Effects of nitrogen supply and its composition on the growth of Prorocentrum donghaiense

► Growth of Prorocentrum donghaiense on various forms of N compounds and growth on combinations of dissolved N compounds presented at different ratios were reported. ► P. donghaiense grew best on ammonium, nitrate and urea but could also grow with glutamic acid, the dipeptide phenylalanine-alanine or cyanate as sole sources of N. ► Different N ratios affected the growth of P. donghaiense. ► Nitrate uptake was inhibited by ammonium, glutamic acid and urea, but ammonium uptake was not inhibited and appeared to be stimulated by urea and glutamic acid. In order to better understand the complex nitrogen (N) dynamics contributing to blooms of the harmful alga, Prorocentrum donghaiense, in eutrophic environments, we compared the growth of this organism on various forms of dissolved inorganic (nitrate and ammonium) and organic N (urea, glutamic acid, peptides and cyanate) compounds both individually and in combination. Growth rates of P. donghaiense were comparable in cultures grown with ammonium, nitrate, urea, glutamic acid, or the dipeptide phenylalanine-alanine as the sole source of N. P. donghaiense could also grow with cyanate or dialanine as sole sources of N, but at lower rates. Different DON urea, glutamic acid or diala:DIN nitrate or ammonium ratios and nitrate:ammonium ratios also affected the growth of P. donghaiense. Growth rates of cultures acclimated on media with combinations of nitrate or ammonium and DON (urea, glutamic acid or alanine-alanine), grew faster than those growing on DON alone. The ratio of nitrate:ammonium in the growth media had little effect on the growth of P. donghaiense. Our uptake experiments exhibited complicated interactions among different nutrients. Nitrate uptake was inhibited by ammonium, glutamic acid and urea. In contrast, ammonium uptake was stimulated by urea and glutamic acid. Further research is needed to understand how the complex mixture of N compounds found in natural systems contributes to the growth and proliferation of P. donghaiense in the environment as this has implications for nutrient management. Because nitrate concentrations are elevated in areas prone to P. donghaiense blooms, nutrient reductions have targeted nitrate. The results presented here suggest that total N loads must be reduced to prevent blooms of this organism in coastal waters.