Effect Of Exogenous Organic Carbon On Barrier Effect And Mechanism Of Cadmium In Rice

The area of cultivated land contaminated with heavy metals accounts for about 20% in China,it is difficult,time-consuming and costly to repair,which brings great difficulties and challenges to pollution control.Rice absorbs cadmium and has a strong grain accumulation,soil-rice plant-rice migration accumulation is the main way to harm human health.Signal material conduction in vivo can affect the concentration of cadmium in rice.Previous studies in this laboratory show that exogenous organic carbon can effectively inhibit cadmium accumulation in rice and is an effective way to prevent and control cadmium pollution in rice fields.On the basis of previous research,this study further develops the optimization of the organic carbon spraying method and discusses its blocking mechanism.It includes the optimal concentration of organic carbon spraying under different levels of cadmium pollution,the effect of organic carbon spraying on cadmium accumulation and manganese absorption at different growth stages of rice,the physiological and biochemical indexes of organic carbon spraying on rice and the distribution of cadmium and manganese in leaf organelles to provide technical support and theoretical basis for preventing and controlling cadmium pollution in rice fields by spraying organic carbon.The main findings are as follows:Pot experiments on the accumulation of cadmium in rice by TS spraying at different levels of cadmium pollution showed that the content of cadmium in brown rice was significantly reduced and the decrease increased with the increase of cadmium concentration in soil.The reduction can be as much as 35% at low pollution levels and 55%-66% at medium and high pollution levels;At the same soil Cd level,the difference between the treatment of TS with 5 different concentrations was relatively small,and the concentration of TS with the greatest decrease of Cd in brown rice was different in different soil levels.On the whole,the TS spray concentration of 0.6 mmol/L has good effect at different pollution levels.According to the distribution of Cadmium accumulation in rice,the proportion of Cadmium in rice straw treated by spraying TS increased in different degrees,while that in saber leaf,brown rice and rice husk decreased and increased with the increase of soil Cadmium content.Determination of biomass and rice yield at harvest showed that spraying TS increased rice growth,increased rice yield and increased rice yield by 17%-39% at high soil cadmium contamination levels(Cd 6.2331 mg/kg).The results of pot experiments on cadmium accumulation and manganese absorption in rice brown rice by spraying three types of organic carbon(FS,CS and BS)at different concentrations in paddy soils contaminated with cadmium(Cd 2.7149 mg/kg)showed that,The application of different concentrations of FS,CS and BS significantly reduced the cadmium content of brown rice by 65.8%-72.1%、54.6%-78.4%、67.8%-77.9%,while the manganese content of brown rice decreased by 2.2%-18.7%、2.5%-15.3%、4.0%-13.3% respectively.The optimal spray concentration is related to the type of organic carbon.There was no significant difference in Cd concentration between 5 different spray concentration treatments of FS,but Mn content decreased with the increase of FS spray concentration.Cadmium decreased most in brown rice treated with CS spraying concentration of 0.6 mmol/L,but there was no significant difference in manganese content between different spraying concentration treatments.The treatment of cadmium in brown rice with BS spraying concentration of 0.2 mmol/L showed the largest decrease,but the difference was not significant with the treatment of 0.4 mmol/L and 0.8 mmol/L,and there was no significant difference in manganese content between the treatment of brown rice with different spraying concentration.The effects of FS on cadmium and manganese content of rice in pot at different growth stages(Ⅰ-Tillering period;Ⅱ-Tillering period and Boost stage;Ⅲ-Tillering period、Boost stage and grouting period)showed that the cadmium content of rice decreased with the increase of spraying times.The reduction of Cd was 63.16%-73.36% 、 44.25%-53.18%、32.11%-43.48% respectively in the treatment of Ⅲ、Ⅱ、Ⅰ.The treatment of Ⅲ has the best barrier effect on cadmium concentration in brown rice,but the difference between spraying concentration is small.The decrease of Mn content in brown rice showed a similar rule.The decrease of Mn was 7.33%-10.86%、4.49%-12.08%、0.80%-4.89%,but the decrease was small.The results of water soluble protein and related enzyme activity in potted rice leaves at different levels of cadmium showed that the content of proline and protein and the activities of peroxidase(POD),peroxisome(CAT)and superoxide dismutase(SOD)in potted rice leaves could be improved by using FS.The content of proline and the activities of POD and CAT in rice leaves increased with the increase of cadmium in soil.Determination of Cd and Mn in organelles of rice leaves at grouting stage showed that the contents of Cd and Mn in organelles were as follow: F1(cell wall)>F5(ribosome and intracellular solutes)>F2(chloroplast)>F3(nucleus)≈F4(mitochondria);Compared with spraying water,the Cd content in rice leaves increased from 34.52% to 37.29%、38.75% to 45.34%、52.31% to 57.14%、56.44 to 63.62%、64.94% to 68.13% respectively from low to high concentration cadmium soil.The results showed that the ability of Cd retention by injection FS could be improved effectively.The effect of FS injection on manganese distribution in cell walls and organelles is similar to that of cadmium.The above results provide scientific basis for further revealing the accumulation of Cadmium in rice by exogenous organic carbon blocking,and provide technical support for preventing and controlling Cadmium pollution in rice fields and ensuring rice food safety.