Abstract:The effects of metal ions on acidic and alkaline phosphatase (ACPase and ALPase) activities and kinetic parameters of periphytic biofilm in paddy fields were studied. The results suggested that both K+ and Na+ had no significant effect on ACPase and ALPase activities in the concentration range of 0-1.0 mmol/L while both Ca2+ and Mg2+ had activating effects on ACPase and ALPase activities, which increased phosphatase activity by 14.1% and 46.7%, respectively. The metal ions of Zn2+, Cu2+, Mn2+, Al3+ and Ag+ all had inhibitory effect on ACPase and ALPase activities. While Co2+ could promote ACPase and ALPase activities at low concentration, but inhibit them at high concentration. And Cr6+ promoted ACPase activity at 0.1 mmol/L, while inhibited ACPase activity in the concentration range of 0.25-1.0 mmol/L. The addition of Mg2+ enhanced the affinity and catalytic efficiency of ACPase with substrates. The inhibitory effect of Cu2+ on ACPase and ALPase activities was mainly considered as non-competitive inhibition. Although Zn2+ increased the affinity of ACPase with substrate, it reduced the affinity and catalytic efficiency of ALPase with substrate. The effect of metal ions on enzyme activity varied with the type and concentration of metal ions, and the type of phosphatase. It is mainly achieved by binding with the site or substrate of enzyme activity, changing the affinity between enzyme activity and substrate, and influencing the expression of enzyme genes. The results can provide a theoretical basis for assessing the role of periphytic biofilm in the biogeochemical cycle of phosphorus in paddy fields, and the possible risk of heavy metal contamination in paddy fields.