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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    FEBS Letters 171 (1984), S. 5-8 
    ISSN: 0014-5793
    Keywords: Adenovirus ; DNA replication in vitro ; Reconstitution ; Small RNA
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1608-3105
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 3
    ISSN: 1573-5052
    Keywords: Air pollution ; Decline of phanerogamic species ; Dose-effect model ; Epiphytic lichens ; Habitat destruction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In The Netherlands the decline of some phanerogamic species cannot be readily explained from obvious factors such as lowering of the groundwater table, eutrophication or land reclamation. For a number of species the hypothesis was tested that the decline is partly due to air pollution. A two-factor model was made in which decline is accounted for by (a) habitat destruction assessed from topographic maps and (b) air pollution measured as the SO2 95-percentile over the winter period 1978/1979. Effects of both factors were assumed to follow a sigmoid dose-effect curve. For a number of species decline proved to be significantly correlated with air pollution. These are notably species from the syntaxon Violion caninae. A comparison was made with results obtained for epiphytic lichens. It appears that for some phanerogamic species sensitivity is about the same as for moderately sensitive lichens.
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  • 4
    ISSN: 0165-2370
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
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  • 5
    ISSN: 1573-5036
    Keywords: air pollution ; ammonium sulphate ; Antennaria dioica ; Arnica montana ; Glomus fasciculatum ; heathland vegetation ; Hieracium pilosella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Three heathand species, Antennaria dioica, Arnica montana and Hieracium pilosella, were artificially rained with ammonium sulphate solutions at increasing concentrations in a greenhouse experiment. The same species were also artificially rained with increasing ammonium sulphate solutions under field conditions. Dry weights of the plants in the field experiments did not change with increasing ammonium sulphate applications. Nor did the dry weights of plants in the greenhouse experiments change with increasing ammonium sulphate concentrations, except for Arnica montana, which showed an increase in dry weight. VAM infection percentage of Antennaria dioica increased in both the greenhouse and the field experiment. The results of the field experiment show that VAM infection rates are reduced after two years of artificial rain in the plant species Arnica montana, which grows naturally under nutrient poor conditions and is presently declining in its natural habitat in the Netherlands. In the greenhouse experiment, VAM infection of Arnica montana did not change with increasing ammonium sulphate concentrations. VAM infection rates of Hieracium pilosella, which presently is not declining, did not change with increasing ammonium sulphate concentrations.
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  • 6
    ISSN: 1573-5036
    Keywords: decline of Arnica montana ; heathland vegetation ; pH ; soil acidification ; VAM ; vesicular-arbuscular mycorrhiza
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A greenhouse experiment was carried out to determine whether the decline of Arnica montana L. in heathland vegetation in the Netherlands could be caused by a detrimental effect of soil acidification on vesicular-arbuscular mycorrhiza of this species. Arnica montana and two non-declining species from the same habitat, Hieracium pilosella L. and Deschampsia flexuosa (L.) Trin., were grown with and without the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum (Thaxter sensu Gerdemann) Gerd. and Trappe in pots with an extremely nutrient-poor, sandy soil. They were percolated weekly with nutrient solution with different pH values, viz. 5.5, 4.5, 3.5 and 2.5. At intervals of three weeks and up to 12 weeks, measurements were made on growth, nutrient uptake and VAM infection. In the most acid treatments growth and nutrient uptake were reduced in all species. VAM infection decreased only slightly with decreasing pH of the treatments. Without VAM, Arnica montana died and Hieracium pilosella hardly grew at the most acid treatments. Therefore it is concluded that VAM decreased the stress caused by the most acid treatments. Leachate from the most acid treatment had a pH of approximately 4, and contained considerable amounts of aluminium, dissolved from the solid phase of the soil. This might have played a role in the detrimental effects on the plants in the case of the most acid treatment. No evidence was found in this experiment that the decline of Arnica montana was due to detrimental effects of soil acidification on VAM of this species.
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  • 7
    ISSN: 1573-5036
    Keywords: carbon mineralization ; microbial biomass ; 15N ; nitrogen mineralization ; temperature effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effects of temperature on N mineralization were studied in two organic surface horizons (LF and H) of soil from a boreal forest. The soil was incubated at 5 °C and 15 °C after adding 15 N and gross N fluxes were calculated using a numerical simulation model. The model was calibrated on microbial C and N, basal respiration, and KCl-extractable NH4 +, NO3 −, 15NH4 + and 15 NO3 −. In the LF layer, increased temperature resulted in a faster turnover of all N pools. In both layers net N mineralization did not increase at elevated temperature because both gross NH4 + mineralization and NH4 + immobilization increased. In the H layer, however, both gross NH4 + mineralization and NH4 + immobilization were lower at 15 °C than at 5 °C and the model predicted a decrease in microbial turnover rate at higher temperature although measured microbial activity was higher. The decrease in gross N fluxes in spite of increased microbial activity in the H layer at elevated temperature may have been caused by uptake of organic N. The model predicted a decrease in pool size of labile organic matter and microbial biomass at elevated temperature whereas the amount of refractory organic matter increased. Temperature averaged microbial C/N ratio was 14.7 in the LF layer suggesting a fungi-dominated decomposer community whereas it was 7.3 in the H layer, probably due to predominance of bacteria. Respiration and microbial C were difficult to fit using the model if the microbial C/N ratio was kept constant with time. A separate 15N-enrichment study with the addition of glucose showed that glucose was metabolized faster in the LF than in the H layer. In both layers, decomposition of organic matter appeared to be limited by C availability.
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  • 8
    ISSN: 1573-515X
    Keywords: acid rain ; atmospheric deposition ; chalk grassland ; simulation model ; throughfall ; sulphur cycling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Sulphate fluxes in bulk deposition, throughfall and soil solution were monitored during two years, and integrated within a model describing the cycling of S in a chalk grassland ecosystem. Throughfall fluxes were strongly determined by interceptive properties of the grassland canopy. Seasonal variation in Leaf Area Index resulted in dry deposition velocities for SO2 varying between 0.1 cm.s−1 (snow cover, almost no aerodynamic resistance) to 0.9–1.8 cm.s−1 in periods with a fully developed canopy. On an annual basis net canopy exchange (assimilation of SO2 minus foliar leaching) was estimated to be −15% of net throughfall. Simulated soil solution concentrations, being the result of throughfall input, leaching, adsorption, biomass uptake and mineralization, closely fitted actual values (r 〉 0.92; p 〉 0.001). Actual and simulated leaching were 1.74 ± 0.03 and 2.00 keq.-ha−1.yr−1, respectively. Sulphur budgets for the soil showed net accumulation from April to October and net losses from October to April. Annual budgets for the ecosystem showed atmospheric input (2.02keq.ha−1.yr−1) and actual output (2.05keq.ha−1.yr−1) to be almost balanced. Apart from increased soil solution concentrations, additional input of sulphate (3.55 keq.ha−1.yr−1) to experimental plots resulted in additional accumulation in the ecosystem of 0.62 keq.ha−1.yr−1
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  • 9
    ISSN: 1573-2932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Lysimeter experiments were used to determine atmospheric input to grassland canopies. The combined effect of interception deposition + mineral weathering + mineralization was calculated from input/output budgets. Four types of lysimeters were used, either filled with very pure quartz sand or chalk grassland soil, and either without vegetation or planted with Brachypodium pinnatum (L.) Beauv., Combination of budgets for these four types of lysimeters yielded separate estimates of interception deposition and mineral weathering + mineralization. Ratios between total deposition and bulk deposition were 1.74 and 1.93 for N and S, respectively. Sources and sinks of H+ for lysimeters with chalk grassland soil and planted with Brachypodium (abbrev. CP-lysimeters) were about 10 times larger than for lysimeters without plants and filled with quartz sand. The contribution of atmospheric input to total H+-sources was 80% for bare lysimeters filled with quartz sand, and only 12% for CP-lysimeters. Bulk deposition and total atmospheric deposition of N was 1.25 and 2.18 kmol ha−1 yr−1, respectively, whereas N mineralization of chalk grassland soil yielded 1.62 kmol ha−1 yr−1, ‘Acid rain’ has only a minor influence on H+-transformations within a chalk grassland ecosystem, but N cycling is seriously affected by atmospheric input.
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  • 10
    ISSN: 1573-2932
    Keywords: coniferous ecosystems ; Douglas fir ; 15N ; NICCCE ; NITREX ; nitrogen ; simulation model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract For a Douglas fir forest ecosystem subjected to an experimental decrease in nitrogen (N) deposition, N dynamics were simulated using the dynamic simulation model NICCCE. Meteorological driving variables and N concentrations in throughfall were input to the model, that simulated results of a 15N tracer experiment, C and N concentrations in the soil, soil water chemistry and tree biomass. Four years of ambient N deposition, followed by four years of N deposition manipulations by means of a roof construction beneath the forest canopy, were modelled. Simulation of this second period was performed for a high-N treatment (37 kg N ha-1 yr-1) and a low-N treatment with throughfall-N at natural background level (6 kg N ha-1 yr-1). Calibration and model performance is discussed and compared to results of field experiments. The quick response of soil water chemistry after lowering N deposition and the 15N tracer signal observed in soil water at 90 cm soil depth, were simulated closely by the calibrated model. 15NH4-N data could only be simulated by accounting for bypass flow, indicating that throughfall water did not fully interact with the soil. Using the calibrated parameter set of the low-N treatment for the high-N treatment resulted in a lower model performance, although time trends were reproduced well also for this treatment. A sensitivity analysis showed model outcome of N transformations to be very sensitive to soil microbial parameters, such as the C efficiency. Use of the 15N tracer data in the calibration lowered uncertainties of these sensitive model parameters. Evaluation of the N input-output budget and microbial N transformations in the ecosystem revealed that lowering N inputs in this N saturated forest soil resulted in a more than proportional decrease of N leaching losses out of the soil system. Gross N transformations decreased under lowered N input, in particular the formation of NO3-N. Net N mineralization was not affected after four years of N manipulations. Net nitrification was decreased to about one third of the rate observed at the high-N deposition plot. Combining 15N tracer data with dynamic simulation modelling provides a powerful tool to improve model performance and process descriptions, and to evaluate impacts of atmospheric N deposition on N cycling in ecosystems.
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