Abstract: To optimize the cultivation conditions of microalgae, singlefactor test was performed to reveal the effects of different nutritional conditions on Phaeodactylum tricornutum mutant strain MP-2, including nitrogen (5, 10, 15, 20, 25, 30, 35 mg·L^-1), phosphorus (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 mg·L^-1), iron sources (FeCl₃, FeC₆H₅O₇, FeSO₄) and their concentrations (0, 0.10, 0.25, 0.50, 1.00 mg·L^-1). The results showed that all these factors exerted significant effects on the growth, total lipid content and fatty acid composition of MP-2 (P<0.05). The highest growth rate was obtained with the nitrogen concentration of 20 mg·L^-1, with the growth rate K values and biomass of 0.384±0.004 and (0.25±0.01) g·L^-1, respectively. The highest total lipid content (26.51±1.96) % was achieved when the nitrogen concentration was 30 mg·L^-1, and the highest PUFA content (37.78±0.35) % occurred when it was 25 mg·L^-1. MP-2 got the fastest growth and highest lipid content when the phosphorus concentration was 2.5 mg·L^-1, and the growth rate K value and biomass were 0.305±0.010 and (0.28±0.02) g·L^-1, respectively. The total lipid content achieved the highest value (21.79±0.89) % when the phosphorus concentration was 1.0 mg·L^-1, and the highest PUFA content occurred when it was 2.5 mg·L^-1. FeSO₄ was proved to be the optimal iron source, and showed significant difference from other iron sources (P<0.05). The optimal FeSO₄ concentration was 0.50 mg·L^-1, with growth rate K value and biomass of （0.495±0.006） and (0.87±0.04) g·L^-1, respectively. The highest total lipid content (28.86±0.50) % was achieved when the FeSO₄ concentration was 0.25 mg·L^-1, and the highest PUFA content occurred when it was 1.0 mg·L^-1. The highest growth rate and total lipid and PUFA contents were obtained with different concentrations of nitrogen, phosphorus and iron, so a cultivation strategy should be adopted in mass culture.

Key words: Karst, sap flow density, Triadica rotundifolia, Radermachera sinica, transpiration water consumption.