The impacts of climate change on freshwater microbes: Insights from the field to the laboratory

Global climate change, and in particular, global warming is currently one of the greatest threats to freshwater biodiversity. The microbial diversity within freshwaters is phylogenetically and functionally diverse. Yet, the impacts of warming on these complex communities are largely unknown. To date, the vast majority of research ignores the complexity of natural systems, instead, exploring freshwater microbial responses to warming under simplified, undisturbed conditions. I, therefore, assess the impacts of warming on freshwater microbial communities using a range of methodological approaches (field surveys, field experiments and laboratory experiments), while considering other factors which could simultaneously affect freshwater microbial communities, and thus, their responses to warming. To begin, I show that microbial communities from different freshwater microhabitats respond differently to warming. Therefore, to gain a better understanding of the impacts of warming on a given system, microbial communities from multiple microhabitats should be profiled. Next, I studied the impacts of warming on assembling freshwater biofilms across a catchment gradient. I discover that microbial community responses to warming were different in streams located within impacted catchments, compared with microbial communities from unimpacted catchments. Finally, I demonstrate that temperature is a weak environmental filter in the absence of a predator, thus, highlighting the importance of the indirect effects of warming in shaping bacterial communities. I conclude that both the biotic and abiotic variables present in freshwater systems can alter the effects of warming on microbial communities. Therefore, predictions might under- or over-estimate the impacts of warming on freshwater microbial communities if other biotic or abiotic variables present in the system are overlooked