Fig. 1.

Nitrogen uptake rates of ${\text{NH}}_{\text{4}}^{+}$ (top) and ${\text{NO}}_{\text{3}}^{–}$ (bottom) at the different substrate concentrations. Species names in the key are ordered following the position of the regression line at the end of the N concentration axis to simplify the reading of the figure. However, the order was not necessarily the same as the ranking based on V_max values presented in Fig. 3, which were calculated using all the points and not only the mean values per concentration presented here.