In the current experiments, the higher the urea concentration was, the higher the lipid content of the Chlorella sp. Y8-1 when the urea ranged from 0 to 0.25 g/L. The results corresponded with those of several reports; for example, the lipid content of Ellipsoidion sp. increased as the nitrate concentration increased, and the maximal dry weight of 32.8% was obtained when the nitrate-N used was 1.92 mmol/L (Xu et al., 2001). Furthermore, Isochrysis galbana decreased markedly from 30% (NaNO3 > 2 mmol/L) to 19% of dry weight at 0.5 mmol/L NaNO3 (Molina and Sánchez,