Trophic gradient is the main determinant of species and large taxonomic groups representation in phytoplankton of standing water bodies

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We used the newly formed database of phytoplankton samples from the Czech Republic, containing 696 taxa from 662 samples of various types of stagnant waters (fishponds, alluvial backwaters, flooded sand- and gravel pits, lakes in abandoned quarries in former coal mines, reservoirs and others) to test for the relationships between phytoplankton composition and productivity, geographical and climatic variables (elevation, temperature, precipitation) and season of the year. As a surrogate of productivity, the number of cells/ml and the total biovolume[μm3]/ml, both spanning over more than six orders of magnitude (from 101 to 107 for the number of cells and from 102 to 109 for the biovolume) were used. The phytoplankton was characterized by its species composition and also by the composition of large taxonomic groups. The data were analysed by constrained ordination (Canonical Correspondence Analysis), including variation partitioning, and by ANOVA of the estimates of species optima based on weighted averages of environmental characteristics.All the explanatory variable groups, i.e. productivity, geography/climate, and season have significant effects on both the species composition and the composition of large taxonomic groups. Productivity is the best predictor of both species and large taxonomic group composition, followed by climatic variables and finally season. The relative effectiveness of productivity as a predictor was considerably greater for large taxonomic groups. The productivity characterized by the number of cells was always a better predictor than when characterized by biovolume. The species optima estimated as weighted averages of corresponding environmental variables show consistent patterns according to large taxonomic groups, but also according to the genera within the groups: in particular, the cyanobacteria and Chrysophyceae preferred on average the most and the least productive environments respectively, however, there were large differences in species preferences also within groups and even within genera. The optima of species on the trophic gradient are suitable characteristics for ecological indication and are presented for more than 400 taxa in the appendix together with estimates of species tolerance.