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

摘要

Eight common red tide species including the Dinoflagellates Alexandrium tamarense, Prorocentrum minimum , Prorocentrum mican, Diatoms Skeletonema costatum, Cerataulina pelag-ica, Leptocylindrus minimus, a Raphidophyte Heterosigma akashiwo and a Chrysophyte Isochrysis galbana were chosen to study the effect of four nitrogen substrates (NO_3 ― N, NH_4 ― N, Urea ― N, Mixed ― N) on the growth of these algae. After two transfers, the results showed that at N concentration of 550 μmol, NO_3 ― 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 NO_3 ― N for some species; NH_4 ― N inhibited the growth of all these species except H. akashiwo. At concentrations of 280 and 50 μmol experiments on the growth of I. galbana, P. minimum and L. minimus in NH_4 ― N and NO_3 ― N substrates were also performed. The results showed that the growth rates of I. galbana were not significantly different from each other in NO_3 ― N and NH_4 ― N substrates both concentrations of 280 and 50 μmol. In concentration of 280 μmol NH_4 ― N substrate, the growth rates of P. minimum and L. minimus were slower than in same concentration of NO_3 ― N; At concentration of 50 μmol, the growth rate of P. minimum in NH_4 ― N was not significantly different from that in NO_3 ― N, while the growth rate of L. minimus was only about 30% of that in NO_3 ― 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.