Influence And Mechanisms Of Silicon On Rice Growth Under Arsenic Stress

Silicon has received extensive attention due to its beneficial role in alleviating plant biotic?abiotic?stress.Rice is a type of silicon-loving crop.Applying silicon can not only promote rice growth,but also alleviate the toxic effects of heavy metals on rice.Now,there have been a lot of reports on the research of silicon amelioration of arsenic toxicity in rice.However,the strong alkalinity of the silicon-containing materials or the influence of the cations on the availability of arsenic in the soil is usually ignored,and the soil and plants are less studied as a whole system.Therefore,systematic research on the effects of silicon on rice cultivation under arsenic stress has important theoretical and practical significance for the repair and utilization of arsenic-contaminated soil and the safe production of rice.In this paper,soil-plants are studied as a whole system on the basis of eliminating the influence of exogenous silicon?Na₂SiO₃?alkaline and accompanying ions?Na⁺?.Through outdoor potted experiment and indoor culture experiment,systematic analysis of the effect of adding exogenous silicon has been taken,including the growth and yield of rice,rice arsenic accumulation,soil solid phase arsenic morphology,soil solid-liquid interface arsenic chemical behavior,arsenic enrichment on soil-plant interface?rice root surface?.This study explores the regulation effect and mechanism of exogenous silicon on arsenic in soil-plant system.The main results and conclusions are as follows:?1?Silicon application can mitigate the toxicity of arsenic to rice.It can promote the growth of rice plants,increase rice yield,and reduce the arsenic content in brown rice.When the amount of silicon added between 100-150mg kg^-1,it can inhibit the stress of arsenic on rice,while the amount of silicon added 50mg kg^-1 had no obvious effect on alleviating arsenic stress in rice.The application of exogenous silicon increases the content of silicon in brown rice and reduces the accumulation of arsenic in brown rice.There is a significant linear negative correlation between the content of silicon and arsenic in brown rice?r=-0.988^*?.?2?Silicon application has a quite small effect on the form of arsenic in the soil solid phase.The content of the iron arsenic?Fe-As?in soil is the highest,accounting for39.97%-41.46%in total arsenic,and the content of the exchangeable arsenic?AE-As?is the least,accounting for 1.11%-1.24%in total arsenic.There is no significant difference in content of the water-type arsenic?H₂O-As?,the exchangeable arsenic?AE-As?,the iron arsenic?Fe-As?,the calcium arsenic?Ca-As?and the occluded arsenic?O-As?between all treatments.?3?Silicon affects the chemical behavior of arsenic at the solid-liquid interface of the soil.To some extent,the application of silicon inhibits the adsorption of arsenic in soil and slowed the reaction rate.The double constant equation and the Elovich equation can well describe the adsorption kinetics of arsenic in soil.The Langmuir equation,the Freundlich equation and the Temkin equation are all suitable for describing the isothermal adsorption characteristics of arsenic in soil.And especially the Freundlich equation has the best fitting effect.Silicon application can reduce the adsorption capacity and intensity of arsenic in soil.The adsorption of arsenic in soil is a spontaneous physical process of endothermic and entropy increase.The application of silicon increases the adsorption free energy change??G⁰?,decreases the enthalpy change??H⁰?and decreases the entropy change??S⁰?during the soil adsorption of arsenic.It means silicon application reduces the spontaneous degree of arsenic adsorption in the soil and reduces the system chaos.?4?Silicon application promotes the formation of iron plaque on root surface of rice.Compared with no silicon treatment,the contents of DCB-Fe and DCB-As in rice root increase significantly in each silicon added treatment,and there is a significant linear positive correlation between them?r=0.970^*?.Application of silicon increases the iron plaque of the root surface,promotes the fixation of arsenic by roots,and reduces the absorption of arsenic by rice roots.In conclusion,the application of silicon has no significant effect on the morphology of soil solid phase arsenic,and it is beneficial to promote the enhancement of arsenic activity in soil solid-liquid interface.However,it can reduce the absorption of arsenic in rice by promoting the formation of iron plaque on the root surface of rice and its fixation of arsenic in soil solution,so as to alleviate the arsenic toxicity of rice.