Coupling Nutrient Uptake and Energy Flow in Headwater Streams |
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Authors: | C S Fellows H M Valett C N Dahm P J Mulholland S A Thomas |
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Institution: | (1) Centre for Riverine Landscapes, Faculty of Environmental Sciences, Griffith University, Nathan, Queensland, 4111, Australia;(2) Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA;(3) Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA;(4) Environmental Sciences Division, Oak Ridge National Laboratories, Oak Ridge, Tennessee 37831-6036, USA;(5) Department of Ecology and Evolutionary Biology, Cornell University, Corson Hall, Ithaca, New York 14853-2701, USA |
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Abstract: | Nutrient cycling and energy flow in ecosystems are tightly linked through the metabolic processes of organisms. Greater uptake
of inorganic nutrients is expected to be associated with higher rates of metabolism gross primary production (GPP) and respiration
(R)], due to assimilatory demand of both autotrophs and heterotrophs. However, relationships between uptake and metabolism
should vary with the relative contribution of autochthonous and allochthonous sources of organic matter. To investigate the
relationship between metabolism and nutrient uptake, we used whole-stream and benthic chamber methods to measure rates of
nitrate–nitrogen (NO3–N) uptake and metabolism in four headwater streams chosen to span a range of light availability and therefore differing rates
of GPP and contributions of autochthonous carbon. We coupled whole-stream metabolism with measures of NO3–N uptake conducted repeatedly over the same stream reach during both day and night, as well as incubating benthic sediments
under both light and dark conditions. NO3–N uptake was generally greater in daylight compared to dark conditions, and although day-night differences in whole-stream
uptake were not significant, light–dark differences in benthic chambers were significant at three of the four sites. Estimates
of N demand indicated that assimilation by photoautotrophs could account for the majority of NO3–N uptake at the two sites with relatively open canopies. Contrary to expectations, photoautotrophs contributed substantially
to NO3–N uptake even at the two closed-canopy sites, which had low values of GPP/R and relied heavily on allochthonous carbon to
fuel R. |
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Keywords: | metabolism nitrogen carbon primary production respiration autotroph heterotroph autochthonous allochthonous |
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