Plitvice Lakes freshwater network ecosystem
Freshwater network ecosystems consist of connected lotic and lentic environments within same catchment area. On the example of Plitvice Lakes, we investigated changes in environmental conditions and microbial communities (bacteria and fungi) occurring with downstream flow. Water samples from tributaries, interlake streams, interconnections of the cascading lakes, and the Korana River, the main outflow of system, were characterized using amplicon sequencing of bacterial 16S rRNA and fungal ITS2 genes. Our results reveal different environmental conditions, as well as bacterial and fungal communities prevail between the three stream types within the freshwater network ecosystem. Korana River's communities clustered with interlake stream communities', as it is located downstream from interlake streams. The differences of microbial communities were, also, confirmed along the longitudinal gradient between farthest sampling points. Higher a-diversities of microbial communities found in tributaries when reaching lakes undergo through "mass effects" and “species sorting” resulting in less diverse communities. A higher impact of environmental parameters (temperature, O2 and Ca2+ concentrations) was on forming microbial communities in interlake streams, systems with longer WRT, in which the tufa barriers are formed. Higher DOC concentrations due to snow melt impacted communities of tributaries. Despite differences between stream types the microbial community of the Plitvice Lakes is proven to be very stable by the core microbiome, comprising the majority of stream's communities. Our findings indicate a microbial community succession along the river-lake continuum of microbial communities across small freshwater network ecosystem with developed tufa barriers.