Figure 1.

Oxidation of ammonium and formation of nitrite and nitrate in microcosms, which were prepared with Simon, Wuchter, or FG medium, respectively, and labeled nitrogen compounds (left panels). The inoculum consisted of filtered (planktonic) microbes from the FJQ spring. Incubation temperature was 40°C. Substrates (¹⁵NH₄Cl or [¹⁵NH₄]₂SO₄, depending on the medium) were added if less then 10 mg/L NH⁺₄ was measured. Time of addition is indicated by asterisks (✭). Panels on the right show summaries of the formation of nitrite, nitrate, and the decrease of ammonium, respectively, (from top to bottom).