Phytoplankton functional response to spatial and temporal differences in a cold and oligotrophic lake

We explored phytoplankton communities from a functional perspective in two connected but hydro-morphologically distinct basins during the ice-free period in the cold and oligotrophic Lake Tovel, Italy. Despite the absence of dispersal barriers, we expected a clear separation of the phytoplankton communities between basins based on their physical distinctions: a shallow and a deep basin with low and high water residence time, respectively. To investigate seasonal succession and spatiality, taxa were classified according to their functional groups (FGs) and traits (FTs). Relationships between functional classifications and environmental parameters were assessed by non-metric multidimensional scaling integrated with cluster analysis. Clustering of FGs and FTs was complementary and reflected different hydrological conditions of each basin: (i) more stable conditions and higher functional variation across seasons in the deep basin and (ii) less stable conditions and lower functional variation across seasons in the shallow basin. Phytoplankton functional composition evidenced how local conditions selected for corresponding functional attributes adapted to each basin’s environment. These results, together with the presence of rare, cold-tolerant taxa such as Pseudotetraëdriella kamillae and Stephanocostis chantaicus, highlighted the need for long-term phytoplankton studies, and the creation of a FG that includes cold-adapted, oligotrophic taxa