AME 16:309-314 (1999)  -  doi:10.3354/ame016309

A modified 15N tracer method and new calculation for estimating release of dissolved organic nitrogen by freshwater planktonic algae

Fumitaka Nagao1, Tatsuo Miyazaki2,*

1Laboratory of Marine Environmental Microbiology, Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan
2Marine Ecosystems Research Center, Chiba University, Amatsu-Kominato, Awa-gun, Chiba-ken 299-5502, Japan
*Addressee for correspondence. E-mail:

ABSTRACT: To estimate the release of DON (dissolved organic nitrogen) by freshwater planktonic algae, we modified the Bronk & Glibert method used for marine planktonic algae, by adding NaCl (3.5%) to the freshwater samples and using ion retardation resin columns to separate DON from inorganic nitrogen in the solutions. Clear separation and high recoveries of amino acids indicate that the ion retardation resin column method can be applied to freshwater samples. We derived equations for the calculation of DON release and net DIN (dissolved inorganic nitrogen) assimilation which enable the estimation of the TNR (total nitrogen release) and NNA (net nitrogen assimilation). Further, we derived equations to estimate RANR (recently assimilated nitrogen release; release of DON produced from DIN assimilated during 15N incubation), and PANR (previously assimilated nitrogen release; release of DON produced before the incubation). Using the modified method and equations, we examined time courses of DON release from the cyanobacterium Microcystis novacekii. Both TNR and NNA increased with time during 15N incubation, with more than 91% of the TNR consisting of RANR.

KEY WORDS: Ammonium · Nitrogen uptake · Dissolved organic nitrogen release · Freshwater planktonic algae · Microcystis novacekii · Tracer method

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