Effects of nitrate on nitrite toxicity to Microcystis aeruginosa

The aim of this study was to investigate the effect of nitrate on nitrite toxicity to Microcystis aeruginosa. Short-term uptake experiment revealed nitrate could depress the nitrite active uptake. The long-term experiment of nitrate effects on nitrite toxicity showed a negative relationship between the growth and intracellular nitrite levels of M. aeruginosa. The net nitrite uptake displayed a decline in the range of 0–150 mg NO 3 - - N L - 1 and an elevation at 200 mg NO 3 - - N L - 1 , whereas the activities of nitrate reductase (NR) were more sensitive to nitrate than nitrite reductase (NiR). As a result, the total intracellular nitrite levels tended to decrease up to 100 mg NO 3 - - N L - 1 then increased at 150–200 mg NO 3 - - N L - 1 . These results suggested the existence of external nitrate could affect the toxicity of nitrite to alga through changing intracellular nitrite content.