Distinct responses from bacterial, archaeal and fungal streambed communities to severe hydrological disturbances

Stream microbes that occur in the Mediterranean Basin have been shown to possess heightened sensitivity to intensified water stress attributed to climate change. Here, we investigate the effects of long-term drought (150 days), storms and rewetting (7 days) on the diversity and composition of archaea, bacteria and fungi inhabiting intermittent streambed sediment (surface and hyporheic) and buried leaves. Hydrological alterations modified the archaeal community composition more than the bacterial community composition, whereas fungi were the least affected. Throughout the experiment, archaeal communities colonizing sediments showed greater phylogenetic distances compared to those of bacteria and fungi, suggesting considerable adaptation to severe hydrological disturbances. The increase in the class abundances, such as those of Thermoplasmata within archaea and of Actinobacteria and Bacilli within bacteria, revealed signs of transitioning to a drought-favoured and soil-like community composition. Strikingly, we found that in comparison to the drying phase, water return (as sporadic storms and rewetting) led to larger shifts in the surface microbial community composition and diversity. In addition, microhabitat characteristics, such as the greater capacity of the hyporheic zone to maintain/conserve moisture, tended to modulate the ability of certain microbes (e.g., bacteria) to cope with severe hydrological disturbances Giulia Gionchetta was awarded a grant (UdG 2016) from the University of Girona. This study was supported by the Spanish Ministry of Economy and Competitiveness through the project FUNSTREAM (CGL2014-58760-C3-R); by the Economy and Knowledge Department of the Catalan Government, through Grant/Award Number: 2014 SGR 484; and through the Short-Term Scientific Mission (STSM) Grant awarded by the Science and Management of Intermittent Rivers and Ephemeral Streams (SMIRES) Cost-Action (Action number: 40271). This study was also partially supported by project BIGLY (ANR-16-CE32-0001) and the project DryHarshSal (RTI2018-097950-B-C21) of the Spanish Ministry of Science, Innovation and Universities