Fig. 4.

Variation partitioning analysis of 16S rRNA gene data sets from Lake Bourget (A and B) and Lake Annecy (C and D) at 2 m (A) versus 50 m (B) and at 3 m (C) versus 45 m (D), respectively. Pure bottom-up variables were nitrate, ammonium, total phosphorus, and silicates. In Lake Bourget, physicochemical parameters were temperature, nitrate, ammonium, and total phosphorus for 2-m samples and nitrate, ammonium, total phosphorus, silicate, dissolved oxygen, and chlorophyll a for 50-m samples. Apparent top-down variables were ciliate and HNF abundances at 50 m. In Lake Annecy, physicochemical factors were nitrate, total phosphorus, silicates, dissolved oxygen, and chlorophyll a for 3-m samples and temperature, silicate, nitrate, ammonium, total phosphorus, dissolved oxygen, and chlorophyll a for 45-m samples. Pure bottom-up factors were PNF and viruses at 3 m and HNF and viruses at 45 m. For each data set, P < 0.01.