Notes Effects of four nitrogen substrates on growth of several red tide species

Eight common red tide species including the Dinoflagellates Ale randrium tamarense,Prorocentrum minimum, Prorocentrum mican, Diatoms Skeletonema costatum, Cerataulina pelagica, Leptocylindrus minimus, a Raphidophyte Heterosigma akashiwo and a Chrysophyte Ivohrysis galbana were chosen to study the effect of four nitrogen substrates (NO₃-N, NH₄-N, Urea-N,Mixed-N) on the growth of these algae. After two transfers, the results showed that at N concentration of 550μmol, NO₃-N was the best nitrogen source among these four nitrogen substrates; Urea-N and Mixed-N were also good for the growth of most algae, but not as good as NO₃-N for some species; NH₄-N inhibited the growth of all these species except H. akashiwo. At concentrations of 280 and 50 μmnol experiments on the growth of I. galbana, P. minimum and L. minimus in NH₄-N and NO₃-N substrates were also performed. The results showed that the growth rates of I. galbana were not significantly different from each other in NO₃-N and NH₄-N substrates both concentrations of 280 and 50 μmol. In concentration of 280μmol NH₄-N substrate, the growth rates of P. minimum and L. minimus were slower than in same concentration of NO₃-N; At concentration of 50μmol, the growth rate of P. minimum in NH₄-N was not significantly different from that in NO₃-N, while the growth rate of L. minimus was only about 30% of that in NO₃-N substrate.The results indicated that each alga had its own preference in N-substrate and concentration, therefore,different nitrogen substrates may play a role in red tide formation.