The Effects Of Water Management And Exogenous Ionsincluding Calcium, Phosphorus And Ferric Ion On The Uptake Of Multiple Heavy Metals (or Metalloids) In Rice Plant

The contamination of heavy metals or metalloids,such as antimony(Sb),arsenic(As)and cadmium(Cd)is serious in the soil environment in China.Rice plant is the major food crop in our country.This study was conducted to investigate the effects of different exogenous ions and water management on the migration of Sb,As,Cd and the essential elements within soil-plant system.The exogenous ions included phosphorus(added in the form of NaH2PO4 at the following levels of 200、500 and 1000 mg·kg-1),calcium(added in the form of CaCl2 at the following levels of 20、80 and 200 mg·kg-1),ferric ion(added in the form of FeCl3 at the following levels of 5、10 and 20 mg·kg-1).The water treatment was performed as three modes as follows:flooding all throught the growth period,intermittent irrigation and dry fanning.The purposes of this study were mainly to explore possibilities of using these methods to reduce the accumulation in the edible part of rice plants exposing to multiple heavy metal(metalloid)contamination.The main results are as follows:1、The additions of P,Ca and Fe reduced the concentrations of Sb and Cd(treatment of Ca improved the concentrations of Cd),but increased the concentration of As in soil solution in the early stage of transplanting.After 60d growth of rice plants,high levels of Ca(Ca200)and Fe(Fe20)reduced the Sb concentration in soil solution to be lower than that in control treatment,which might be due to the large uptake by rice plants.The treatments of P200,Ca and Fe also reduced the As concentration in the soil solution in 60d,but other treatment containing Ca,Fe and P showed a limited effects on the soil Cd concentration.The additions of different levels of P could significantly enhance the pH values and the available concentrations of Sb and As in the rhizosphere soil,but reduce the Cd available concentration.The additions of exogenous Ca and Fe had little effects on the avaliable As,Cd and Sb in the rhizosphere soil.Intermittent irrigation and dry fanning could strongly reduce the Cd concentrations in the soil solution compared with the flooding treatment,but they show a weak ability to reduce the concentrations of Sb and As in the soil solution.After the transplanting for 60d,the intermittent irrigation and dry farming treatments reduced the concentrations of Sb and As in the soil solution,but enhanced the concentrations of Cd in soil solution.2、Before transplanting,the addition of P1000 reduced but P200 increased the concentrations of K,Ca,Mg,Mn and Fe in soil solution.The addition of Ca and Fe increased the concentrations of K,Ca and Mn,and the Ca80 and Fe5 treatments showed a better ability to increase the concentrations of K,Ca and Mn than other treatments.After the growth of rice plants for 60d,the addition of P,Ca and Fe decreased the concentrations of Mn and Fe in the soil solution.Low soil moisture content benefit increasing the concentrations of K,Ca and Mg,in which dry farming had the highest but the flooding treatment had the lowest efficiency to increase K,Ca and Mn concentrations in the soil solution3、The additions of P,Ca and Fe and low soil moisture were beneficial to the formation of iron plaque,but the ability of iron plaque to bind heavy metals(metalloids)was found to be relevant to the dose of exgenrous P,Ca and Fe.The additions of P andFe significantly increased the DCB-As,while only P500 treatment increased the concentrations of DCB-Cd and DCB-Sb.However,the addition of P and Fe increased the concentrations of As,Cd and Sb in the roots and shoots of rice,indicating that iron plaque showed a limited role in inhibiting the uptake of As,Cd and Sd in this study..Intermittent irrigation and dry farming increased the concentration of Cd in the iron plaque and the different parts of rice plants,but decreased the concentrations of As and Sbin the iron plaque and the different parts of rice plants.The additions of P,Ca and Fe in most cases increased the concentrations of Mg,K,Fe,Mn and Zn in the iron plaque.Intermittent irrigation and dry farming enhanced the concentration of K in the iron plaque.The increased concentrations of Mg,K,Fe,Mn and Zn failed to significantly decrease their concentrations in the major parts of rice plants.The above mentioned results showed that the concentrations of nutrient elements in different parts of rice plants had no definite causal relationship with their concentrations in iron plaque.4、The addition of P increased the As concentration in different parts of rice plants.The treatment of Ca200 and Fe20 and Intermittent irrigation had a better ability than other treatments to reduce the concentrations of As,Cd and Sb in brown rice.In the aspect of maintaining the concentrations of essential elements in brown rice,the P showed a better ability than Ca and Fe,in which 200 mg·kg-1 P treatment was optimal dosage to keep the concentrations of nutrient elements in the brown rice.