Diazotrophy modulates cyanobacteria stoichiometry through functional traits that determine bloom magnitude and toxin production

Harmful cyanobacterial blooms are an increasing threat to water quality. The interactions between two eco-physiological functional traits of cyanobacteria, diazotrophy (nitrogen (N)-fixation) and N-rich cyanotoxin synthesis, have never been examined in a stoichiometric explicit manner. We explored how a gradient of resource N:phosphorus (P) affects the biomass, N, P stoichiometry, light-harvesting pigments, and cylindrospermopsin production in a N-fixing cyanobacterium, Aphanizomenon. Low N:P Aphanizomenon cultures produced the same biomass as populations grown in high N:P cultures. The biomass accumulation determined by carbon, indicated low N:P Aphanizomenon cultures did not have a N-fixation growth tradeoff, in contrast to some other diazotrophs that maintain stoichiometric N homeostasis at the expense of growth. However, N-fixing Aphanizomenon populations produced less particulate cylindrospermopsin and had undetectable dissolved cylindrospermopsin compared to non-N-fixing populatio...