Size-dependent nitrogen uptake in micro- and macroalgae

The role of algal size as a controlling factor for nltrogen uptake kinetics is examined by comparing published values of N uptake rate and half-saturation constants in microand macroalgae. The uptake kinetics differ substantially among algae very different in size. Microalgae take up nitrogen much faster per unit of biomass than macroalgae at both high and low substrate concentrations, and microalgae have significantly higher affinity for nitrogen than macroalgae. These typical differences in the uptake kinetics among small and large algae are commonly attributed to size-specific differences in the relative surface area (SA:V). Regression analysis demonstrates that size-specific variations in the kinetic parameters can be attributed to changes in relative surface area over an extensive range of algal sizes, covering both microand macroalgae. These results agree with previously described relationships between maximum uptake rate of nutrients (nitrogen and phosphorus) and SA:V within narrow size-ranges (either phytoplankton or macroalgae), and emphasize the existence of a general coupling between physiological and morpholog~cal properties in algae.