Abstract: Employing capillary-pipette washing method,the unialgal strain and axenic strain of Microcystis aeruginosa from Songhua Lake were isolated and purified,and effects of temperature,illuminance,nitrogen,phosphorus,and iron on their growth were investigated.The results showed that there was no significant difference under the influences of temperature,illuminance,nitrogen,phosphorus,and iron on the maximum specific growth rate of the unialgal strain and axenic strain.It reaches the maxirnum specific growth rate under the conditions of 33 ℃ of temperature,5 000 Lx (2 000 Lx) of illuminance,1.2 mg·L^-1 of NO₃^--N,0.06 mg·L^-1 of PO₄^3--P and 0.05 mg·L^-1 (0.04 mg·L^-1) of ferric citrate.With the increase of N,P and Fe concentrations,maximum growth of the unialgal strain was much higher than that of the axenic strain.Thus,it would be able to improve the growth of M.aeruginosa if the associated bacteria presented.In view of N,P and Fe concentrations and the conditions of temperature and illumination in Songhua Lake,there exist the conditions of water-bloom in somepart of Songhua Lake.

Key words: Crop residue, Soil respiration, Soil microbial biomass