The elemental composition of primary producers reflects the availability of light, carbon and nutrients in their environment. According to the carbon-nutrient balance hypothesis, this has implications for the production of secondary metabolites. To test this hypothesis, we investigated a family of toxins, known as microcystins, produced by harmful cyanobacteria. The strain Microcystis aeruginosa HUB 5-2-4, which produces several microcystin variants of different N:C stoichiometry, was cultured in chemostats supplied with various combinations of nitrate and CO2. Excess supply of both nitrogen and carbon yielded high cellular N:C ratios accompanied by high cellular contents of total microcystin and the nitrogen-rich variant microcystin-RR. Comparable patterns were found in Microcystis-dominated lakes, where the relative microcystin-RR content increased with the seston N:C ratio. In total, our results are largely consistent with the carbon-nutrient balance hypothesis, and warn that a combination of rising CO2 and nitrogen enrichment will affect the microcystin composition of harmful cyanobacteria.
Van de Waal, D. B., Verspagen, J. M. H., Lürling, M., Van Donk, E., Visser, P. M., & Huisman, J. (2009). The ecological stoichiometry of toxins produced by harmful cyanobacteria: an experimental test of the carbon-nutrient balance hypothesis. Ecology Letters, 12(12), 1326-1335. https://doi.org/10.1111/j.1461-0248.2009.01383.x