The effect of various nitrogen (N) sources, including riverine dissolved organic matter (DOM), nitrate, ammonium, and urea, on the growth and physiology of the dinoflagellate Prorocentrum minimum was compared in a batch culture experiment. P. minimum grew equally well in the presence of identical amounts of nitrate, ammonium, and urea. Approximately 18 to 20% of organic N bound to the DOM was bioavailable. Although the available N added in the DOM treatment was only 1/3 of the amount of any other N sources, the cell densities of P. minimum in the DOM treatment increased to 61 similar to 65% of those in the nitrate, ammonium or urea treatment. The maximum specific growth rates did not differ significantly between the treatments with the highest in the ammonium treatment (0.55 +/- 0.13 d(-1)) and the lowest in the urea treatment (0.39 +/- 0.04 d(-1)). P. minimum assimilated the available DOM-bound N in a short period (fewer than 5 days), which was faster than utilizing urea. The increase in the cellular N:P ratios of P. minimum showed the alleviation of N stress in all the treatments after the addition of various N forms. The densities and cellular compositions of P. minimum stabilizing in all the treatments for the whole stationary phase indicated that P. minimum has adaptive physiology under sub-optimal conditions and is a competitive bloom species. We suggest that P. minimum cells utilize DOM-bound N for their growth, and the efficiency in utilizing the available DOM-bound N for growth is comparable to when P. minimum utilizes nitrate, ammonium or urea.
- Biologiska vetenskaper