Freshwater bacterioplankton richness in oligotrophic lakes depends on nutrient availability rather than on species-area relationships

We investigated, by means of 454 pyrosequencing, the mechanisms that determine freshwater bacterioplankton richness (a-diversity) in a set of nutrient-poor (oligotrophic) freshwater lakes. To be more precise, the general goal of the present study is to investigate local and regional mechanisms and their respective relevance for driving local bacterioplankton richness (BR) (a-diversity). We hypothesised that BR increases with (i) nutrient availability, (ii) lake area and catchment area, and (iii) lake chain number (a landscape position metric). We found that freshwater bacterioplankton richness was positively influenced by nutrient availability; a result that is consistent with the – in general macro-ecological – finding that the supply of available nutrients is a major driver of species richness. On the contrary, despite the relatively great sampling effort, we did not observe species-area relationships between BR and lake or catchment areas; a finding that re-opens the debate about whether species-area relationships can indeed be found in the microbial world and, thus, are indeed applicable to all organisms from all domains of life.