Effects Of Sulfur,Chlorine,Iron,Manganese And Organic Fertilizer On Uptake And Transfer Of Soil Cadmium (Cd) By Rice Plant

Cadmium is a non-essential element for plant growth and a toxic heavy metal element.Soil and agricultural products contaminated with cadmium pose a threat to human health.At the same time,cadmium is absorbed and enriched by crops,which affects the quality of agricultural products.Remediation of heavy metal cadmium contaminated soil,reducing the absorption of cadmium by crops,and ensuring the quality and safety of agricultural products are one of the main tasks of the current soil environment research.This study relied on long-term fertilization experiments,indoor cultivation and analytical experiments to study the effects of anions Cl^-and SO4^2-,metallic elements Fe and Mn,long-term application of organic fertilizers,green manures,and chemical fertilizers on the accumulation and availability of heavy metal cadmium in soil and on the absorption of cadmium in rice.With a view to providing theoretical and technical support for the treatment of paddy soil contaminated with heavy metal cadmium.1.Cadmium in rice is affected by fertilizer-borne chloride and sulfate:long-term field versus pot experiments.Cl-and SO4^2-are the accompanying ions of potassium fertilizers in conventional potash fertilizer.They enter the soil with the application of potash fertilizer.After long-term application,they will accumulate in the soil and have a certain effect on the effectiveness of soil cadmium.At the same time,both are the physiological functions of rice.Different nutrients have different effects on the transfer of cadmium from soil to rice and distribution in rice plants.Through the 43-year long-term Cl^-and SO4^2-long-term experiment at Qiyang red soil experimental station.The determination of heavy metal cadmium in the soil and rice grains,and the analysis of the soil EDTA-Cd analysis showed that the long-term application of Cl^-containing fertilizers in rice grain cadmium content was72.7%higher than the conventional fertilizer treatment（CF）;while the long-term application of SO4^2-fertilizer treatment in rice grain showed no significance different from the CF.EDTA-Cd content in Cl^-treatment was 60%higher than SO4^2-treatment.The results of the short-term pot experiment on the same soil showed that the cadmium content in the root system of Cl^-fertilizer treatment was 7.4%higher than that in the SO4^2-treatment.While the cadmium content in the stem and leaf was more than twice that in the Cl^-treatment than the SO4^2-treatment.This indicating that Cl^-promoting cadmium from the soil has a strong ability to transfer to plants,especially the ability to promote the transfer of cadmium to the aboveground plant parts.2.Effect of long term application of chemical fertilizers and manure on heavy metals accumulations in rice grain and paddy soil.Heavy metals contamination in paddy soil is a serious worldwide issue because it can cause health risks via food chain.The present long-term field experiment was established in 1988 at paddy field in Hangzhou for 23 years to know the impact of pig manure and inorganic fertilizers on bioavailability and accumulation of heavy metals in soil and uptake by rice plant.The fertilizer treatment in the long term experiments were CK,N2,N2P,N2K,N2PK,N2PK（GM）,M,N1PKM,N2PKM,N3PKM and N2+M.The contents of heavy metals Cd,Pb,Zn,Cu,Cr and Ni in the soil and rice grains were measured,and the results showed that the contents of Cd,Zn and Cu in the soil treated with long-term application of green manure and organic fertilizer combined with inorganic fertilizers were significant higher than the chemical fertilizer treatment,the average was 2.13,0.53 and 0.93 times higher.While the soil Pb,Ni and Cr content did not reflect the significant difference between the organic fertilizer treatment and the chemical fertilizer treatment.Long-term application of organic fertilizer and combined application of organic and inorganic fertilizers,inorganic fertilizers combined with green manure treatment enhanced soil EDTA extractable Cd,Pb,Zn and Cr content and significantly higher than chemical fertilizer treatment,respectively,on average 4.46 times,0.96 times,3.87 times,and1.28 times,times respectively.The content of Ni and Cr extracted by soil EDTA did not reflect the significant difference between organic fertilizer treatment and chemical fertilizer treatment.Long-term application of organic fertilizers and organic-inorganic fertilizers combined treatment of rice grains Cd and Cu content was significantly higher than that of chemical fertilizer treatment with an average of 1.11 times and 60.7%higher respectively.Inorganic fertilizer combined with green manure treatment of rice grain Cd content was significantly higher than chemical fertilizer treatment 1.65 times.However,the content of other heavy metals in rice grains did not show a significant difference between the treatment of organic fertilizer and chemical fertilizer.3.Effects of Fe and Mn cations on Cd uptake by rice plant in hydroponic culture experiment:Manganese and iron are both nutritional elements of rice and participate in the physiological process of rice.Hydroponic experiment results show that the addition of manganese and iron in the culture solution can promote the growth of rice.The biomass of rice added with iron increased by an average of 77%,and the biomass of rice added with manganese increased by an average of 17.3%.The content of Fe and Mn in the culture solution was significantly reduced Cd in rice roots and stems,and the decrease of Cd concentration increased significantly with the increase of Fe and Mn content in the solution.The addition of manganese in the culture medium can reduce the cadmium content of rice roots by 11.9-82.3%and the cadmium content of rice shoots by 11.6-85.0%;while the addition of iron in the culture medium can reduce the cadmium content of rice and roots shoots by 26-65%and 9-683%respectively.Meanwhile,under Fe and Cd treatments RE of CAL1,Os NRAMP5,Os NRAMP1,Os IRT1,and Os NAAT1 up-regulated in root,whereas expression level of Os HMA3 was down regulated.Similarly,under the Mn and Cd treatments expression of CAL1,Os NRAMP5,and Os NRAMP1 significantly increased in root.Thereby,it may be concluded that the Cd increases expression of CAL1,Os NRAMP5,Os NRAMP1,Os IRT1,and Os NAAT1 but decreases Os HMA3 expression in rice root and shoot,which resulted in increased Cd uptake in hydroponically grown rice.Innovation points of this research1.It is found that long-term use of chlorine-containing fertilizers significantly increases the Cd concentration in rice,while sulfate fertilizers have no significant effect on Cd in rice.The reason is that the former can promote the migration of Cd from soil to rice.2.It is found that planting green manure can significantly increase the cadmium content in rice,which provides a strong basis for correcting the wrong practice of cadmium-contaminated soil fallow-planting green manure.3.The expression levels of cadmium-related genes in rice under cadmium pollution conditions and their relationship with iron and manganese nutrition were ascertained.