Differences Of Cd Uptake By Rice And Agronomic Remediation Of Cd-contaminated Soil

It has attracted the attention of Cadmium pollution in paddy fields,which has harmful influence on the quality of rice and the health of human and it is relatively weakness of technology and theory to reduce the rice content of cadmium.Therefore,this study is aimed at controlling the uptake of Cd by rice based on the following three aspects of agronomic measures including the rice varieties,water regulation and fertilizers application.In this study,the coupling relationship between the Cd subcellular accumulation characteristic and its reconciliation with cadmium tolerancewere among different Cd sensitivity rice cultivars was investigated based on the method of desorption of subcellular components in living root cells.The effects of four different water managements and four kinds of nitrogen fertilizers on soil pH,soil bio-availability of Cd and Cd uptake were also investigated respectively in this study which is aimed at providing some theoretical and technical of reducing the cadmium content of rice and to achieve the purpose of repairing contaminated rice fields.The main results are as follows:1.The Cd content of the grains was significantly different,ranging from 0.09mg/kg to 0.48mg/kg among Six different Cd-sensitive rice varieties.The orders of translocation factors for Cd from roots to shoots(TF_shoots)and roots to grains(TF_grains)are basically the same as that of Cd content in their grains.The larger cultivars are Zhongxiangzao 17?R1?,Jiayu 211?R2?,the smaller ones are Zhuliangyou 211?R5?,Jinyou 463?R6?.There were significant differences in the Cd concentration of the root cell walls of the six kinds of rice varieties under the soils of three Cd concentrations?CK,T1,T2?,respectively:0.763mg/kg?FW⁰.997mg/kg?FW,3.011mg/kg?FW⁵.717 mg/kg?FW and 3.687mg/kg?FW⁷.122mg/kg?FW.The order of Cd content in the root cell wall of rice was opposite to that in rice grain Cd concentration,indicating that the adsorption of cadmium on rice root cell wall may be one of the main mechanisms of low-absorption cultivars to adapt to Cd stress.The results showed that the content of Cd in the cell wall of the rice roots was significantly increased after removing the pectin composition,and the Cd content in the cell wall of R1 had the largest increase and the smallest increase of R5.Removal of pectin and hemicellulose significantly reduced the content of Cd in the cell walls of different rice roots.Among them,the maximum adsorption capacity of Cd was decreased to 59.6%by the removal of pectin and hemicellulose from rice root cell wall of R5,the smallest is that of R1?8.5%?.This is the same as that of rice grain,which shows that hemicellulose is an important part of rice root cell wall for Cd fixation.2.Two kinds of rice varieties with different Cd sensitivity and two typical paddy soils were selected for different water management experiments.The water managements modes included general water managements?CK?,water flooding in all growth periods?WF?,dry cultivation in all growth periods?DC?,alternate drying and wetting?DW?.The results showed that different water managements had a significant effect on the availability of soil Cd and the Cd contents in rice grains.And the order is basically the same,from low to high respectively:WF<DW<CK<DC.Compared with CK,the decrease of soil available cadmium and cadmium content in rice was the largest of WF,which could reach37.12%and 46.37%respectively,and those of DC were significantly increased by 28.36%and 33.06%,respectively.And the soil available Cd under different water managements showed significant correlations with stem and leaf,grain and root of rice,which indicated that the flooding in the whole growth period could reduce the Cd content in different parts of rice by reducing the effectiveness of soil Cd.3.There were significant differences in the contents of Cd in the stems and leaves,roots and grains of the four fertilizers including urea?CK?,NH₄Cl?A?,?NH₄?₂SO₄?B?and?NH₄?₂HPO₄?C?.In the treatment of four kinds of fertilizers,the contents of Cd in all parts of rice were A>CK>B>C from high to low.Compared with CK,the cadmium content of rice in treatment of A was significantly increased,and it increase was in the range of 10.77%⁵2.23%,and that in the treatments of B and C was significantly decreased,the reduction rates were 6.25%¹8.43%and 12.96%³5.55%respectively.The effect of the four fertilizers on available cadmium content of soil was similar to cadmium content of rice.The four kinds of fertilizers had a significant effect on the pH of the soil,but the order was in the different order as that of rice cadmium content and available soil cadmium content.The order was C>CK>B>A.Compared with CK,the soil pH in Jiaxing and Xiangtan in the treatment of A reduced by0.37 and 0.15 units,respectively.And that in the treatment of B decreased 0.29 and 0.15 units respectively,and that in the treatment of B decreased increased by 0.16 and 0.11 units respectively.Soil pH was significantly different but it was not associated with the enrichment ability of Cd in rice significantly in the four fertilizer treatments.This perhaps was because that after adding ammonium sulfate,the soil acidification is stronger,but in the flooded state CdS can be produced to reduce the soil availability,so that the cadmium content of rice is low.The reason for the difference of cadmium deficiency in four fertilizers is also related to the association of anions with cadmium in soil.Therefore,in order to reduce the accumulation of Cd in rice and to improve the food safety of rice,we should use cadmium low-absorption rice cultivars,and use the water management mode of flooding during the whole growth period.When chosing nitrogen fertilizer,we should avoid using NH₄Cl,however,?NH₄?₂SO₄ and?NH₄?₂HPO₄ were recommended.