Mechanism Of Silicon-Iron Hydrogen Oxides To Alleviate Cadmium Stress In Rice

In recent years,the intensification of cadmium pollution in farmland soils has affected the quality and safety of agricultural products.Cadmium enters the body through the food chain and can seriously damage the kidneys,cardiovascular,musculoskeletal system and female reproductive system.Therefore,it is imperative to control the cadmium pollution in farmland soil and ensure the safety of agricultural products.Silicic acid and iron hydroxide have reduced the bioavailability of cadmium in soil,and thus alleviated the stress of cadmium on rice.However,its chemical mechanism is not completely clear.Therefore,the study on the effect of silicon and iron hydroxide coexistence on cadmium toxicity in rice and its mechanism have important theoretical significance for revealing the mechanism of silicon to reduce the bioavailability of soil cadmium.Based on the CD-MUSIC model,this paper studies the surface complexation morphology of cadmium silicon-iron hydroxide,and aims to explore the soil chemical mechanism of cadmium toxicity alleviation in the coexistence of silicon and iron hydroxide.In this paper,high purity silicate-treated iron hydroxide(Si-Fh,Si-Goe)were obtained by chemical methods,and their physical and chemical properties were characterized by X-ray diffraction,infrared spectroscopy,scanning electron microscopy,specific surface area measurement and acid-base potentiometric titration.The hydroponic and isothermal adsorption-desorption experiments were combined with the CD-MUSIC model to confirm the effect of silicon-iron hydroxide on cadmium toxicity in rice,and to reveal the mechanism of silicon on the adsorption behavior of cadmium in acid paddy soil.The main conclusions are as follows:1.Silicon-iron hydroxide can significantly alleviate cadmium stress in rice.Treatment of silicon-iron hydroxide and iron hydroxide under cadmium stress reduced cadmium content(P<0.05),CAT activity(P<0.05),POD activity(P<0.05)and MDA content(P<0.05).It relieves membrane lipid peroxidation and lignification;complete root tissue differentiation,clear vascular bundle ring pattern,and tight cell structure;promote rice seedling growth,enhance its ability to resist cadmium stress,and alleviate the effect of silicon-iron hydroxide treatment better than iron hydroxide.2.Silicon-iron hydroxide can significantly promote the adsorption of cadmium.The adsorption capacity of cadmium in each treatment,silicon-iron hydroxide phase promoted cadmium adsorption to inhibit cadmium desorption compared with iron hydroxide(P<0.05);cadmium adsorption amount was positively correlated with pH;both nonlinear isotherm adsorption Langmuir equation and Freundlich equation can better fit the adsorption of cadmium.But the fitting effect of Freundlich equation is better than that of Langmuir equation.The cadmium adsorption of iron hydroxide tends to be non-uniform monolayer adsorption.3.Based on CD-MUSIC model fitting,it is shown that the ternary surface complex of cadmium forming iron hydroxide-silicon-cadmium on the surface of silicon-iron hydroxide is the soil chemical mechanism of silicon to alleviate the toxicity of cadmium in acid paddy soil.The silicon-iron hydroxide has more surface hydroxyl groups than iron hydroxide;the silicon-iron hydroxide phase shifts to the left of the charge zero of the iron hydroxide,and the surface negative charge increases.Silicon is mainly adsorbed on the surface of iron hydroxide by double-dentate dinuclear and monodentate mononuclear complexes.The main distribution of cadmium on the surface of iron hydroxide is double-dentate dinuclear adsorption,Cadmium form an iron hydroxide-silicon-cadmium ternary surface complex on the surface of the silicon-iron hydroxide.In summary,silicon-iron hydroxide can effectively alleviate cadmium stress in rice,reduce cadmium content in rice,alleviate membrane lipid peroxidation and lignification,enhance root tissue differentiation and enhance cadmium resistance;cadmium is mainly electrostatically adsorbed and The coordination adsorption method forms an iron hydroxide-silicon-cadmium ternary surface complex on the surface of the silicon-iron hydroxide without being absorbed by rice seeding.