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30 March 2010 Saturation of NO3 uptake in prairie streams as a function of acute and chronic N exposure
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Abstract

We conducted a series of stepwise NO3 additions to investigate the response of NO3 uptake to short-term (acute) changes in N concentration in 3 prairie streams. Observed NO3 uptake rates increased with short-term elevations in NO3 concentration and were consistent with linear and Michaelis–Menten kinetics models. We compiled these data with uptake rates from additional published studies to calculate robust estimates of N uptake kinetics for prairie streams. Half-saturation coefficients based on compiled data were 6.7 µg/L for NH4 and 67 µg/L for NO3-N. This difference in half-saturation coefficients suggests that NH4 is more efficiently assimilated than NO3, indicating a preference for NH4 as an N source. Similarly, ambient concentrations of NH4 and NO3 were less than their respective half-saturation coefficients, and aerial uptake rates were generally <5% of the maximum, suggesting severe limitation of N uptake at ambient conditions. The observed pattern of uptake kinetics suggests that physiological constraints limit biotic N uptake in these low-N streams and contrasts with the pattern of uptake observed in streams with chronically elevated ambient NO3 concentrations.

Jonathan M. O'Brien and Walter K. Dodds "Saturation of NO3 uptake in prairie streams as a function of acute and chronic N exposure," Journal of the North American Benthological Society 29(2), 627-635, (30 March 2010). https://doi.org/10.1899/09-021.1
Received: 9 February 2009; Accepted: 1 February 2010; Published: 30 March 2010
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