MODELING CARBON CELL QUOTA IN LIGHT-LIMITED PHYTOPLANKTON

The carbon cell quota of light-limited microalgae often increases with average photon flux density. Models of light-limited microalgal growt h do not account for this phenomenon, however. In this paper we presen t a model of the carbon budget of phytoplankton, which accounts for th e variation in carbon cell quota with photon flux density. We distingu ish two components in the cell, permanent biovolume and a transient ca rbon pool. Furthermore, we distinguish three processes: assimilation, maintenance and growth. Assimilation acts to increase the transient ca rbon pool, whereas maintenance and growth both act to decrease it. Mai ntenance represents a sink of carbon; in contrast, growth leads to an increase of permanent biovolume. We derive equations describing the ca rbon cell quota, the specific growth rate, photosynthesis and dark res piration. The model accurately describes data on the complete carbon b udget of three widely different phytoplankton species. We show that th e model is a generalization of the well-known Droop model for nutrient limited growth. This result indicates that light and nutrient limited growth may be less dissimilar than is generally thought. (C) 1997 Aca demic Press Limited.