Effects of dissolved organic matter on the growth of Nodularia spumigena (Cyanophyceae) cultivated under N or P deficiency

We investigated the effects of addition of dissolved organic matter (DOM) o n the growth and chemical composition of Nodularia spumigena cells under co nditions of P or N deficiency. Semi-continuous monocultures of N. spumigena Mertens were established. The cells were exposed to the following treatmen ts: nutrient-sufficient (+NP), nitrogen-deficient without DOM (-N) and with DOM (-NDOM), and phosphorus-deficient without DOM (-P) and with DOM (-PDOM ). The -NDOM treatment had the highest N. spumigena cell density (6.1 x 10( 7) cells l(-1)) during the experiment, whereas the P-deficient treatments h ad the lowest cell numbers (0.53 to 0.66 x 10(7) cells l(-1)). Both -P and -PDOM treatments yielded P-deficient N. spumigena cells. Dissolved organic nitrogen may provide N and increase N. spumigena yield under conditions of N deficiency. On the other hand, N. spumigena cells did not use DOM as a P source.