LAUSR

Organic nitrogen and inorganic nitrogen were the main nitrogen sources in the north and south of Dianchi Lake, respectively. Thus, the effect of the different concentration (0.5, 1.0, 2.0, 5.0, 10, 20, 50 mg/L) of ammonium nitrogen (NH4-N) and alanine on growth of Microcystis aeruginosa and Scenedesmus quadricauda was investigated. In NH4Cl vitro co-culture, M. aeruginosa grew better than S. quadricauda, and its chlorophyll a increased to 2893.94 ug/L in 2 mg/L NH4Cl group. In vitro alanine treatments, S. quadricauda’s chlorophyll a was measured at 5034.34 ug/L in 50 mg/L alanine, which was higher than M. aeruginosa. M. aeruginosa in NH4Cl vitro monocultures showed better cell structure in 20 mg/L NH4Cl, and its chlorophyll a was higher than that of the corresponding concentration of alanine. The photosynthetic activity (Fv/Fm), the maximum electron transfers rate (ETRmax), and the saturated light intensity point (Ik) of M. aeruginosa increased with the ammonium concentration, and decrease with the alanine concentration, indicating that M. aeruginosa can tolerate higher concentrations of ammonium chloride. In high concentrations of NH4Cl, S. quadricauda’s cell was seriously damaged, but of alanine alone, it was intact. Fv/Fm, ETRmax, and Ik of S. quadricauda increased with the alanine concentrations, showing that S. quadricauda makes better use of organic nitrogen.