Effects of Nitrogen Sources and Concentrations on the Growth of Different Phytoplankton Taxa

Effects of different nitrogen (N) compounds and concentrations on the growth of the three different phytoplankton taxa, Skeletonema costatum (Bacillariophyceae), Prorocentrum micans (Dinophyceae), and Chattonella marina (Raphidophyceae), were investigated. The Monod equation was applied to examine effects of N concentrations on the growth of algal cells. Results showed that nitrate (NO3-N) and urea served as good N sources for the three phytoplankton taxa. S. costatum grew well on all of the seven N sources. C. marina can effectively use the two amino acids, glycine (Gly) and serine (Ser), however cannot utilize alanine (Ala), threonine (Thr), and asparaginic acid (Asp). P. micans cannot grow in five amino acid substrates. All of the three phytoplankton taxa grew well under different proportions of urea-N, and C. marina grew significantly better in medium with both NO3- and urea-N. The values of maximum growth rate (µmax) and half-saturation nutrient concentration (KS) for NO3-N were 0.71 divisions d−1 and 53.55 µmol L−1 for S. costatum, 0.67 divisions d−1 and 23.31 µmol L−1 for P. micans, and 0.23 divisions d−1 and 17.57 µmol L−1 for C. marina, respectively. The results suggested that S. costatum had a high N demand for growth, and was capable of using wide ranges of N compounds. The strategy of N utilization for S. costatum may make this species an advantage in N-enriched sea areas especially the dissolved organic nitrogen (DON) rich coastal waters, which might be the reason why S. costatum widely distributes in the cosmopolitan coastal and estuarine sea areas.