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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Climate change will directly affect carbon and nitrogen mineralization through changes in temperature and soil moisture, but it may also indirectly affect mineralization rates through changes in soil quality. We used an experimental mesocosm system to examine the effects of 6-year manipulations of infrared loading (warming) and water-table level on the potential anaerobic nitrogen and carbon (as carbon dioxide (CO2) and methane (CH4) production) mineralization potentials of bog and fen peat over 11 weeks under uniform anaerobic conditions. To investigate the response of the dominant methanogenic pathways, we also analyzed the stable isotope composition of CH4 produced in the samples. Bog peat from the highest water-table treatment produced more CO2 than bog peat from drier mesocosms. Fen peat from the highest water-table treatment produced the most CH4. Cumulative nitrogen mineralization was lowest in bog peat from the warmest treatment and lowest in the fen peat from the highest water-table treatment. As all samples were incubated under constant conditions, observed differences in mineralization patterns reflect changes in soil quality in response to climate treatments. The largest treatment effects on carbon mineralization as CO2 occurred early in the incubations and were ameliorated over time, suggesting that the climate treatments changed the size and/or quality of a small labile carbon pool. CH4 from the fen peat appeared to be predominately from the acetoclastic pathway, while in the bog peat a strong CH4 oxidation signal was present despite the anaerobic conditions of our incubations. There was no evidence that changes in soil quality have lead to differences in the dominant methanogenic pathways in these systems. Overall, our results suggest that even relatively short-term changes in climate can alter the quality of peat in bogs and fens, which could alter the response of peatland carbon and nitrogen mineralization to future climate change.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science, Ltd
    Global change biology 9 (2003), S. 0 
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Boreal peatlands may be particularly vulnerable to climate change, because temperature regimes that currently constrain biological activity in these regions are predicted to increase substantially within the next century. Changes in peatland plant community composition in response to climate change may alter nutrient availability, energy budgets, trace gas fluxes, and carbon storage. We investigated plant community response to warming and drying in a field mesocosm experiment in northern Minnesota, USA. Large intact soil monoliths removed from a bog and a fen received three infrared warming treatments crossed with three water-table treatments (n = 3) for five years. Foliar cover of each species was estimated annually.In the bog, increases in soil temperature and decreases in water-table elevation increased cover of shrubs by 50% and decreased cover of graminoids by 50%. The response of shrubs to warming was distinctly species-specific, and ranged from increases (for Andromeda glaucophylla) to decreases (for Kalmia polifolia). In the fens, changes in plant cover were driven primarily by changes in water-table elevation, and responses were species- and lifeform-specific: increases in water-table elevation increased cover of graminoids – in particular Carex lasiocarpa and Carex livida– as well as mosses. In contrast, decreases in water-table elevation increased cover of shrubs, in particular A. glaucophylla and Chamaedaphne calyculata. The differential and sometimes opposite response of species and lifeforms to the treatments suggest that the structure and function of both bog and fen plant communities will change – in different directions or at different magnitudes – in response to warming and/or changes in water-table elevation that may accompany regional or global climate change.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 334 (1988), S. 55-58 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] General circulation models suggest a 2-4 °C mean rise in global temperature with CO2 doubling, with greater warming in higher latitudes than near the equator1"5. This doubling is expected to occur over the next one hundred years, although precise estimates of the doubling time vary according to ...
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 361 (1993), S. 208-209 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] How quickly can ecological communities change as the climate warms? Very quickly at the forest-tundra border, say MacDonald et al. in a study of vegeta-tion in Canada over the past 1,000 years, on page 243 of this issue1. With fine-scale resolution of pollen assemblages in ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 431 (2004), S. 639-640 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Sabre-toothed tigers, mastodons, woolly mammoths — these and many other spectacular large mammals are generally thought to have become extinct about 10,000 years ago, at the end of the Pleistocene epoch, otherwise known as the last ice age. But it's becoming clear that some of these species ...
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 317 (1985), S. 613-616 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The present analysis of global soil nitrogen pools is based on data from 3,100 soil profiles supporting natural vegetation (excluding wetlands), therefore the patterns discussed do not account for gains or losses caused by man's activities. The data were obtained from P.J.Z. and from soil survey ...
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 118 (1999), S. 50-58 
    ISSN: 1432-1939
    Keywords: Key words Nutrient use efficiency ; Nutrient response efficiency ; Nutrient availability ; Litterfall ; Production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The validity of nutrient use efficiency as a central concept in ecosystem ecology has recently been subject to challenge based upon arguments over autocorrelation of data, interpretation of graphical approaches, and appropriate statistical analyses. Much of the confusion on the measurement and interpretation of nutrient use efficiency results from the lack of a sound theoretical basis with which to examine experimental results. In this paper, we develop a theory of nutrient use efficiency based upon fundamental mass balance, present a graphical approach to appropriate testing of alternative hypotheses to avoid problems of autocorrelation in data, and suggest critical areas where experiments must be performed to distinguish among hypotheses. We show that nutrient use efficiency (production per unit nutrient uptake) must be distinguished from nutrient response efficiency (production per unit nutrient available). In contrast to the monotonic increase of nutrient use efficiency with decreasing nutrient availability originally proposed in the 1982 model of P.M. Vitousek, nutrient response efficiency is unimodal with maximum efficiency at intermediate levels of nutrient availability. However, nutrient use efficiency dynamics at low nutrient availability cannot yet be theoretically defined. We also show theoretically which plant traits control responses of ecosystem nutrient use or nutrient response efficiency along gradients of nutrient availability. Finally, we show how our model naturally leads to species replacement along nutrient availability gradients.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 96 (1993), S. 186-192 
    ISSN: 1432-1939
    Keywords: N mineralization ; Monocultures ; Soil organic matter ; Grasses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Although Wedin and Tilman (1990) observed large differences in in situ N mineralization among monocultures of five grass species, the mechanisms responsible were unclear. In this study, we found that the species did not change total soil C or N, and soil C: N ratio (range 12.9–14.1) was only slightly, but significantly, changed after four years. Nor did the species significantly affect the total amount of N mineralized (per g soil N) in year-long aerobic laboratory incubations. However, short-term N mineralization rates in the incubations (day 1–day 17) differed significantly among species and were significantly correlated with annual in situ mineralization. When pool sizes and turnover rates of potentially mineralizable N (No) were estimated, the best model treated No as two pools: a labile pool, which differed among species in size (Nl, range 2–3% of total N) and rate constant (h, range 0.04–0.26 wk−1), and a larger recalcitrant pool with a constant mineralization rate across species. The rate constant of the labile pool (h) was highly correlated with annual in situ N mineralization (+0.96). Therefore, plant species need only change the dynamics of a small fraction of soil organic matter, in this case estimated to be less than 3%, to have large effects on overall system N dynamics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two methods of estimating fine root production and turnover are compared for 13 forest ecosystems exhibiting a wide range in form (NH4 + vs. NO3 -) and quantity of available nitrogen. The two methods are by comparison of seasonal maxima and minima in biomess and by nitrogen budgeting. Both methods give similar results for stands with low rates of nitrification. The budgeting method predicts higher fine root turnover and productivity than the max-min method for systems with significant rates of nitrification.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-1009
    Keywords: Recovery ; Disturbance ; Aquatic ecosystems ; Macroinvertebrates ; Fish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract An extensive review of the published literature identified more than 150 case studies in which some aspect of resilience in freshwater systems was reported. Approximately 79% of systems studied were lotic and the remainder lentic. Most of the stressor types were chemical with DDT (N=29) and rotenone (N=15) the most common. The most common nonchemical stressors were logging activity (N=16), flooding (N=8), dredging (N=3), and drought (N=7). The variety of endpoints to which recovery could be measured ranged from sparse data for phytoplankton (N=13), periphyton (N=6), and macrophytes (N=8) to relatively more data for fish (N=412) and macroinvertebrates (N=698). Unfortunately the same characteristics were rarely measured consistently among sites. For example, with respect to fish, more than 30 different species were studied and recovery was measured in many ways, most commonly on the basis of: (1) first reappearance of the species, (2) return time of predisturbance densities, and (3) return time of predisturbance average individual size. Based on these criteria, all systems in these studies seem to be resilient to most disturbances with most recovery times being less than three years. Exceptions included when (1) the disturbance resulted in physical alteration of the existing habitat, (2) residual pollutants remained in the system, or (3) the system was isolated and recolonization was suppressed.
    Type of Medium: Electronic Resource
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