Effects of yttrium and phosphorus on growth and physiological characteristics of Microcystis aeruginosa

Yttrium is a main kind of rare earth elements (REEs) with wide applications in modern industry and farming. Phosphorus, an essential element of algae, is used as the nutrients and also one of the main factors of eutrophication. To investigate the effects of yttrium and phosphorus on Microcystis aeruginosa (M. aeruginosa), the growth and physiological changes were studied by lab cultured experiments. In the experiment, exogenous yttrium was tested by a concentration gradient (0.0, 0.1, 0.3, 0.5, 1.0 mg/L), meanwhile, phosphorus was tested by three concentrations (0.0, 0.02, 0.2 mg/L). The results show that the contents of chlorophyll a (chl-a) and soluble protein increase compared with the control and they have certain correlation with algal cells density. The growth status of algae is stimulated by initial yttrium concentration ≤0.3 and 0.2 mg/L phosphorus, while it is inhabited by 0.5 and 1.0 mg/L yttrium. Besides, the activity of superoxide dismutase (SOD) of algae increases with addition of yttrium dose (0–0.3 mg/L) when phosphorus dose is 0.2 mg/L. Furthermore, when yttrium dose is 0.5 and 1.0 mg/L, the vitality of SOD presents a sharp decline. The malondialdehyde (MDA) contents increase with time and addition of yttrium dose, 0.2 mg/L phosphorus weakens the accumulation of MDA.