Abstract: To explore the responses of Microcystula aeruginosa to UV radiation, the toxic and non-toxic strains of M. aeruginosa were treated with visible light PAR (400-700 nm) and full-wavelength PAR+UVR (295-700 nm), under the radiation intensity of PAR=40.8 W·m^-2 and UVR=5.0 W·m^-2. Both toxic and non-toxic strains were exposed to radiation for 2 h (12:00-14:00) per day and lasted for seven days. The results showed that the maximum photochemical efficiency (F_v/F_m) of both strains were inhibited in the early stage of UV radiation exposure and gradually recovered in the later stage. The relative contents of phycobiliprotein (APC/Chl-a and PC/Chl-a) and carotenoids (Car/Chl-a) under PAR+UVR radiation were higher than those under PAR condition, and showed an increasing trend with the duration of radiation. The increase of photosynthetic pigment content in the toxic strain was significantly lower than that in the non-toxic strain, while the activity of antioxidant enzymes was rapidly induced and higher than that in the toxic strain. Under UV radiation, extracellular polysaccharide (EPS) and microcystin contents in the toxic strain significantly increased. Under PAR and PAR+UVR radiation treatments, the toxic strain had higher growth rate and stronger adaptability than the non-toxic strain.

Key words: Microcystis aeruginosa, UV radiation, photosystem II, antioxidant enzyme, photosynthetic pigment