The Dynamical Aspects Of The Photosynthesis Of Egeria Najas Under The Coexistence Of ZnO NPs And Cd²⁺

In order to evaluate the bio-toxicity of nanoparticles more comprehensively,the synergy between nanoparticles and other toxic substances is receiving more and more attention.In this thesis,Egeria najas was used as the test plant to study the effect of the synergy between ZnO NPs and Cd²⁺on the photosynthetic dynamics of aquatic plants.By analyzing the kinetic fluorescence curves of Egeria najas,it was found that the addition of ZnO NPs?spherical,particle size 50 nm?improved the photosynthesis parameters of Egeria najas compared to the treatment with Cd²⁺ solution alone.When the concentration of Cd²⁺ is 2 mg/L,the maximum reduction rate of QA?0M?and the relative fluorescence variable intensity at point J?jV?decreased by 11% and 17%after adding 30 mg/L of ZnO NPs,respectively.The energy used for electron transfer?0ET/ RC?has been increased by 24%,indicating that ZnO NPs enhanced the connectivity between the reaction centers of Egeria najas and promoted the transfer of photoelectrons;the light energy absorbed by unit reaction center?ABS/ RC?and The heat dissipation of unit reaction center?0DI/ RC?decreased by 33% and 34%?P<0.05?,respectively,and the photosynthetic performance index increased particularly,reaching 162%?P <0.05?.This shows that ZnO NPs are improving the utilization of light energy by Egeria najas.At the same time,it improves the overall photosynthetic performance of Egeria najas.In order to further study the mechanism of photosynthetic dynamic changes of Egeria najas under the combined stress of ZnO NPs and Cd²⁺,Cd²⁺ ion selective microelectrode was prepared to monitor the concentration of Cd²⁺ in the culture solution in real time.The results showed that within the first 6 h,the Cd²⁺concentration in the culture solution decreased most obviously.After 8 h,the Cd²⁺concentration gradually stabilized.After 24 hours cultivation of Egeria najas,the initial Cd²⁺ concentration of 1.00 mg/L and 3.00 mg/L decreased by 0.75 mg/L and1.82 mg/L,respectively.When ZnO NPs were added,The decrease of Cd²⁺concentration in these two solutions was significantly reduced to only 0.64 mg/L and1.26 mg/L,respectively.The above results indicate that ZnO NPs can inhibit the absorption of Cd²⁺ by Egeria najas,and the higher the concentration of Cd²⁺,the more obvious the inhibition effect.The inhibition of ZnO NPs on Cd²⁺ uptake by Egeria najas can help to improve the photosynthesis of Egeria najas.In this thesis,by analyzing the kinetic fluorescence curves of Egeria najas and monitoring Cd²⁺ concentration in the culture solution by cadmium ion selectivemicroelectrode,the effect and mechanism of ZnO NPs and Cd²⁺ synergy on photosynthesis of Egeria najas were revealed.The results of this study are of certain significance for finding effective ways to alleviate the phytotoxicity of heavy metal ions.