Rice Cadmium Uptake By The Regional Model And Its Regulation

With the industrial development and widespread application of agricultural chemicals,heavy metals pollution in agricultural soils has attracted extensive attention, because of theirnon-biodegradability and persistence. Among them, cadmium(Cd)was considered as one of thepublic health hazard substances due to high mobility and high-toxic. Rice is the world's secondlargest, Chinese biggest food crop, and also is one of the most easily uptake and accumulationof Cd in staple food crops. Some surveys found that cadmium pollution was very serious inChinese farmland. Therefore, how to predict and regulate rice Cd accumulation for protectingsoil environmental quality and food safety is great significance. In this study, a large number ofpairs rice and soil samples of the typical red soil region were used in establishing the rice Cduptake regional prediction model, which was based on soil chemical properties and soil Cdform. And through the rice hydroponic and soil culture experiment to research the regulation ofrice Cd uptake. The main research results are as follows:(1)The analysis about106pairs soil and rice samples of typical red soil region of JiangxiProvince Yujiang showed that,22.6%soil samples Cd concentration was higher than thesecondary standard of Chinese soil environmental quality standard, and44.3%of the ricesamples Cd higher than Chinese food contaminants limited the Cd concentration of the standardrequirements. Soil samples pH is relatively low (4.45-5.80), and Cd activity and migrationability is higher in such soil, which may be the reasons about higher rate of rice Cd exceeded.The correlation analysis of soil samples and rice samples showed that, the concentration ofbioavailability Cd was very significantly(p<0.01)correlated with total soil Cd concentration,DOC and pH, the correlation coefficients were0.719,0.487and-0.303. The correlation amongCd concentration of rice with total soil Cd concentration, bioavailability Cd concentration andDOC was very significant(p<0.01)positive, the correlation coefficient were0.466,0.782and0.458,and the correlation with the SOM and pH was significantly(p<0.05)negative. Throughregression statistics analyzing about the total Cd concentration, bioavailability of Cdconcentration and each soil variable properties on the Cd concentration in rice, to establish arice Cd uptake prediction model of the typical red soil region. The linear equations R²adjbetween observed values and fitted values with the model established by the bioavailability ofCd concentration was0.847, and the linear equations R²adjbetween observed values and fittedvalues with the model established by the total soil Cd concentration was0.807, indicating thatthe bioavailability of Cd concentration is more important than the total soil Cd concentration onthe rice Cd accumulation.(2)Cadmium stress(5.0μmol L^-1)caused a significant inhibition of the rice seedlingsgrowth, the biomass of rice seedling without applying amino acids decreased by17.80%. Glutamate(Glu)and glycine(Gly)at three application rates did not influence rice plant biomassin comparison to the only Cd treatment, but25μmol L^-1cysteine(Cys)treatment reached thecontrol treatment(CK)level. Glutamate (Glu)reduced the accumulation of Cd concentrationof rice seedlings, especially in the high concentration addition of100μmol L^-1, theconcentration of Cd in the stems and leaves of rice seedlings decreased by23.36%and30.15%.The treatment of Gly and Cys failed to reduce the accumulation Cd of rice seedlings, even theconcentration of Cd in rice seedlings increased significantly under Cys treatment. Exogenousamino acids restricted Cd of transferring from roots to stems of the rice seedling, and increasedthe proportion of Cd in cell wall fractions of rice seedling roots, reduced the proportion of Cd inthe organelle fractions. All of the three amino acids played a role in decreasing lipidperoxidation, increasing catalase(CAT), superoxide dismutase(SOD)activities and glutathione(GSH)concentration.(3)By the TEM, XRD and FTIR-PAS technology on the straw biochar characterizationresults showed that, the biochar was fragmented superposition of layers of porous, andgenerated carbonate composition. Biochar has good adsorption performance of Cd²⁺, and theadsorption ability increased with pH enhanced. Langumir equation can be well described theCd²⁺adsorption behavior by biochar surface in under the conditions of pH4.5and5.5, thefitting correlation coefficients were0.998and0.997. Biochar significantly increased the pottedsoil solution pH and DOC content, and the increased rate correspondingly with the biocharadditive amount. Biochar inhibited the bioavailability of Cd concentration, compared with CK,bioavailability of Cd in potted soil under0.5%,1%and2%biochar treatments were reduced by5.32%,18.17%and46.94%, and promoted soil exchangeable Cd conversion to the restore stateand oxidisable steady-state. Biochar had a very significant role in promoting growth on the ricewhich was growing in the Cd contaminated soil. The rice plant height, rice grain yield andwhole rice plant biomass had a large increase at harvest. Rice grain yield and whole plantbiomass increased to about2times contrast to CK treatment at2%biochar treatment. Biocharsignificantly reduced the Cd concentration of potted rice grain. The Cd concentration of ricegrain decreased97.34%,66.11%and58.24%under0.5%,1%and2%biochar treatments, andthe rice grain in the0.5%,1%treatments to reach the edible standard. Biochar had a goodcontrol effect on rice Cd uptake, not only reduced the concentration of Cd in rice grains, butalso promoted the growth of rice biomass.(4)The surface of Nano-hydroxyapatite(nano-HAP)on the adsorption behavior of Cd²⁺was also can be described by Langumir equation, and Cd²⁺adsorption capacity of nano-HAPwas higher than the biochar. nano-HAP significantly improved soil solution pH, but lesseffected on soil solution DOC. nano-HAP significantly inhibited Cd bioavailability. Thebioavailability of Cd concentration in the potted soil decreased by63.21%,80.62%and92.32%under the0.5%,1%and2%nano-HAP treatment. And nano-HAP promoted the exchangeableform Cd to transformation of to a more stable form. nano-HAP also had some role in promoting potted rice growth under Cd pollution, but the effect was not obvious. Nano-HAP significantlyreduced the potted rice grain Cd content, respectively by85.92%,89.47%and94.68%under0.5%,1%and2%nano-HAP treatment, all rice grain meeted the standards prescribed andcan be eaten. Nano-HAP had a good regulation of rice Cd uptake, and not only significantlyreduced the bioavailability of Cd concentration, but also significantly reduced the Cdconcentration of rice grain.