Rates of NH 4 + uptake, intracellular transformation and dissolved organic nitrogen release in two clones of marine Synechococcus spp.

Author： Bronk DA

Publisher： Oxford University Press

ISSN： 1464-3774

Source： Journal of Plankton Research, Vol.21, Iss.7, 1999-07, pp. : 1337-1353

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Abstract

Evidence suggests that phytoplankton can release significant amounts of dissolved organic carbon (DOC), particularly when they are nitrogen (N) deficient. To investigate this phenomenon from the perspective of dissolved organic N (DON), ¹⁵N tracer techniques were used to trace the flow of N through two clones of Synechococcus, WH7803 and WH8018, which were grown in batch culture under N-sufficient and N-deficient conditions. At various stages during the experiment, a subsample of the culture was removed and the response to a pulse of ¹⁵N-labeled NH4⁺ was measured with respect to rates of NH4⁺ uptake, intracellular NH4⁺ transformation, and release of total and low-molecular-weight (LMW; <10 000="" da)="" don.="" in="" contrast="" to="" what="" is="" commonly="" observed="" for="" doc,="" high="" rates="" of="" don="" release="" were="" not="" observed="" during="" n="" starvation="" in="" either="" clone.="" the="" highest="" rates="" of="" don="" release,="" both="" absolute="" and="" as="" a="" percentage="" of="" gross="" n="" uptake,="" occurred="" during="" n-sufficient="" growth,="" and="" release="" rates="" decreased="" by="" a="" factor="" of="" 4-7="" when="">4⁺ was depleted in the medium.