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    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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  • 2
    ISSN: 1573-515X
    Keywords: carbon dioxide ; hysteresis ; methane ; peat ; temperature ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The ability to predict the effects of climate change on trace gas fluxes requires a knowledge of microbial temperature responses. However, the response of a microbial community to temperature in a given substrate may be complicated by its thermal history. To examine the effect of sequentially changing temperature on methane and carbon dioxide production in different peat types, we incubated anaerobic peat samples from 3 types of northern peatlands, a bog, a sedge fen and a cedar swamp, in both rising and falling temperature regimes. Graphic and statistical comparisons of the different temperature regimes suggest hysteresis in microbial response to temperature, although the absolute rates at any given temperature often did not differ. Where regressions for temperature response (Arrhenius plots) were significant, they generally differed between temperature regimes. The greatest differences among treatments occurred during the first half of the 40-d incubation. Increases in carbon dioxide production were similar across all peat types, but methanogenesis varied widely: methane production was uniformly low in the bog peat but increased sharply with temperature in the other two peat types. The complicating effect of history or chronology on substrate responses to environmental stimuli may restrain our ability to model the responses of complex systems to changing conditions.
    Type of Medium: Electronic Resource
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