THE EFFECTS OF PHOSPHORUS AND NITROGEN ON THE GROWTH OF CYLINDROSPERMOPSIS RACIBORSKII N8 ISOLATED FROM THE ZHENHAI RESERVOIR

In this study we examined the effects of nitrate and phosphate on the growth of Cylindrospermopsis raciborskii N8 that was isolated from the Zhenhai Reservoir in Guangdong Province. We used a crossed factorial design for three phosphorus levels and three nitrogen levels, and thus generated nine different growth conditions for C. raciborskii. Our results showed that C. raciborskii could adapt to a wide range of phosphorus concentrations (from 0.02 mg/mL to 5.12 mg/mL) and the optimal concentrations for the growth was between 0.16 mg/mL and 5.12 mg/mL. The exponential stage and biomass of C. raciborskii could be significantly enhanced by the increase in the phosphorus level. The kinetic analysis revealed a low KSP value of C. raciborskii N8. This suggested that C. raciborskii N8 could have high affinity for phosphorus and readily become the dominant species in phosphorus-lacking conditions. The results of the nitrogen and phosphorus orthogonal experiments demonstrated that when the nitrogen level was low (0.5 mg/mL), the growth of C. raciborskii N8 was markedly inhibited regardless of the phosphorus level. Moreover, at low phosphorus concentration (0.04 mg/mL) the proliferation of C. raciborskii N8 could be boosted by the increase in nitrogen concentration. It was also found that the growth of C. raciborskii N8 could be significantly improved by HNMP and HNHP treatment. The highlights of our findings were that C. raciborskii in Guangdong reservoirs was highly tolerant to low phosphorus conditions, and nitrogen could be a key factor in its growth.