Consideration in vitro of photosynthetically active radiation as a relevant parameter associated with cyanobacteria in a tropical monomictic aquatic system

Abstract Studies performed in Valle de Bravo (VB) reservoir in Mexico record the presence of cyanobacteria proliferation and microcystin LR (MC-LR), both from 1998 to 2022, related mainly to two environmental factors; first, nitrates (NO3) and second, temperature. We statistically analyzed data from nine selected works in VB and found that these parameters do not converge seasonally during stratification and mixing. We propose that cyanobacteria, being photoautotrophic organisms, their proliferation and toxin-producing capacity are mainly determined by the amount of photosynthetically active radiation (PAR) rather than NO3. We conducted experimental tests to evaluate the toxic wild cyanobacterium, Microcystis aeruginosa, producer of microcystin LR (MC-LR), exposed to 100 µmol photons m−2 s−1 of PAR and three fractions at different descending concentrations of NO3. The results of the analyses on data from nine studies showed that cyanobacteria did not proliferate due to the seasonal availability of NO3 but rather due to temperature. In vitro, we observed that increased PAR had an effect on the growth of M. aeruginosa. The presence of MC-LR was driven by the inverse relationship between PAR and NO3. Therefore, we conclude that adding PAR monitoring to studies of tropical monomictic systems would contribute to expanding our understanding of NO3 and temperature-related effects on the proliferation of cyanobacteria and their toxins.