Résumé
Abstract While climate change affects the phytoplankton biodiversity at both local and global scales, predicting phytoplankton community responses to warming is impaired by their polyphyletic complexity. High mountain lakes are highly vulnerable systems, partly due to their limited biodiversity, and forecasting their ecological trajectories is a key challenge for scientists and conservation managers. We evaluated the phytoplankton's sensitivity to temperature in 24 high‐altitude lakes over a multi‐year (average 7‐year) study. We detected assemblage‐specific responses to warming, with different trends in biovolume and diversity observed among the diatom‐dominant, mixed‐mixotrophs dominant, and colonial‐green dominant assemblages. The environmental settings partly governed assemblage responses, highlighting the role of the landscape filters in determining the response to warming. The biological stability of lakes, that is, their ability to resist shifts in their phytoplankton assemblage, is therefore determined both by the lake characteristics and warming intensity.