Spatio-temporal disparities in phytoplankton dynamics and metabolite production depending on weather conditions

Various studies suggest that global change is causing an increase in phytoplankton biomass, cyanobacteria prevalence and cyanotoxin production. However, there are conflicting reports regarding the response of cyanobacteria blooms to global warming and meteorological events, probably because of the lack of global approaches. Metabolomics approaches in natural system hold great promise in investigating the factors leading to variations in phytoplankton successions and subsequent cyanotoxin production. However, eco-metabolomics studies are still scares in literature and suffer to adequately unravel the biologically relevant variables under environmental changes. In this study, we investigate the temporal and spatial dynamics of phytoplankton community and the production of their primary and secondary untargeted metabolites in response to local meteorological events. Thus, we collected water samples in two points of the Aydat Lake (France): near the inflowing waters from Veyre River and at the middle of the lake during the 2021 summer. Untargeted intracellular metabolites were measured using ultra-high-performance liquid chromatography coupled with a high-resolution mass spectrometer, as well as phytoplankton biovolume and diversity and physicochemical lake’s parameters. Primarily, our results show the increase of the biovolume of diazotrophic cyanobacteria at the end of the drought and after rain events at both sites. During the drought, we observe a strong increase of intracellular lipid contents, probably in response to sudden nitrogen and phosphorus limitation. Differently, during the wet periods, we observe an increase of the phytoplankton glycerophospholipid content, especially at the middle of the lake, whereas significantly higher abundance of secondary metabolites was monitored at site near the wetland area. Since then, we report a strong correlation between the abundance of different cyanopeptides and the biovolume of Dolichospermum , which is present at both sites, we suggest acclimative responses to cope with the phytoplankton growing stimulation related with the increase of the nutritive ion influx following the rain events. The significant difference in the intra-cellular content in metabolites between the 2 sampling sites, separated by only 200m, while phytoplankton communities were similar suggests the existence of local metabolomic niches.