ABSTRACT: Nitrogen uptake and assimilation strategies were compared in polar macroalgae from differing dissolved inorganic nitrogen (DIN) regimes. The antarctic endemic, Himantothallus grandifolius, experiences high nitrate concentrations year-round and occasionally high, but variable, ammonium levels. The arctic endemic, Laminaria solidungula, is exposed to seasonal fluctuations in DIN, with N-limitation occurring during the summer. Both species demonstrated saturation kinetics for nitrate and ammonium uptake. L. solidungula showed 'storage-specialist' characteristics of nitrate uptake, with high Vmax allowing this species to take advantage of seasonally elevated nitrate concentrations. H. grandifolius had a high Vmax for ammonium, allowing the alga to utilise pulses of this nutrient. In the presence of both DIN forms, nitrate uptake was significantly reduced in both species. Furthermore, H. grandifolius and L. solidungula demonstrated significantly reduced uptake and assimilation of nitrate during short-term and prolonged periods of darkness, while ammonium uptake and assimilation were relatively unaffected by light. Although preferential uptake of ammonium, particularly in the dark, allows both species to conserve energy in their cold, low-light environments, the antarctic species, which does not have the additional problem of N-limitation, showed stronger energy-conserving traits. Nitrogen assimilation characteristics of the arctic species appeared to balance energy conservation with the need to minimise N-limitation in an environment that alternates between low light and low N-availability.

KEY WORDS: Himantothallus grandifolius · Laminaria solidungula · Nitrogen assimilation · Algae · Antarctic · Arctic

Published in MEPS Vol. 198 (2000) on June 5
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 2000