Nitrogen sources for the growth of marine microalgae: role of dissolved free amino acids

Abstract

Dissolved free amino acids (DFAA) form a significant proportion of dissolved fixed nitrogen in marine waters and could provide an additional source of nitrogen for the growth of marine microalgae.With the advent of DFAA analysis by HPLC, recent studies of algal physiology, and an increased awareness of potential experimental errors, doubts are cast over the conclusion that marine microalgae are not net users of DFAA.Results obtained by testing the use of a few amino acids cannot be extrapolated; the full range of amino acids should be used in field experiments.A high rate of uptake of any one amino acid is not to be expected.It is more probable that a simultaneous uptake of several amino acids will occur at a lower rate.It is essential that environmental conditions be taken into account in interpretation of results from field experiments.Results from laboratory and field studies suggest that maximum rates of DFAA uptake would occur in dark conditions in waters depleted of dissolved inorganic nitrogen.Turbid estuaries and coastal waters would also be environments likely to induce a significant uptake of amino acids, because levels of nFA.4 i.n.sl~ch WB!P~S S ~C :~!st;l.~.~!y high and the periods of enforced darkness due to turbidity are likely to induce the development of microalgal amino acid uptake systems.