An investigation of non-steady-state algal growth. II. Mathematical modelling of co-nutrient-limited algal growth

The ability of mathematical models to simulate competition for nutrients between three algal species, the diatom Thalassiosira pseudonana, a marine raphidophyte Heterosigma carterae and the dinoflagellate Alexandrium minutum, was investigated. Transient growth models were parameterized and tested using a number of closely controlled laboratory data sets including batch monocultures, batch competition experiments and semi-continuous culture competition experiments. The cell quota model of algal growth was found to be adequate to simulate growth of both the raphidophyte and the dinoflagellate. Batch monoculture data for diatom growth obtained under either nitrogen (N) or silicon (Si) limitation could also be simulated with a quota-style model, which in this case included feedback inhibition of nutrient uptake. However, to simulate both batch and semi-continuous culture experiments (and competition between the species), it was necessary to consider diatom Si-N metabolism. A model was derived which contains a representation of both intracellular N ad Si, and of the interaction of these nutrients within the cell. The model used a co-nutrient limitation based on the perceived functional and structural role of N and Si, respectively, within the cell. Simulations indicated that models capable of adequately representing monoculture growth in batch culture may produce erroneous results when incorporated into models of competition. The co-nutrient model is a first step to producing tractable algal growth models which will represent multiple nutrient stress in transient growth conditions.