Kinetics of nitrate uptake by freshwater algae

The kinetics of nitrate (NO₃ ^–) uptake, the maximum uptake velocity (V_m) and the half-saturation constant (K_s), were determined for 18 species of batch-cultured freshwater algae grown without nitrogen limitation. Values of K_s ranged from 0.25 to 6.94 µM l^–1 Chlorella pyrenoidosa Chick, and Navicula pelliculosa (Breb.) Hilse, respectively. Values of V_m ranged from 0.51 to 5.07 µM l^–1 h^–1 for Anabaena A7214 and Nitzschia W-32 O'Kelley, respectively. The mean positive values of K_s for Chlorophyta, Cyanophyta and Chrysophyta were 1.89, 3.67 and 4.07 µM l^–1, respectively. The mean values of V_m for the same phyla were 1.61, 1.02 and 2.97 µM l^–1 h^–1 10⁵ cells^–1, respectively. The ranges of these kinetic parameters encompass values of kinetic parameters for marine and freshwater species in batch culture, for freshwater algae grown in N-limited chemostats and for natural populations of freshwater phytoplankton. Thus, in spite of variability between species, uptake parameters for both marine and freshwater algae are identical.