# Drought preceding rain events drives shifts in phytoplankton composition and metabolome in Lake Aydat (France) revealing molecular strategies

## TL;DR

Drought and rain events in Lake Aydat caused changes in phytoplankton types and their chemical profiles, revealing how environmental shifts influence microbial metabolism.

## Contribution

The study introduces a fine-scale spatial and temporal ecometabolomic analysis linking phytoplankton composition to environmental drivers.

## Key findings

- Two distinct metabolomic fingerprints were identified, each correlated with specific phytoplankton groups.
- Cyanopeptides were more abundant near the river inflow during rain events, likely due to higher nutrients and warmer water.
- Spatial differences of just 200 m revealed distinct ecometabolomic niches influenced by drought and rainfall.

## 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 (\documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{upgreek}
\usepackage{mathrsfs}
\setlength{\oddsidemargin}{-69pt}
\begin{document}
$NO_3^ - $\end{document} ∼ 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.

Drought and rainfall induce spatial shifts in phytoplankton metabolism, with site-specific cyanopeptide production reflecting adaptive microbial responses and environmental drivers.