Dynamic model of phytoplankton growth and acclimation: Responses of the balanced growth rate and the chlorophyll a:carbon ratio to light, nutrient-limitation and temperature

Acclimation of the photosynthetic apparatus to changes of irradiance, temperature and nutrient availability, involving regulation of the chlorophyll a:carbon ratio (theta), is a universal feature of all phytoplankton studied to date. We derive a dynamic regulatory model that predicts the dependencies of theta and growth rate (mu) on irradiance, daylength, temperature and nutrient availability. The model requires specification of 4 parameters to describe the Light-dependencies of theta and mu under nutrient-saturating conditions at constant temperature. These are the maximum value of theta (theta(m)), the initial slope of the chl a-specific photosynthesis-light response curve (alpha(chl)), the maximum carbon-specific photosynthesis rate (P-m(C)) and the cost of biosynthesis (zeta). The influences of temperature and nutrient availability are accommodated through their effects on P-m(C). The temperature dependence is described by the slope of an Arrhenius plot and the nutrient dependence is described through the half saturation constant (K-N) of the Monod equation. Fidelity of the model results to empirical studies suggests that microalgal cells adjust theta in response to an imbalance between the rate of Light absorption and the energy demands for photosynthesis and biosynthesis.