| As in soil exists in different forms,including water soluble As,exchangeable As,aluminum As,iron As,calcium As and closed storage As.Among them,Al-type As,Fe-type As,Ca-type As and closed-storage As have lower bioavailability,while water-soluble As and exchange As are easily absorbed by plants and have higher bioavailability.The absorption and accumulation of As by rice can be reduced by reducing the bioavailability of As in soil.Studying the process of rice As absorption and brown rice As accumulation is the key to solve the problem of rice As pollution.The difference of nutrition requirement in different growth stages of rice results in the difference of As absorption and accumulation in different growth stages.In this study,the effects of As stress on As accumulation in brown rice at different growth stages were determined through hydroponic experiment,and the key growth period of As accumulation in brown rice was determined;Then,in the key growth period of As accumulation in brown rice,the co-application of calcium carbonate,iron powder and potassium silicate(LIS)in pot experiment and potassium silicate in field experiment were used to further regulate the absorption and accumulation of As in rice.The main results were as follows:1.The results of hydroponics experiment of adding exogenous As in single growth stage of rice(tillering stage,jointing stage,booting stage,filling stage,wax ripening stage and mature stage)showed that booting stage and filling stage were the key growth stages of As accumulation in brown rice.Under As stress(20 μg·L-1)at booting stage only,As content and As accumulation in brown rice were the highest,which were 0.24 mg·kg-1 and 4.5μg·pot-1,respectively,followed by filling stage,which were 0.17 mg-kg-1 and 3.4 μg·pot-1,respectively.By analyzing the As accumulation of brown rice in different growth stages,it was found that the relative contribution rates of booting stage and filling stage to As accumulation of brown rice were 40.3%and 26.0%,respectively.Therefore,As in brown rice mainly comes from booting stage and filling stage.2.The results of pot experiment of applying amendment LIS in the critical growth period of As accumulation in brown rice showed that applying amendment LIS at booting stage and filling stage would significantly reduce the absorption and accumulation of As in rice.Compared with the control,the application of LIS at the critical growth stage of As accumulation in brown rice significantly increased soil pH by 0.28～0.76 units(p<0.05).Application of LIS at booting stage,grain filling stage,booting stage,and grain filling stage significantly reduced As content in all parts of rice,especially As content in brown rice(p<0.05)by 15.9%～20.8%,15.2%～16.9%,and 18.5%～20.1%,respectively.Therefore,it is an effective method to reduce As content in rice by applying amendment LIS at the critical growth stage.3.The results of field experiment with potassium silicate at the key growth stage of As accumulation in brown rice showed that potassium silicate at booting stage and filling stage could increase rice yield and Fe content in iron film on root surface,and reduce inorganic As content in brown rice.The yield of brown rice increased by 22.6%with the application of 20 kg·hm-2 potassium silicate at the grain filling stage(p<0.05).Compared with the control,when 20 kg·hm-2 potassium silicate was applied at booting stage,grain filling stage,booting stage,and grain filling stage at the same time,the iron Film Fe content of rice root surface increased by 84.3%,16.9%,and 56.2%respectively(p<0.05),and the As content of brown rice decreased by 33.0%,12.8%and 15.0%respectively(p<0.05).Especially at the booting stage,the content of inorganic As in brown rice with 20 kg·hm-2 potassium silicate was the lowest,which was 0.21 mg·kg-1.Therefore,applying potassium silicate at booting stage is an effective method to reduce inorganic As content in brown rice. |
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