Effects Of Foliar Application Of Silicon On Arsenic Uptake And Accumulation In Rice

As one of the staple crops,rice has strong ability of arsenic uptake and translocation.It has been shown that application of silicon in soil can significantly reduce the accumulation of arsenic in rice,but Si addition in soil increased the arsenic concentrations in soil solution and the risk of arsenic stress on rice as well.Does foliar application of silicon reduce the uptake and accumulation of arsenic in rice?And reduce the risk of human health?Based on this,a serial of experiments were carried out to investigate the effects of foliar application Si on arsenic uptake and accumulation in rice.First,to verify whether silicon can transport in the phloem of rice after foliar application of silicon,and to study effects of foliar application of silicon on rice uptake and tanslocation of As?III?,As?V?,MMA?V?and DMA?V?.Second,to explore the effects of different foliar silicon amendents on arsenic accumulation in rice seedlings.Finally,the soil culture experiment during the whole growth period was conducted to study the influence mechanism of foliar silicon amendents on arsenic accumulation and variation of arsenic species in brown rice to screen the suitable foliar silicon amendents.The main results were shown as follows:?1?Foliar application of silicon increased the Si concentrations in the shoots and roots of rice seedlings,demonstrating that silicon could transport from shoots to roots through phloem,and it also plays a role in inhibiting the absorption of arsenic in rice.When rice seedlings was sprayed with Si and exposed to the growth medium containing As?III?,As?V?,MMA?V?and DMA?V?for 48 h,respectively,the results showed that foliar application of silicon reduced the arsenic uptake capacity of rice.Under the treatments of As?V?and MMA?V?,foliar application of silicon significantly reduced the uptake of arsenic by rice,accounting for 29.08%and 35.17%?P<0.05?.Whether or not silicon is applied on the rice leaf,the transport capacity of arsenic species in rice followed the trend of DMA?V?>As?III?>As?V?>MMA?V?,which indicates that DMA?V?could be transportrd to the shoots efficiently.?2?The effects of different foliar silicon amendents on arsenic accumulation in rice seedlings were studied using nutrient solution culture.The results showed that the application of all foliar silicon amendents reduced the concentrations of arsenic in rice root,and the effect of spraying Na₂SiO₃ on arsenic reduction in rice was better than that of K₂SiO₃.The application of Na₂SiO₃+rhamnolipid on shoots was the best pathway to inhibit arsenic uptake in rice seedlings,which significantly decreased total arsenic by25.35%and 33.10%in roots and shoots,respectively.This amendent of Si also reduced the levels of As?III?in the shoots and roots by 27.74%and 21.50%,respectively.The transfer factor of arsenic in rice can also reduced by 10.51%.?3?The results from the soil pot experiment during the whole growth period showed that foliar application of silicon amendents significantly reduced arsenic accumulation in rice straw and brown rice,as well as inorganic arsenic and DMA?V?levels in brown rice.It also changed the proportions of inorganic arsenic and DMA?V?in brown rice.K₂SiO₃+Tween-80 and Na₂SiO₃+Tween-80 amendents were better to decrease the levels of arsenic in straw and brown rice.In summary,silicon could transport from shoots to roots through phloem sap,which could inhibit arsenic uptake and translocation,and reduce arsenic accumulation in edible parts of rice.The silicon foliar amendents with rhamnolipid and Twain-80 as surfactant had the better effect to reduce arsenic accumulation in rice.