Abstract
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.
Highlights
Microbes inhabiting intermittent streambeds are responsible for the control and development of many biogeochemical processes essential for fluvial ecosystem functioning
Little is known about the diversity of archaea in inland freshwater ecosystems subjected to water stress conditions
The taxonomic composition of the initial bacterial, archaeal and fungal communities showed no significant differences between treatments (Table S1, Fig. S1)
Summary
Microbes inhabiting intermittent streambeds are responsible for the control and development of many biogeochemical processes essential for fluvial ecosystem functioning. Current global models predict temperature increases in the Mediterranean Basin, coupled with strengthened periods of drought and intense sparse flash storm episodes[4,5] In this context, water scarcity is usual in Mediterranean freshwater ecosystems that experience the typical climate combination of high summer temperatures and extreme seasonal variation in rainfall patterns[6]. Recent research has highlighted the observed capacity of microbes to develop resistance and drought legacy in the case of repeated perturbations[12,13,14] These contrasting observed responses could be due to intrinsic differences in the microbial life strategies of bacteria, archaea and fungi, and/or in the occupied streambed microhabitat (such as surface and hyporheic zone sediments or decomposing plant material accumulation). The variety of micro-habitats and storm episodes would further differentiate the microbial response trajectories, already recognized as multifaceted, between dry and wet phases
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