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 chl orophyll a:carbon ratio (theta), is a universal feature of all phytopl ankton studied to date. We derive a dynamic regulatory model that pred icts the dependencies of theta and growth rate (mu) on irradiance, day length, temperature and nutrient availability. The model requires spec ification of 4 parameters to describe the Light-dependencies of theta and mu under nutrient-saturating conditions at constant temperature. T hese are the maximum value of theta (theta(m)), the initial slope of t he chl a-specific photosynthesis-light response curve (alpha(chl)), th e maximum carbon-specific photosynthesis rate (P-m(C)) and the cost of biosynthesis (zeta). The influences of temperature and nutrient avail ability are accommodated through their effects on P-m(C). The temperat ure 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 empirica l studies suggests that microalgal cells adjust theta in response to a n imbalance between the rate of Light absorption and the energy demand s for photosynthesis and biosynthesis.