Effects of Nitrogen and Phosphorus on the Growth of Levanderina fissa:How It Blooms in Pearl River Estuary

摘要

Effects of nitrogen(N) and phosphorus(P) from different sources and at different concentrations on the growth of Levanderina fissa(= Gyrodinium instriatum) were studied in laboratory conditions. The findings might explain the recurrent blooms of this species in Pearl River Estuary, China. Results showed that nutrient limitation significantly inhibited the growth of L. fissa. The values of specific growth rate(μmax) and half-saturation nutrient concentration(KS) were 0.37 divisions/d and 8.49 μmol L^(-1) for N, and 0.39 divisions/d and 1.99 μmol L^(-1) for P, respectively. Based on KS values, dissolved inorganic N level in PRE was sufficient to support the high proliferation of L. fissa, while dissolved inorganic P concentration was far lower than the minimum requirement for its effective growth. L. fissa was not able to utilize dissolved organic N(DON) compounds such as urea, amino acids, and uric acid. However, it grew well by using a wide variety of dissolved organic P(DOP) sources like nucleotides, glycerophosphate, and 4-nitrophenylphosphate. The results from this study suggested that the ability in DOP utilization of L. fissa offers this species a competitive advantage in phytoplankton communities. The high level and continuous supply of DIN, enrichment of DOP, together with warm climate and low salinity in the Pearl River Estuary provided a suitable nutrient niche for the growth of L. fissa, and resulted in the recurrent blooms in the estuary.