Physiological and biochemical responses of Microcystis aeruginosa to phosphine(PH3) under elevated CO2

Phosphine(PH) 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 PHunder elevated COconcentration,Microcystis aeruginosa was used in the coupling treatment of 1000 ppmv COand PHat 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 COand PH3 at different concentrations(7.51×10,2.48×10,7.51×10mg/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 COalone,and their enhancement increased with the increase in PH3 concentrations.The total antioxidant capacity(T-AOC) in the coupling treatment with COand PH3 of 2.48×10mg/L and 7.51×10mg/L showed increasing tendency,compared to the treatment with PHalone.Additionally,the coupling treatment with 1000 ppmv COand PH3 also altered the pH and DO level in the culture medium.In this regard,the coupling treatment with COand PHat 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 COlevel,our research laid a foundation for the scientific understanding of the correlation between PHand cyanobacteria blooms.