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# Ammonium Uptake by Field-Grown Eriophorum vaginatum Roots under Laboratory and Simulated Field Conditions

G. M. Marion and J. Kummerow
Holarctic Ecology
Vol. 13, No. 1 (Feb., 1990), pp. 50-55
Stable URL: http://www.jstor.org/stable/3682344
Page Count: 6
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## Abstract

Nitrogen (N) deficiencies in tundra ecosystems could be caused, in part, by the kinetics of root N uptake. The objectives of this study were to quantify NH4 uptake by field-grown excised roots of Eriophorum vaginatum I. under controlled NH4 concentrations ($0-250\ \mu {\rm mol}\ {\rm l}^{-1}$) and temperatures (5-20°C) and to evaluate this laboratory derived model as a means of estimating field NH4 uptake. There was no consistent temperature effect on root NH4 uptake which suggests a relative insensitivity of E. vaginatum roots to short-term temperature fluctuations. The Michaelis-Menten equation parameters for NH4 uptake were ${\rm V}_{{\rm max}}=22.1\ \mu {\rm mol}\ {\rm h}^{-1}\ {\rm g}^{-1}$ and ${\rm K}_{{\rm m}}=191\ \mu {\rm mol}\ {\rm l}^{-1}$. Using field NH4 concentrations, field E. vaginatum root biomass data, and the Michaelis-Menten equation, an estimate was made of NH4 uptake over a 42 day period; this estimate of NH4 uptake accounted for 28% of the net incorporation of N into leaves and roots which is a reasonable estimate for E. vaginatum which relies primarily on N retranslocation for supplying new leaves and roots. Major uncertainties in field N uptake rates, model parameterization, and site characterization preclude an accurate model validation and indicate research areas most in need of future study.

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