Abstract
Global change is expected to increase cyanobacterial dominance and cyanotoxin production. However, cyanobacterial responses to meteorological events remain uncertain due to limited integrative approaches. Eco-metabolomics offers a promising tool to investigate drivers of phytoplankton successions and metabolite production. We investigated the spatio-temporal dynamics of phytoplankton and their metabolomes in relation to local meteorological conditions in Lake Aydat (France) during summer 2021, sampling both near the Veyre inflow and at the lake center. High-resolution mass spectrometry, combined with phytoplankton biovolumes and physicochemical parameters, revealed two distinct metabolomic fingerprints positively correlated with phytoplankton composition. The first metabolome is composed of mainly lipids and positively correlated with the presence of diatoms throughout the summer until the end of the drought. In contrast, the second metabolome is correlated with the presence of Dolichospermum, that occurrs after a 22-day period without rain and when there is a low nitrate concentration ($NO_3^ - $ ∼ 0.4 mg.l-1). Interestingly, despite similar phytoplankton composition across sites, significant higher abundance of cyanopeptides are detected close to the river inflow during the second rain period, likely driven by higher nutrient inputs and warmer waters compared to the lake center. Overall, these findings demonstrate that fine-scale spatial monitoring can reveal distinct ecometabolomic niches, separated by only 200 m.