Varying Responses to Heat Stress and Salinization Between Benthic and Pelagic Riverine Microbial Communities

Abstract

Microbial communities play a crucial role in the functioning of freshwater ecosystems but are continuously threatened by climate change and anthropogenic activities. Elevated temperatures and salinisation are particularly challenging for freshwater habitats, but little is known about how microbial communities respond to the simultaneous exposure to these stressors. Here, we use mesocosm experiments and amplicon sequencing data to investigate the responses of pelagic and benthic microbial communities to temperature and salinity increases, both individually and in combination. Our results highlight the varying responses of freshwater microbial communities, with sediment communities exhibiting greater stability in response to environmental changes compared to water column communities, and salinisation having a more pronounced impact on microeukaryotes compared to prokaryotes. Simultaneous exposure to elevated temperature and salinity reduced the impact of salinisation on prokaryotes, while microeukaryotes were similarly affected by the combined treatments and salinisation alone. These findings emphasise the complexity of microbial responses to single and multiple stressors, underscoring the need to consider both individual and interactive effects when predicting ecosystem responses to environmental changes.

Keywords: anthropogenic stressors; climate change; freshwater; heatwaves; mesocosm experiment; microbial communities; salinization.

FIGURE 1

Distinct microbial communities in water and sediment samples. Visualisation via principal coordinates analysis (PCoA) based on Bray–Curtis dissimilarity matrices for prokaryotic (left) and microeukaryotic (right) communities. The PCoA plot illustrates the separation between pelagic and benthic microbial communities along axis 1.

FIGURE 2

Varying temporal effect on prokaryotic and microeukaryotic communities in water and sediment samples. Visualisation via PCoA based on Bray–Curtis dissimilarity matrices for prokaryotic (left) and microeukaryotic communities (right) over time with points coloured by time point and facetted by treatment. The PCA plots reveal a strong temporal effect on axis 2 in the pelagic (blue squares) but not in the benthic community (brown circles).

FIGURE 3

Treatment effect on prokaryotic and microeukaryotic communities in water and sediment samples. Visualisation via PCoA plots based on Bray–Curtis dissimilarities calculated from the combined data of all three replicate experiments, showing prokaryotic (left) and microeukaryotic (right) communities in sediment (top) and water (bottom) samples. Each plot displays community changes over time, with treatment groups represented by different colours and shapes, and facetted by replicate to better visualise treatment effects.

FIGURE 4

Alpha‐diversity of microbial communities in water and sediment. Simpson's diversity indices of the prokaryotic (left) and microeukaryotic communities (right) in each treatment throughout the experiments in sediment (brown) and water samples (blue). Days of stressor exposure are highlighted in red.