Utilization of urea by the 6 species of red tide phytoplankton
2007
Fukao, T.(Ehime Univ., Matsuyama (Japan)) | Nishijima, T. | Yamaguchi, H. | Adachi, M.
Utilization of urea by 6 species of red tide phytoplankton was examined to evaluate the contribution of urea to outbreaks of red tides in coastal environments. Skeletonema costatum, Karenia mikimotoi, Prorocentrum minimum and Heterosigma akashiwo could grow on urea effectively as the sole nitrogen source at various urea concentrations, but Chattonella antiqua and Fibrocapsa japonica were unable to grow. The uptake rate of urea for K. mikimotoi and H. akashiwo depended on the urea concentration, and these relationships were expressed by the Michaelis-Menten equation. Uptake kinetic, parameters Vsub(max) and Ks were 2.89 pmol-N cellsup(-1)hsup(-1) and 16.5 microM-N for K. mikimotoi and 1.03 pmol-N cellsup(-1)hsup(-1) and 10.1 microM-N for H. akashiwo, respectively. Uptake rates of urea for both species were usually higher than those for nitrate at the various concentrations that were assumed to approach in situ concentrations. Present results indicate that several species of red tide phytoplankton can rapidly uptake urea and use it for growth even if urea concentration is at in situ levels (less than 10 microM-N). Therefore, the urea availability and the uptake rate of red tide phytoplankton are important characteristics to give an ecological advantages in competition for nitrogen sources among phytoplankton species. We suggest that urea contributes not only to growth of the marine phytoplankton community but to the processes by which a phytoplankton species selectively grows and affects outbreaks of red tides in coastal environments.
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