Nitrogen-limited growth of marine phytoplankton—I. changes in population characteristics with steady-state growth rate

Abstract

Steady-state growth of Coccochloris stagnina, Cyclotella nana, Monochrysis lutheri and Dunaliella tertiolecta in nitrate limiting medium and of Dunaliella and Monochrysis in ammonium limiting medium is examined in continuous culture experiments. Growth rate can not be directly related to observed nutrient concentration in a chemostat environment except perhaps in a long-term average sense. Nitrate-limited growth rate is related to internal nitrogen per unit population by a hyperbolic expression. These results are consistent with an internal reservoir nutritional mechanism. Steady-state ammonium limited growth takes place without evidence of an internal reservoir, and nitrogen per cell remains constant over all growth rates studied. The relative variability of population carbon, nitrogen, chlorophyll- a, cell volume and cell concentration with steady-state growth rate is examined in the context of using these indicators of the physiological state of the population, rather than environmental parameters, to determine steady-state nutrient-limited growth rate.