title: ALKALINE PHOSPHATASE ACTIVITY AS A FUNCTION OF INTERNAL PHOSPHORUS CONCENTRATION IN FRESHWATER PHYTOPLANKTON(1).
abstract: Single-cell alkaline phosphatase (AP) activity is being increasingly used to characterize phosphorus (P) status of individual species of phytoplankton. As phytoplankton growth rates depend more directly on the internal rather than external P concentrations, we determine the AP activity in the two species of freshwater phytoplankton, Scenedesmus quadricauda (Turpin) Bréb. and Asterionella formosa Hassall, as a function of internal P concentration. AP activity strongly correlated with cellular P, increasing almost linearly with decreasing cellular P in both species. The dynamics of initial responses of AP activity to P limitation, as well as the final levels of AP activity, when cellular P approached minimum quotas, differed in two species. After P addition, cellular P concentrations increased rapidly, but AP activity remained high for several days. The lag in AP activity down-regulation following an increase in cellular P made it difficult to infer current P status of cells under dynamic P conditions.
authors.affiliation: Michigan State University, Kellogg Biological Station, Hickory Corners, Michigan 49060, USAGeorgia Institute of Technology, Atlanta, Georgia 30332, USA.
authors.forename: Elena
authors.initials: E
authors.lastname: Litchman
authors.affiliation: Michigan State University, Kellogg Biological Station, Hickory Corners, Michigan 49060, USAGeorgia Institute of Technology, Atlanta, Georgia 30332, USA.
authors.forename: Binh L V
authors.initials: BL
authors.lastname: Nguyen
keywords: alkaline phosphatase; cellular P quota; chlorophyll; diatoms; green algae; phosphorus limitation; phytoplankton