Dynamics of nitrogen-fixing cyanobacteria with heterocysts: a stoichiometric model

A simulation model for nitrogen-fixing cyanobacteria was formulated to predict population and nutrient dynamics in water quality studies. The model tracks population biomasses of nitrogen and phosphorus, which potentially limit population growth. Lack of intracellular nitrogen cues the differentiation of specialised heterocysts for nitrogen fixation. Ecoevolutionary analysis presented here predicts that natural selection optimises heterocyst differentiation in relation to external supplies of nitrogen and phosphorus. Modelling the production of N-rich toxins (e.g. anatoxins, saxitoxins) suggests that both total biomass and the biomass N : P ratio can predict concentrations of toxins. The results suggest hypotheses that major taxa of nitrogen-fixing, nuisance cyanobacteria are differentially adapted to varying nitrogen and phosphorus supplies, and that biomass stoichiometry is related to toxins production in this major group of harmful algae. This approach can be extended into models of community and ecosystem dynamics to explore implications of nitrogen fixation for cyanobacterial biomass and toxins production.