Phosphine (PH3) is an important factor driving the outbreak of cyanobacterial blooms that produce toxic microcystin threating human health.To clarify the physiological and biochemical responses of cyanobacteria to PH3 under elevated CO2 concentration,Microcystis aeruginosa was used in the coupling treatment of 1000 ppmv CO2 and PH3 at different concentrations respectively.The chlorophyll a (Chl-a),carotenoid,net photosynthetic rate and total protein of M.aeruginosa exhibited evidently increasing tendency under the coupling treatment of 1000 ppmv CO2 and PH3 at different concentrations (7.51 × 10-3,2.48 × 10-2,7.51 × 10-2 mg/L).The coupling treatments resulted in the higher concentrations of Chl-a and carotenoid of M.aeruginosa,compared to those in the control and the treatment with CO2 alone,and their enhancement increased with the increase in PH3 concentrations.The total antioxidant capacity (T-AOC) in the coupling treatment with CO2 and PH3 of 2.48 × 10-2 mg/L and 7.51 × 10-3 mg/L showed increasing tendency,compared to the treatment with PH3 alone.Additionally,the coupling treatment with 1000 ppmv CO2 and PH3 also altered the pH and DO level in the culture medium.In this regard,the coupling treatment with CO2 and PH3 at an appropriate concentration can enhance the resistance of M.aeruginosa to PH3 toxicity and is beneficial to the reproduction of M.aeruginosa,presumably resulting in potential for the outbreak of cyanobacteria bloom.Given the concern about global warming and the increase in atmospheric CO2 level,our research laid a foundation for the scientific understanding of the correlation between PH3 and cyanobacteria blooms.