median of O3 concentrations and AOT40; these three variables account for 34% of MDA1 and 36% of MDA2 variability. Our hypothesis that higher ambient O3 exposure results in higher MDA contents in P. abies needles under real conditions has not been approved.

Here we synthesize key findings from a series of experiments to gain new insight on inter-plant competition between juvenile beech (Fagus sylvatica) and spruce (Picea abies) under the influence of increased O3 and CO2 concentrations. Competitiveness of plants was quantified and mechanistically interpreted as space-related resource investments and gains. Stable isotopes were addressed as temporal integrators of plant performance, such as photosynthesis and its relation to water use and nitrogen uptake. In the weaker competitor, beech, efficiency in space-related aboveground resource investment was decreased in competition with spruce and positively related to Δ13C, as well as stomatal conductance, but negatively related to δ18O. Likewise, our synthesis revealed that strong belowground competition for water in spruce was paralleled in this species by high N assimilation capacity. We suggest combining the time-integrative potential of stable isotopes with space-related investigations of competitiveness to accomplish mechanistic understanding of plant competition for resources. Combination of space-related concepts of competitiveness with stable isotopes has potential to clarify mechanisms of competition.

A long-term hydrological and water chemistry research was conducted in three experimental microbasins differing in land cover: (1) a purely agricultural fertilized microbasin, (2) a forested microbasin dominated by Carpinus betulus (European hornbeam), and (3) a forested microbasin dominated by Picea abies (L.) (Norway spruce). The dissolved inorganic nitrogen (DIN: NH ₄ ⁺ , NO ₂ ⁻ , NO ₃ ⁻ ) budget was examined for a period of 3 years (1991-1993). Mean annual loads of DIN along with sulfate SO ₄ ²⁻ and base cations Ca²⁺, Mg²⁺, Na⁺, K⁺, and HCO ₃ ⁻ were calculated from ion concentrations measured in stream water, open-area rainfall, throughfall (under tree canopy), and streamwater at the outlets from the microbasins. Comparison of the net imported/exported loads showed that the amount of NO ₃ ⁻ leached from the agricultural microbasin is ∼3.7 times higher (43.57 kg ha⁻¹ a⁻¹) than that from the spruce dominated microbasin (11.86 kg ha⁻¹ a⁻¹), which is a markedly higher export of NO ₃ ⁻ compared to the hornbeam dominated site. Our analyses showed that land cover (tree species) and land use practices (fertilization in agriculture) may actively affect the retention and export of nutrients from the microbasins, and have a pronounce impact on the quality of streamwater. Sulfate export exceeded atmospheric rainfall inputs (measured as wet deposition) in all three microbasins, suggesting an additional dry depositions of SO ₄ ²⁻ and geologic weathering.

The fluxes of N-NO ₃ ⁻ , N-NH ₄ ⁺ , S-SO ₄ ²⁻ , Na⁺, K⁺, Ca²⁺ and Mg²⁺ from bulk precipitation to throughfall, stemflow and soil water surface flows were studied during 1999-2003 in planted Norway spruce forest stands of different ages (11, 24, 91 and 116 years in 1999). Also, runoff from the corresponding Potok Dupniański Catchment in the Silesian Beskid Mts was studied. N deposition was above the critical load for coniferous trees. The interception increased with stand age as well as leaf area index and so did the leaching from the canopy of almost all the analysed elements, but especially S-SO ₄ ²⁻ , H⁺ and K⁺. The nutrient fluxes varied with age of the spruce stands. Throughfall showed a high amount of S and of the strong acids (S-SO ₄ ²⁻ and N-NO ₃ ⁻ ) deposited to the soil, especially in older spruce age classes. Decomposition of organic matter caused a rise in water acidity and an increase in the concentrations of all the analysed ions; the leaching of minerals, however, was low (under 1%). The horizontal soil water flow showed an increase in the amount of water and amount of ions and contributed to a further decrease of pH at the soil depth of 20 cm. Element concentrations and their amounts increased with water penetrating vertically and horizontally on the slopes. Considerable amounts of ions, especially S and alkaline cations, were carried beyond the reach of the root system and then left the catchment. In the long term, these mineral losses will adversely affect health and growth of the spruce stands, and the increased acidity with stand age will presumably have negative effects on the runoff water ecosystem.

Dissolved organic nitrogen (DON) plays an important ecological role in forest ecosystems, and its concentration is related to that of dissolved organic carbon (DOC). We investigated DON concentrations and ratios of DOC to DON in throughfall and soil waters in 16 Norway spruce and two Scots pine forest stands sampled at weekly intervals between 1996 and 2006. The stands are all included in the ICP Forests Level II monitoring program and are located throughout Norway. DON concentrations were significantly and positively related to DOC concentrations in throughfall (r ² = 0.72, p < 0.0001) and soil water at 5, 15, and 40 cm (r ² = 0.86, 0.32, and 0.84 and p < 0.0001, 0.04, and <0.0001, respectively). At most sites, the annual median DOC/DON ratio in throughfall ranged from 20.3 to 55.5, which is lower than values in soil water, which ranged from 24.5 to 81.3, gradually decreasing with soil depth. DON concentrations varied seasonally in throughfall at many plots and in soil water at 5-cm depth at one plot only, with higher values in the growing season, but there was no noticeable seasonality at greater depth. The ratios of DOC/DON in soil water were significantly positively related to the C/N ratio in soil at the same depth. Above-ground litter input was the main factor having a significant, negative relationship to DOC/DON in soil water at all depths studied. This might reflect the effect of site conditions on both DOC/DON ratios and litter quantity.