A DYNAMIC-MODEL OF PHOTOADAPTATION IN PHYTOPLANKTON

We present a new dynamic model that uses a small number of prescribed parameters to predict the chlorophyll a:carbon ratio and growth rate o f phytoplankton in both constant and varying irradiance. The model pro vides a self-contained description of energy and mass fluxes and regul ation of partitioning of photosynthate during phytoplankton adaptation to irradiance. The kinetics and steady-state outcomes of xphotoadapta tion are described in terms of changes in the rates of synthesis of th ree intracellular carbon pools. These pools account for the distributi on of cell material between light-harvesting components, the biosynthe tic apparatus, and energy storage compounds. Regulation of the flow of recent photosynthate to these pools is controlled by the ratio of rea lized to potential photosynthetic electron flow at a given instant. Th e responses of growth rate and Chi a:C to static and dynamic irradianc e regimes can be adequately described by specifying four parameters: t he initial slope of the photosynthesis-irradiance curve, the maximum g rowth rate, the maximum Chi a:C observed under light limitation, and t he maintenance metabolic rate. The model predictions compared favorabl y with observations of the diatoms Thalassiosira pseudonana and Phaeda ctylum tricornutum.