Effects Of Silicon Application On Arsenic Uptake,Translocation And Accumulation In Rice

Rice is one of the staple foodcrops.The ability of arsenic accumulation in rice is much higher than other upland cereals for flooding condition,which would pose a health risk for human being via food chain.It is well known that the application of silicon could reduce effectively the accumulation of arsenic in rice grains.It is very important to screen the appropriate application rate of silicon for paddy rice growm in arsenic contaminated soils with different As levels.Therefore,two hydroponic experiments were conducted to study the effects of Si application rates on the uptake,efflux,translocation and accumulation of arsenic in rice seedlings when phosphorus?P?was supplied at one level or different levels.Furthermore,one soil pot experiment was carried out to investigate the impacts of Si application rates on the accumulation of total arsenic and inorganic arsenic in brown rice,polished rice and rice bran when rice grew in the lightly,moderately and heavily arsenic-contaminated soil.The main results are shown as follows:1.In the hydroponic experiment with the same P concentration in nutrient solution,when rice seedlings were exposed in nutrient solution with 10?mol/L As?III?or As?V?for12-48 h,the ratio of Si/As at 200:1?2.0 mmol SiO₂/L?significantly inhibited arsenic uptake,As?III?efflux,translocation of As?III?from root to shoot and As?III?accumulation in rice shoot.2.In the hydroponic experiment with different P levels in nutrient solution,when rice was exposed to different concentrations of silicon?0.0,1.0,2.0 mmol/L?and phosphorus?0,46,91,182,273?mol/L?,there was a significant positive correlation between the uptake of As?V?and the efflux of As?III?in rice with 10?mol/L As?V?nutrient solution for 48 h.Phosphorus is the main factor of inhibiting the uptake of As?V?and the efflux of As?III?,accouting for 64.0%-87.5%and 47.2%-61.2%.Silicon is the main factor inhibiting the translocation of As?III?from root to shoot by 55.8%-84.7%.The high concentration of silicon application significantly inhibited the translocation of As?III?from root to shoot in rice and accumulation of arsenic in rice shoot.The accumulation of arsenic in shoot of rice was not affected by the phosphorus supply levels.3.The appropriate Si application rates to reduce the accumulation of total arsenic and inorganic arsenic and arsenic species in rice edible parts was certified in lightly,moderately and heavily arsenic-contaminated soil using pot experiment.The results showed that in lightly arsenic-contaminated soil,the application rates of silicon?SiO₂?at25 mg/kg and 50 mg/kg significantly reduced the total arsenic and inorganic arsenic concentrations in brown rice and rice bran by 33.2%and 61.0%,respectively?P<0.05?.In moderately arsenic-contaminated soil,the concentration of inorganic arsenic in the treatment of 50 mg/kg was lower in rice bran,and the silicon application exceeds 100mg/kg increased the concentrations of inorganic arsenic in the rice bran,accounting for52.1%and 30.1%,respectively?P<0.05?.In heavily arsenic-contaminated soil,the application of 25 mg/kg of silicon significantly reduced the inorganic arsenic concentration in brown rice by 30.9%,while the application of silicon concentration at 400 mg/kg significantly increased the inorganic arsenic concentration in brown rice by 31.9%?P<0.05?.In addition,the silicon application of 100 mg/kg also increased the inorganic arsenic concentration in rice bran by 55.3%.Therefore,in moderately and heavily arsenic-contaminated soil,high silicon application??100 mg/kg?increased the accumulation of inorganic arsenic in the edible parts of rice.In sammary,high concentration of silicon reduced the accumulation of arsenic in rice shoots in the hydroponic experiment of rice seedling stage.However,high silicon application increased the accumulation of inorganic arsenic in the edible parts of rice grown in moderately and heavily arsenic-contaminated soil.Considering the accumulation of total arsenic and inorganic arsenic concentrations in edible parts of rice,the suitable amounts of silicon for rice growth in lightly arsenic-contaminated soil ranged at 25-50 mg SiO₂/kg,50 mg SiO₂/kg in moderately arsenic-contaminated soil,and 25 mg SiO₂/kg in heavily arsenic-contaminated soil,high rate of silicon application increased the health risk of arsenic in the edible parts of rice.