黑暗条件下不同氮源对铜绿微囊藻(Microcystis aeruginosa)生长和pH的影响

在黑暗条件下,利用不同形态的氮源(硝酸盐氮,氨氮,有机氮和硝酸盐氮,有机氮)培养蓝藻水华优势种铜绿微囊藻(Microcystis aeruginosa),分析其氮代谢和对水体pH的影响.研究结果表明,在不同氮源的培养液中铜绿微囊藻密度在最初的24 h内出现波动,之后下降.培养液中pH值在试验最初的24 h显著下降,之后趋于稳定,在硝态氮培养液中pH值下降最大,从8.18下降到7.19,其反硝化作用产生的NO-2浓度也最大.不同氮源培养液中总氮含量都有所下降,以混合氮源培养液中总氮减少量最大,说明化合态氮经过反硝化作用生成了氮气并溢出培养液,因此,在黑夜条件下藻华水体中存在反硝化作用.

Effect of different nitrogen forms on the growth of Microcystis aeruginosa and pH in the medium under darkness

To investigate the nitrogen metabolism by M. aeruginosa and pH changes in the mediums under darkness, we cultured Microcystis aeruginosa, a dominant species in algal bloom, with different nitrogen forms including NO-3, NH+4, Bicine (N, N-Bis(2-hydroxyethyl) glycine) and Bicine + NO-3. Our results show that the densities of M. aeruginosa fluctuate within first 24 h of culture, and decrease after 24 h. However, the pH values in the mediums decrease significantly within the first 24 h in all experimental treatments and then gradually stabilize to a fixed value. The biggest decrease of pH value appears in the NO-3 medium, changing from 8.18 to 7.19. Interestingly, the biggest increase of NO-2 concentration appears in the same medium. The total amount of nitrogen decreases in all experimental mediums, specially in the medium containing Bicine and NO-3, and the decreased nitrogen is transformed to N2 through denitrification, then escaping from water into air. The results suggest that denitrification of M. aeruginosa happens when nitrate is supplied under darkness.