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. Being at the interface of the vanishing cryosphere, 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 changes in microbial composition 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 ceramic 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, at the in situ water temperature of the stream or at 2ºC warmer than the in situ temperature. This represented eight different flow/temperature conditions, each in triplicate. Biofilms were harvested from the coupons at eleven time points over 6 weeks. Their DNA was extracted and their 16S rRNA genes sequenced to evaluate the community composition of each flow/temperature conditions over time. Preliminary results suggest that the intermittent flow regime is the main driver of microbial community changes, followed by time and temperature, while the other three flows did not change the community composition. 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.