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Intermittent rivers, referring to all temporary, ephemeral, seasonal, and episodic streams, constitute more than half of the global rivers. Even so, not much attention has been given to these ecosystems, until recently, when it was shown that their number are in rise in response to climate change, land-use alteration and water abstraction. Fluctuations between dry and wet conditions within these ecosystems may lead to irreversible modifications of biotic communities and of the ecosystem processes. As a consequence, services provided by the microbial component might be altered influencing whole food web. Within this context we have conducted year-round sampling of microbial mats within the Krčić (Croatia). intermittent stream. Extreme environmental conditions at this site include summer drought, strong rewetting event in the autumn and winter freezing ambient conditions. By targeting 16S rRNA and ITS marker genes we followed response of the microbial community to these strong environmental fluctuations. Results showed high biodiversity within the studied microbial mat harbouring bacteria from 11 different phyla. Cyanobacteria (Microcoleus, Phormidium and uncultured Antarctic cyanobacterium), and Alphaproteobacteria made core of the community, however, fluctuations in the environmental conditions strongly impacted its pattern. In the periods of low temperatures/strong bora wind (winter) and drought (summer), Cyanobacteria were almost completely diminished from the community while populations belonging to the phyla Planctomycetes and candidate phylum TM6, found specifically in this sample, proliferated under this extreme cold. During drought members of the phyla Firmicutes appeared, followed in numbers by Cytophagia‐Fibrella, Polymorphobacter, Polaromonas, and Massilia genera. During autumn, when high water rewetted dry channel desiccant‐tolerant Chroococcidiopsis, Calothrix, and Pleurocapsa cyanobacteria species dominated mat (> 90% of the community), known to possess mechanisms for quick recolonization of environments. In our future studies we will follow potential functional abbreviation within the microbial mat community that might affect their roles in biochemical cycling further impairing whole ecosystem functioning. It is clear that much more attention should be given to investigations on intermittent rivers as being particularly endangered ecosystems, specially due to the lack of adequate management practices and protective policies and legislation. |
