Biogeography shapes high-latitude microbial responses to warming. Arctic streams

Warming is expected to be particularly rapid in the Arctic, but field studies of global warming impacts in aquatic microbial communities have yielded inconsistent results, and experiments suffer from limited realism. We addressed these shortcomings using a continental-scale "natural experiment" in multiple streams around the Arctic Circle, which were warmed naturally by up to 23 deg C and varied in their degree of biogeographic isolation. This provided a first glimpse of what future conditions might look like in these regions where warming is predicted to be especially rapid. We show that temperature had strongly region-specific impacts on taxonomic richness and that the rate of compositional and diversity change increased with isolation, challenging the prevailing view that environmental gradients have an overriding effect on community composition. The results indicate that the impact of warming will not be globally homogenous, so the biogeographic context must be considered when forecasting microbial responses to climate change.