Inter-Research
Aquatic Microbial Ecology

ABSTRACT: We investigated fluctuations in the nitrogen stable isotope ratio (δ¹⁵N) of Chlamydomonas acidophila (Chlorophyceae) by short-interval sampling during a bloom that occurred from 11 May to 29 July 2001 in Lake Katanuma, Japan. In this lake, C. acidophila uses NH₄⁺ as the primary inorganic nitrogenous nutrient, since only trace amounts of other inorganic nitrogenous compounds are present. The δ¹⁵N values obtained for C. acidophila ranged from -7.8 to -3.4‰ during the study period. The lowest values occurred during periods characterized by high concentrations of NH₄⁺ (>15 µmol l^-1), and our results showed that δ¹⁵N values for C. acidophila were negatively correlated with concentrations of NH₄⁺. The results suggest that this nutrient plays a major role in the variation of the δ¹⁵N value for this species. The nitrogen isotope fraction factor (ε) of C. acidophila was much lower than that of many NH₄⁺-based primary producers from other eutrophic environments.

KEY WORDS: Nitrogen · Stable isotope · Phytoplankton · Isotope fractionation · Inorganic nutrient · Acidic lake · Spring bloom · Lake Katanuma

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Published in AME Vol. 36, No. 3 (2004) on September 14
Print ISSN: 0948-3055; Online ISSN: 1616-1564. Copyright © Inter-Research, Oldendorf/Luhe, 2004