Fig. 5. Substrate limitation of nitrification by NH₄–N concentration follows Michaelis–Menten-type kinetics in eight experimental and two standard tanks during the in situ batch experiment (Fig. 2). Each point represents conditions in a single tank over a 2-h period, with measurements repeated every 2 h for 12 h total. Initial NH₄–N concentrations varied from tank to tank due to differences in in situ conditions at start of experiment when flow between tanks was stopped. No significant differences were found between the parameters maximum (non-substrate-limited) nitrification rate (V_max) and half-saturation (Michaelis) constant (K_M) of nonlinear Michaelis–Menten fits to high and low (including standard) plant root treatments (P > 0.10). Line shows the Michaelis–Menten fit to the pooled data set. V_max = 0.811 ± 0.059 mg N L^-1 h^-1, (P < 0.001), K_M = 0.78 ± 0.13 mg N L^-1, (P < 0.001), n = 60, R² = 0.76.