Objective To investigate the effect of iron on the growth,physiology and photosynthesis of cyanobacteria.Methods A gradient of iron concentrations was employed to investigate the growth,photo-pigments(chlorophyll A and phycocyanin),and cell chemical contents(C,N,P)of Microcystis aeruginosa in response to different iron additions.Results The specific growth rate during the exponential growth phase,as well as the cell chlorophyll Aand the phycocyanin content,was limited by iron below 12.3 μmol Fe L-1.The growth was inhibited when the iron concentration was at 24.6 μmol Fe L-1.The cell chlorophyll A and the phycocyanin content were saturated when the iron concentration was above 12.3 μmol Fe L-1 and declined slightly at 24.6 μmol Fe L-1.At a low iron concentration(about 6.15 μmol Fe L-1 and less),the cell nitrogen and carbohydrate content were iron limited,and the variation of the cell phosphorus content was similar to that of the nitrogen and carbohydrate,with a transition point of 12.3 μmol Fe L-1.Conclusion The variation of cynobacteria growth is synchronous with that of the photo-pigments or the cell chemical content,and there exist relationships among photosynthesis,growth and internal chemical content,which could be useful for the growth estimation from the cell characteristics. Objective To investigate the effect of iron on the growth, physiology and photosynthesis of cyanobacteria. Methods A gradient of iron concentrations was employed to investigate the growth, photo-pigments (chlorophyll A and phycocyanin), and cell chemical contents (C, N, P ) of Microcystis aeruginosa in response to different iron additions. Results of the specific growth rate during the exponential growth phase, as well as the cell chlorophyll A and the phycocyanin content, was limited by iron below 12.3 μmol Fe L-1.The growth was rendered when the iron concentration was at 24.6 μmol Fe L-1. The cell chlorophyll A and the phycocyanin content were saturated when the iron concentration was above 12.3 μmol Fe L-1 and declined slightly at 24.6 μmol Fe L-1. At low iron concentration (about 6.15 μmol Fe L-1 and less), the cell nitrogen and carbohydrate content were iron limited, and the variation of the cell phosphorus content was similar to that of the nitrogen and carbohydrate, with a transition point of 12.3 μmol Fe L-1.Conclusion The variation of cynobacteria growth is synchronous with that of the photo-pigments or the cell chemical content, and there exists relationships among photosynthesis, growth and internal chemical content, which could be useful for the growth estimation from the cell characteristics.