EFFECTS OF NITROGEN AND PHOSPHORUS STRESS ON THE GROWTH OF BOTRYOCOCCUS BRAUNII

The growth of two Botryococcus braunii strains were studied under seven nitrogen and phosphorus stress levels (N: 0-3500 g/L, P: 15-775 g/L) in batch culture at two light intensities of 60 and 110 mol/m2s. Results showed that the tolerance of B. braunii to N and P stress was different between strains, which was further affected by light intensity. B. braunii 764 grew better under N stress, while B. braunii 765 grew better under P stress. The average growth rates of B. braunii 764 with all N stress treatments were significantly higher at the light intensity of 110 mol/m2s than any other treatments. There was no significant difference among the average growth rates of B. braunii 764 and 765 at 60 mol/m2s and B. braunii 765 at 110 mol/m2s treated with N stress. The average growth rates of B. braunii 764 at 110 mol/m2s were significantly lower than other P stress treatments. There was no significant difference among the average growth rate S of B. braunii 764 and 765 at 60 mol/m2s and B. braunii 765 at 110 mol/m2s treated with P stress. Inhibitory effect of N stress on the growth of B. braunii strains was alleviated by the increase of light intensity from 60 to 110 mol/m2s. The growth rates of two B. braunii strains under 3500 g/L N treatment showed no notable difference compared with that under normal Chu-10 medium. The uptake rates of N and P exhibited linear dependence with the initial levels at the 2nd day. N uptake rate reached a saturation point at 3500 g/L N at the 2nd day.