Cadmium Accumulation Characteristics And Inhibitory Effect Of Quicklime In Rice-Crayfish Coculture Mode

The rice-crayfish co-culture model is an ecological rice cultivation model that combines rice cultivation and Procambarus clarkii cultivation.It is the largest and highest-yield rice-fishing comprehensive cultivation model in China.In recent years,with the rapid development of economy and the acceleration of urbanization and industrialization,the problem of soil heavy metal Cd pollution has become more and more prominent.Therefore,the relationship between water and soil environmental factors and Cd content in rice and crayfish tissues was studied,and the effect of different concentrations of quicklime application on Cd absorption in different tissues and organs of rice and crayfish under rice-crayfish co-culture mode was explored,and then the optimal concentration of quicklime application was determined,which provided theoretical basis and technical support for soil treatment of Cd-contaminated paddy field integrated farming system.The main results are as follows:1.In this study,a rice-crayfish co-culture system with different Cd pollution levels(0～30 mg kg-1)was constructed by adding exogenous cadmium(CdCl2),and the dynamic changes of heavy metal Cd content in soil,water,crayfish and rice were measured during the whole growth period of rice.The results showed that the Cd concentration in rice tissues and crayfish organs increased with the increase of soil Cd concentration.The specific performance is that the Cd concentration in each tissue of rice is:root>stem>leaf≈panicle>grain>brown rice.The jointing stage and heading stage are the key periods for the rapid enrichment of Cd in the aboveground tissues of rice.The concentration of Cd in each organ of crayfish was:hepatopancreas>intestine>gill>shell>abdominal muscle.After 30 days of rice-crayfish symbiosis,Cd began to accumulate in the abdominal muscle of crayfish.Correlation analysis showed that total Cd concentration in soil,available Cd(Cdava)concentration in soil and Cd concentration in water were significantly positively correlated with Cd content in rice tissues and crayfish organs.According to the maximum limit of cadmium pollution in grain(0.2 mg kg-1)and crustacean aquatic animals(0.5 mg kg-1)in China,the soil Cd safety thresholds of rice and crayfish in the rice-crayfish co-culture system were 3.67 mg kg1 and 17.23 mg kg-1,respectively.Therefore,when the soil Cd concentration in the ricecrayfish co-culture system exceeds 3.67 mg kg-1,the safety risk of humans to eat rice from the co-culture system will increase.The Cd pollution model established in this study provides a theoretical basis for the safe production of rice and shrimp in the riceshrimp co-culture system.2.Four lime application concentrations(L0:0 kg hm-2,L1:500 kg hm-2,L2:1000 kg hm-2,L3:1500 kg hm-2)were set up to study the effect of different concentrations of lime application on Cd absorption in different tissues and organs of rice and crayfish under rice-crayfish co-culture mode,and then determine the optimal lime application concentration.The results showed that the application of quicklime could significantly increase the pH value in soil and water environment under the rice-crayfish co-culture mode,and the pH value began to rise rapidly 10 days after the application of quicklime,and gradually stabilized after 20 days.L3 treatment had the best effect on the regulation of soil Cdava concentration,and the maximum decrease could reach 61.46%compared with CK.The application of quicklime had a significant effect on the control of rice panicles with high soil basic Cd pollution concentration,and significantly reduced the Cd in rice<0.05).The Cd content in rice decreased by about 13.52%～72.11%,and the L3 treatment had the best control effect.The application of quicklime could reduce the Cd concentration in hepatopancreas and abdominal muscle of crayfish under the rice-crayfish co-culture mode.The application of quicklime in hepatopancreas and abdominal muscle decreased by 9.77%～92.36%and 2.97%～94.15%,respectively.L3 treatment could significantly reduce the concentration of Cd in hepatopancreas and abdominal muscle of crayfish.After the application of lime,the concentration of Cd in hepatopancreas and abdominal muscle of crayfish was 0.0968 mg kg-1 and 0.0018 mg kg-1,respectively,which were much lower than the Cd pollution limit of crustacean aquatic products in China.Therefore,the application of 1500 kg hm-2 lime can well control the enrichment of Cd in rice grains and crayfish hepatopancreas and abdominal muscles,and the safety risk of agricultural products is greatly reduced.