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# Carbon Limitation of Ammonium Uptake by Heterotrophic Bacteria in the Subarctic Pacific

David L. Kirchman, Richard G. Keil and Patricia A. Wheeler
Limnology and Oceanography
Vol. 35, No. 6 (Sep., 1990), pp. 1258-1266
Stable URL: http://www.jstor.org/stable/2837437
Page Count: 9
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## Abstract

The purpose of this study was to test the hypothesis that $NH_4^+$ uptake by heterotrophic bacteria in the subarctic Pacific is C limited. Addition of glucose $(0.5-1.0 \mu M)$ stimulated $NH_4^+$ uptake in unfractionated water but had no effect on bacterial abundance. Glucose stimulation of $NH_4^+$ uptake was even greater in the bacterial size fraction $(<0.8 \mu m)$. Regeneration of $^15 NH_4^+$ from added $[^15 N]$ amino acids was measurable in the bacterial size fraction, but glucose additions prevented net $NH_4^+$ excretion because of increased uptake of $NH_4^+$. In the subarctic Pacific, $NH_4^+$ concentrations range from undetectable $(\leq\le 0.05 \mu M)$ to $0.4 \mu M$, whereas the maximal estimate of monosaccharide concentrations was $0.025 \mu M$. These results indicate that the supply of C compounds like glucose can limit $NH_4^+$ uptake by heterotrophic bacteria.

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