Response of alpine stream biofilms to climate change induced stressors

Alpine streams are expected to face an intensification of environmental stressors due to climate change. At the vanishing cryosphere interface, alpine streams are particularly susceptible to increasing temperatures and to changing hydrology. As biofilms are the dominant form of microbial life in alpine streams, monitoring their microbial composition changes due to environmental stressors would inform on how alpine streams respond to climate change. In this study, we designed a flume set-up using water from an alpine stream to directly grow biofilms under hydrological and temperature stressors. Biofilms were grown on clay coupons in flumes under four different flow regimes and two temperatures, as follow: a natural flow reproducing the natural flow events of the alpine stream, a constant flow, a purely stochastic flow, and an intermittent flow with zero-flow days and peak flows, all at the in situ stream temperature or at 2ºC warmer. This represented eight different flow/temperature conditions, each in triplicate. This setup was repeated over to summers, where biofilms were harvested from the coupons for DNA extraction, for bacterial abundance and chlorophyll A quantification, to evaluate the community composition of each flow/temperature conditions over time. Preliminary results suggest that time is the main driver of changes in the microbial community, and is responsible for an increase in bacterial abundance, chlorophyll A concentration and alpha diversity. However, the intermittent flow regime had a significant impact on the microbial composition, while the other flows did not induce changes: drought decreased the bacterial and algal abundance and the alpha diversity, promoted the colonization by members of the Hymenobacter and Massilia genus, while decreased the representation of the Luteolibacter genus. Further analyses will be used to identify the sentinel taxa, ie. taxa driving the phylogenetic turnover in communities, using the “community assembly” and the “phyloscore analysis” frameworks.