Cd Concentrations In Brown Rice Research Articles

Effect of RM-based-passivator for the remediation of two kinds of Cd polluted paddy soils and mechanism of Cd(II) adsorption

ABSTRACT This study aimed to investigate the effects of red mud-based-passivator (RM-based-passivator) on rice yield, cadmium (Cd) in brown rice, pH and available Cd in Cd-polluted soil by pot experiments, and to explore the adsorption mechanism of the passivator by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis. The results showed that this passivator obviously improved the pH, reduced the available Cd in soil and the Cd content in brown rice in Changsha Cd polluted soil (CS soil), while had little effect on Hengyang Cd polluted soil (HY soil). Compared with the control, the soil pH increased in the range from 0.31 to 1.37, the available Cd in soil decreased in the range from 13.25% to 52.34%, and the total Cd in brown rice decreased in the range from 46.44% to 84.98% in CS soil. Considering the impacts of RM-based-passivator on the growth of rice, the Cd content in brown rice, and the pH and available Cd in soil, 0.10–0.30% (w/w) of the passivator is recommended to apply in CS soil but not in HY soil. Based on the analysis of SEM, EDX, FTIR and XRD, the mechanism of Cd(II) adsorption by RM-based-passivator included physical adsorption, surface complexation and ion exchange. The present results indicated that the appropriate addition of RM-based-passivator could be an effective strategy for the remediation of acidic Cd-polluted soils.

Effect of Conditioning Agent Combined with Flooding Measures on Absorption and Accumulation of Cadmium in Rice

In order to evaluate the effects and mechanisms of flooding measures, soil conditioner, silicon mineral fertilizer and sprayed foliar fertilizer, gypsum powder, and their multiple treatments for reducing Cd accumulation in rice grown in Cd-contaminated soil. A plot experiment was conducted in three different Cd-contaminated soils. The results showed that flooding measures, a single application of conditioning agents, and combined application and flooding treatment can reduce soil-available Cd and the Cd content in various organs of rice with 6.58%-30.01% reduction in soil available-Cd and 12.64%-68.68% reduction in Cd content in brown rice, respectively. The Cd reduction decreased in the following order:comprehensive treatment (T6) > basic application of gypsum powder (T5) > base Xiangrunbang state soil conditioner (T3) > mineral silicon fertilizer and spray foliar fertilizer (T4) > flood treatment (T2). In addition, the average value of the reduction effect of the Cd content in brown rice was calculated. The five treatments in the experiment reduced the enrichment of various parts of the rice, which is a main reason for the decrease in Cd content in the brown rice. According to the field plot test, the combined application of the basic conditioning agent, mineral silicon fertilizer, and sprayed foliar fertilizer, and gypsum powder and flooding measures can be used as an effective method for Cd pollution control in Cd-contaminated cultivated rice.

Hybrid ash/biochar biocomposites as soil amendments for the alleviation of cadmium accumulation by Oryza sativa L. in a contaminated paddy field

A novel ash/biochar (A/B) biocomposite composed of 90% biomass bottom ash from agroforestry biomass direct-fired power plants, 5% animal-derived biochar from carcass pyrolysis, and 5% bentonite as an adhesive was amended in cadmium (Cd)-polluted paddy soil to alleviate cadmium accumulation by Oryza sativa L. Ash increased the soil pH and contributed exogenous available silicon. Biochar with high Ca/P components played an important role in soil cadmium immobilization. A 1-year field experiment with consecutive rice growing seasons (early and late rice) was conducted in Xiangtan, China, to examine the effects of A/B amendment in Cd-contaminated paddy soil. The A/B biocomposite was amended into soil through one-time addition at three application rates (1, 5, and 10 kg/m2). When A/B amendment was ≥5 kg/m2, the soil pH increased from 4.11 to more than 6. The available silicon content in the soil even increased by 22.9 times. For early rice soil, the CaCl2-extractable Cd(II) and toxicity characteristic leaching procedure (TCLP)-extractable Cd(II) decreased by 77.9%–96.1% and 52.4%–70.7%, respectively. A/B remarkably reduced Cd accumulation in rice organs, and this observation was related to A/B treatment rates. Ash and biochar contributed to the inhibition of Cd accumulation in rice organs and Cd translocation from roots to stems. The Cd concentrations in brown rice decreased to 0.11 and 0.12 mg/kg in early and late rice, respectively, and these values were lower than the national food safety standard limit value of China (0.2 mg/kg).

Genetic properties of cadmium translocation from straw to brown rice in low-grain cadmium rice (Oryza sativa L.) line

Breeding the rice cultivar with high cadmium (Cd) accumulation in straw but with low Cd in brown rice using marker-assisted selection (MAS) based on quantitative trait loci (QTL) is meaningful for phytoremediation as well as safety in production. A restorer rice line, YaHui2816, steadily showed low Cd translocation from straw to brown rice and carried alleles for reducing Cd concentration in brown rice (BRCdC). In this study, one F2 population (C268A/YaHui2816) was used to identify the QTLs for BRCdC in 2016, and other two different F2 populations (Lu98A/YaHui2816 and 5406A/YaHui2816) were used to furtherly validate the QTLs in 2017. Furthermore, a pot experiment was conducted to investigate the relative expression of predicted genes in the regions of these QTLs for BRCdC. Here 4 QTLs for BRCdC were identified, among which, 2 novel QTLs (qBRCdC-9 and qBRCdC-12) were identified on chromosomes 9 and 12 in rice. The YaHui2816 alleles in the QTLs qBRCdC-9 and qBRCdC-12 could effectively reduce BRCdC under different genetic backgrounds. Importantly, the QTL qBRCdC-12 was simultaneously associated with the Cd translocation from shoot to brown rice (T-s-b), genetically explaining that the low T-s-b of the YaHui2816 resulted in its low BRCdC. The interval length of the QTL qBRCdC-12 was only narrowed to 0.28 cM, making it possible to develop molecular markers and excavate genes for reducing BRCdC. It is worth noting that genes existed in these QTL regions have not been reported for regulating the Cd translocation in rice. 6 candidate genes (OS05G0198400, OS05G0178300, OS09G0544400, OS12G0161100, OS12G0162100 and OS12G0165200) up-regulated expressed in nodeⅡof the YaHui2816 in response to Cd treatment, and encoded ZRT/IRT-like protein (ZIP) 4, the protein similar to glutathione transferase (GSTs) 16, heat shock protein Hsp20 domain containing protein, MAP kinase-like protein and Cd tolerant protein 5, respectively.

Phosphate addition diminishes the efficacy of wollastonite in decreasing Cd uptake by rice (Oryza sativa L.) in paddy soil

Cadmium (Cd) contamination in paddy soils poses food security risks and public health concerns. Exploring effective strategies to reduce rice grain Cd is an urgent need. In this study, field plot experiments were conducted to evaluate the effects of wollastonite application with or without phosphate (P) addition on Cd accumulation in rice (Oryza sativa L.). Co-application of P and wollastonite showed greater efficiency than wollastonite amendments alone in raising soil pH and CEC and decreasing soil Cd availability. Cd concentration in brown rice was decreased by 71% under the wollastonite treatment alone, but was decreased by only 29–39% when wollastonite was coupled with different P amendments. This seeming contradiction could be ascribed to the dramatic decline in the phytoavailability of manganese (Mn) and the increase in molar ratio of iron (Fe) to Mn (Fe/Mn) in Fe plaques on root surfaces in the presence of P additions. Significant negative correlations between Mn and Cd in rice plants and positive correlations between Fe/Mn in Fe plaque and Cd in rice plants indicated that P-induced soil Mn deficiency and reduced Mn in Fe plaque impeded the alleviation of Cd accumulation in rice. Application of wollastonite in Si-deficient paddy soils was effective in reducing rice Cd accumulation while boosting rice yield, but co-application of P and wollastonite was counterproductive and should be avoided. This work emphasized that a better understanding of the relationships between Cd and related mineral nutrient uptake would be helpful in developing more efficient measures to reduce rice grain Cd.

Cadmium accumulation and bioavailability in paddy soil under different water regimes for different growth stages of rice (Oryza sativa L.)

Cadmium (Cd) is a ubiquitous environmental pollutant, and rice (Oryza sativa L.) is the main staple food in China. Water regimes are promising, controllable, and environment-friendly agricultural measures for remediation Cd contaminated soil. The optimum water regime for ensuring high rice yield with low Cd contents in brown rice was investigated. A pot experiment was conducted to study the effects of Cd migration and accumulation from paddy soil to rice plants under four water regimes with three growth stages of two rice cultivars, ‘Xiangwanxian 12’ (X12) and ‘Weiyou 46’ (W46) grown in a polluted soil with 5 mg kg−1 of Cd. The relationship between Cd accumulation amounts in rice plant and soil Eh was also investigated. The four regimes were moisture throughout growth (M), moisture before the filling stage and flooding after filling (M-F), flooding before filling and moisture after filling (F-M), and continual flooding (F). Water regimes effectively reduced Cd accumulation in rice at the three growth stages, whereas the filling stage was suggested to be as the key stage for interventions to prevent Cd transport and accumulation. Compared with M, the M-F, F-M, and F regimes significantly reduced Cd contents of rice tissues (root, stem, husk, and brown rice) at the maturity stage. Under the M, F-M, M-F, and F regimes, Cd contents were 2.17, 2.10, 0.21, 0.06 mg kg−1 in X12 brown rice and 3.27, 0.47, 0.19, 0.10 mg kg−1 in W46 brown rice, respectively. Importantly, Cd contents of brown rice of X12 (0.06 mg kg−1 under regime F) and W46 (0.19 mg kg−1 under regime M-F and 0.10 mg kg−1 under regime F) did not exceed China’s food safety standard of 0.20 mg kg−1 (GB 2762–2017). Moreover, there were significant positive exponential relationships between soil Eh and Cd accumulation amounts in belowground and aboveground parts of rice. The M-F regime (W46) and F regime (X12) could ensure high rice yield with low Cd contents in brown rice and could be recommended as the irrigation management in rice production. Simultaneously, keeping soil Eh under 50 mV is also necessary after the rice filling stage.

Changes of non-protein thiols in root and organic acids in xylem sap involved in cadmium translocation of cadmium-safe rice line (Oryza Sative L.)

The selection and breeding of low grain-cadmium (Cd)-accumulating rices is a promising approach for reducing the Cd concentration in grains. A cadmium-safe rice line designated D62B (Oryza Sative L.) accumulated a low Cd concentration in brown rice for safe consumption (< 0.2 mg kg−1). D62B was a great potential breeding material with a weaker translocation capacity of Cd to shoot compared with common rice lines. A prior understanding of the Cd translocation mechanisms in D62B offered theoretical basis for breeding new low-Cd-accumulating rice cultivars in the future. A pot experiment was conducted to investigate the changes of non-protein thiols in shoot and root of D62B in comparison with a common rice line (Luhui17), and then the relationship between the Cd translocation via xylem and organic acids in xylem sap of two rice lines was explored by a hydroponic experiment. D62B showed lower Cd translocated to shoot in comparison with Luhui17. The translocation factor (TF) of D62B varied from 0.11 to 0.15. Cd exposure promoted the synthesis of non-protein thiols in two rice lines, particularly in roots. Syntheses of glutathione (GSH) and phytochelatins (PCs) in root of D62B were greater than those of Luhui17. Cd concentration in xylem sap of D62B was significant positively correlated with the malic acid, citric acid and tartaric acid concentrations. The citric acid and tartaric acid concentrations in xylem sap of D62B were significantly lower than those of Luhui17. There was no significant difference for malic acid between two rice lines. More GSH and PCs in root of D62B was beneficial to Cd retention in root. Furthermore, the involvement of lower citric acid and tartaric acid in Cd translocated in xylem sap of D62B resulted in lower Cd accumulation in shoot.

Producing cadmium-free Indica rice by overexpressing OsHMA3

BackgroundConsiderable proportions of rice grains produced in some areas in southern China contain high concentrations of cadmium (Cd), leading to unsafe levels of dietary Cd intake. Cultivars of Indica rice, widely grown in southern China, are particularly prone to high Cd accumulation in the grain. Effective methods are needed to decrease Cd accumulation in Indica rice. MethodsOsHMA3, encoding a tonoplast Cd transporter, was overexpressed in an elite Indica rice cultivar (Zhongjiazao 17) driven by CaMV 35S promoter. The effects on Cd translocation, accumulation and tolerance, as well as on the agronomic traits and micronutrient concentrations were evaluated. ResultsOsHMA3 overexpression markedly decreased Cd translocation from roots to shoots and increased Cd tolerance. OsHMA3 overexpression decreased Cd concentrations in brown rice by 94–98%, to levels just above the detection limit, when rice plants were grown in two Cd-contaminated paddy soils. OsHMA3 overexpression generally had no significant effect on grain yield and the concentrations of the essential micronutrients including zinc, iron, copper and manganese in field trials. ConclusionOverexpression of OsHMA3 is a highly effective method to reduce Cd accumulation in Indica rice, producing rice grains that were almost Cd free with little effect on grain yield or essential micronutrient concentrations.

Inhibition of Cd accumulation in grains of wheat and rice under rotation mode using composite silicate amendment.

The accumulation of heavy metals in soils and crops jeopardizes human health, and thus remedying soil and ensuring food safety have attracted wide concern. In this study, composite silicate was employed as an amendment to inhibit cadmium (Cd) accumulation in the grains of wheat and rice in an upland/paddy rotation mode in field-scale remediation. The composite silicate amendment (CSA) at a dosage of 0.2–0.8% decreased the Cd concentration in wheat grains in the first growing season of upland mode by 7.5–58.3% compared with CK, and decreased the Cd concentration in brown rice by 38.7–58.1% in the second season of paddy mode. The minimum values satisfy the Chinese National and International Standards. The results confirmed the inhibitory effect of CSA on the accumulation of Cd in crop grains. CSA increased the soil pH obviously and enhanced the sorption of Cd on soil particles by 14.6–56.2%, and declined the DTPA- and HCl-extractable Cd concentrations in the soil by 16.2–49.5% and 23.8–75.6%, respectively. Furthermore, CSA decreased the exchangeable Cd fraction by 21.5–41.6% in the sequential extraction. The immobilization effect was retained in both growing seasons in terms of Cd concentration in the crop grains and extractable Cd concentration in the soil. CSA had a negligible effect on the normal growth of wheat and rice and the available Zn and Cu concentration in the soil, indicating its environmental friendliness. Considering its low cost and abundant reserves, CSA can be recommended as an immobilization amendment for Cd-polluted paddy soil in wheat/rice rotation mode.

Cadmium in rice grains from a field trial in relation to model parameters of Cd-toxicity and -absorption in rice seedlings

Selecting rice varieties that absorb less Cd from soil will reduce human health risks posed by Cd through rice consumption. Nine rice cultivars that are commonly grown in Taiwan were used for investigating genotypic differences in Cd tolerance and absorption. Hydroponic testing with Cd treatments of 5, 10, and 50 μM CdCl2 for 7-day exposure was conducted for the cultivars. The reductions in plant growth by Cd treatments were fitted to a dose-response curve; the modeling parameters, that is, the effective Cd concentration resulting in 50% reduction (EC50), were obtained. The Cd concentrations in plant were expressed by a Michaelis–Menten kinetic model and the uptake rate parameters (M/k) were obtained. A field experiment was also conducted in farmland with Cd ~0.2 mg kg−1 in soil. For the rice cultivars used in hydroponics, Cd distributions and physiological traits (CAT, H2O2, and MDA) in seedlings were related to their tolerances to Cd toxicity. Modeling parameters, EC50 and M/k, correspond to the Cd concentrations in rice plant. In the field experiment, the Cd concentrations in brown rice of the indica cultivars (i.e., TCS10, TCS17, and TNGS22) were 0.6 mg kg−1; these were significantly higher than those of the japonica cultivars (i.e. TY3, TK9, TNG71, KH145, TKW1, and TKW3). By contrast, the three cultivars, KH145, TKW1, and TKW3, whose Cd concentrations in brown rice were lower than 0.3 mg kg−1 were considered safe relative to the permissible level of 0.4 mg kg−1. In addition, for the used cultivars, Cd concentrations in brown rice were well expressed (i.e., r2 = 0.95) as a function of EC50, M/k, and MDA by using multiple regression. Newly bred cultivars could be screened rapidly with hydroponic testing to predict their Cd concentrations in brown rice when grown in the field.

Prediction of cadmium concentration in brown rice before harvest by hyperspectral remote sensing.

Cadmium (Cd) contaminated rice has become a global food security issue. Hyperspectral remote sensing can do rapid and nondestructive monitoring of environmental stress in plant. To realize the nondestructive detection of Cd in brown rice before harvest, the leaf spectral reflectance of rice exposed to six different levels of Cd stress was measured during the whole life stages. In addition, the dry weight of rice grain and Cd concentrations in brown rice were measured after harvest. The impact of Cd stress on the quantity and the quality of rice grain and on the leaf reflectance of rice was analyzed, and hyperspectral estimation models for predicting the Cd content in brown rice during three growth stages were established. The results showed that rice plants can impact the quality of the brown rice seriously, even if the impact on the quantity was not significant. All the established models had the capability to estimate Cd concentrations in brown rice (R2 > 0.598), and the best performance model, with the R2 value of 0.873, was use first derivative spectrum of booting stage as variable. It was concluded that the hyperspectral of rice leaves provides a new insight to predict Cd concentration in brown rice before harvest.

Decreasing cadmium uptake of rice (Oryza sativa L.) in the cadmium-contaminated paddy field through different cultivars coupling with appropriate soil amendments

In southern China, Cd-tainted rice produced in Cd-contaminated acidic paddy soils is a serious health concern. Thus, it is essential and urgent to remediate Cd-contaminated soils and reduce Cd accumulation in rice grains for food safety and human health. Four soil amendments (e.g., lime, biochar, soil conditioner, and seaweed organic fertilizer) combined with two rice cultivars (Yongyou17, YY-17; and Xiushui09, XS-09) with different Cd accumulation abilities were selected to evaluate the efficacy of safe utilization in a slightly moderately Cd-contaminated paddy soil. Results showed that soil amendments significantly increased soil pH and reduced Cd bioavailability compared with the control. Linear regression analysis showed that the decrease in Cd bioavailability was significantly and positively correlated with soil pH increase (P < 0.001). Soil amendments were efficient in reducing Cd uptake by rice root as well as translocation from root to aboveground plant parts. The Cd concentrations in brown rice of YY-17 and XS-09 were 0.34 and 0.22 mg kg−1 for control treatments, respectively, while the Cd concentrations of rice grain using were reduced by 45 to 88% and 55 to 88% soil amendments for two cultivars. Considering the costs and efficiency of soil amendments, the soil conditioner was the best amendment. In situ immobilization combined with low-Cd-accumulation rice cultivar is an effective approach for food safety in lightly moderately Cd-contaminated acidic paddy soils.

Accumulation of Heavy Metals in Different Rice Varieties

Field experiments were conducted on the heavy metal contents (Cd, Pb, Cr, inorganic As, and total Hg) of the 129 main cultivated rice varieties in southern China. We analyzed the effects of different varieties and types of rice on the absorption capacities of these heavy metals. The results showed that the Cd content in 35 brown rice of early rice was 0.35-0.60 mg·kg-1, exceeding the standard rate of 100%. The Pb content in brown rice was 0.08-0.30 mg·kg-1, exceeding the rate of 14.29%. The Cd content in 54 brown rice of medium rice was 0.03-0.45 mg·kg-1, exceeding the rate of 33.33%. The Cd content in 40 brown rice of late rice was 0.08-0.20 mg·kg-1, which did not exceed the national standard. Early, middle, and late rice all showed that the Cd content of three-line hybrid rice was higher than that of two-line hybrid rice, but the difference was not obvious. The contents of Cr and total Hg in brown rice of three-line hybrid rice in early rice were significantly higher than that of two-line hybrid rice. There was a significant positive correlation between Cd content in brown rice and Pb and total Hg content in medium rice, and there was a significant negative correlation between inorganic Cd content and inorganic As content, whereas there was no significant correlation between Cd and Cr content. In short, rice's absorption and accumulation of heavy metals is greatly affected by genetic background, species types, and heavy metal interactions.

Effects of Exogenous 5-Aminolevulinic Acid and 24-Epibrassinolide on Cd Accumulation in Rice from Cd-Contaminated Soil

High grain-Cd-accumulating rice variety Yongyou 9 was planted in Cd-contaminated farmland in Taizhou City, Zhejiang Province, China to study the effects of 5-aminolevulinic acid (ALA) and 24-epibrassinolide (EBR) on Cd accumulation in brown rice. Results showed that the exogenous ALA and EBR had no significant effects on agronomic traits, soil pH and total Cd content in soil, but had some effects on the available Cd content in soil, and significantly influenced the Cd accumulation in the different parts of rice. Results also showed that 100mg/L exogenous ALA significantly reduced the Cd accumulation in brown rice to blow the food safety standard (0.2mg/kg), and also significantly reduced the Cd contents in the roots and culm of rice. However, 200mg/L exogenous ALA treatment increased the Cd content in brown rice remarkably. In addition, 0.15mg/L EBR treatment increased Cd accumulation in roots, culm, leaves and brown rice notably, whereas 0.30mg/L exogenous EBR treatment reduced the Cd accumulation in brown rice properly, but it was not significant. Therefore, proper concentration of ALA can effectively reduce the Cd accumulation in brown rice, which can be used as an effective technical method for the safe production of rice in Cd polluted farmland.

Effectiveness of simultaneous applications of lime and zinc/iron foliar sprays to minimize cadmium accumulation in rice

Due to the large area of Cd-contaminated paddy soils worldwide, low-cost measures to reduce the accumulation of Cd in rice plant are necessary. A field experiment was therefore conducted to investigate the reducing effect of lime combined with foliar applications of Zn (ZnSO4) or Fe (EDTA·Na2Fe) on Cd concentrations in brown rice on a Cd-contaminated paddy soil. The results indicated that liming alone or in combination with foliar sprays of Zn or Fe increased the soil pH by 0.27–0.63 units. However, limited effects of lime or lime combined with foliar applications of Zn/Fe on soil DTPA-extractable Cd, rice grain and rice straw biomass were observed. Liming alone significantly reduced the Cd concentration in brown rice and rice straw by 31.8% and 42.3%, respectively. The Cd concentrations in brown rice decreased by 25.5% and 65.4% and in rice straw by 53.0% and 68.1% after liming combined with foliar applications of Fe and Zn, respectively. In contrast, liming combined with foliar spraying of Fe significantly increased the transfer ratio of Cd from the rice straw to the grain. As a low-cost technique, lime application combined with foliar application of ZnSO4 could be recommended for the remediation of Cd-contaminated paddy soils.

Evaluation of Calcium Oxide of Quicklime and Si–Ca–Mg Fertilizer for Remediation of Cd Uptake in Rice Plants and Cd Mobilization in Two Typical Cd-Polluted Paddy Soils

Lime and Si fertilizer are effective amendments for alleviating Cd accumulation in crops. In this study, two Cd-polluted typical soils from different regions in China were sampled to conduct a pot experiment. The effects of two soil amendments [calcium oxide of quicklime (SH) and Si–Ca–Mg fertilizer (GF)] on the distribution of Cd fractions in soil with and without rice-planting treatment and on Cd uptake and accumulation in rice were investigated. The results showed that SH and GF application significantly reduced Cd accumulation in rice in YSS and GSS, and that the maximum Cd reduction in GSS reached 319 μg pot−1 with SH treatment. SH and GF significantly decreased and increased, respectively, the proportions of Acid-Cd and Res-Cd in the soil. Rice-planting treatment activated Res-Cd compared with no rice-planting treatment, and SH and GF restrained the remobilization process. Significant positive correlations were found between Res-Cd remobilization rates in soil and Cd content in brown rice. Multiple regression revealed that applying GF at dosages of 1.296 g kg−1 and 1.246 g kg−1 in YCS and GSS, respectively, was an ideal method to control soil acidity. This study highlighted the view that Res-Cd remobilization provoked by rice plays a considerable role in influencing Cd bioavailability in the soil, that soil type should be considered as a factor when applying soil amendments to contaminated soils, and that soil amendment dosages should vary according to soil type.

Foliar application of Zn can reduce Cd concentrations in rice (Oryza sativa L.) under field conditions.

Cadmium (Cd) pollution in rice and its transfer to food chain are cause of global concern. Application of zinc (Zn) can reduce Cd uptake by plants, as both these metals are generally antagonistic in soil-plant systems. In a field experiment on Cd-contaminated acid soil, we investigated the effectiveness of foliar application of Zn in minimizing Cd accumulation and its effect on the content of mineral nutrient elements in rice. The treatment was done at an early grain filling stag using 0.3 and 0.5% w/v ZnSO4·7H2O solution. The spray did not affect the grain yield of rice but decreased the Cd concentration in the root, straw, husk, and brown rice to some extent and increased the Zn concentration. Foliar application of 0.5% ZnSO4 resulted in maximum Zn concentration and minimum Cd concentration in brown rice. However, the concentrations of P, K, Ca, Mg, Cu, and Mn in brown rice were not affected. The correlation between Cd and Zn concentrations in brown rice, husk, and root was significantly negative, and that between Cd and Mn concentrations in brown rice was significantly positive. The inhibition of Cd uptake resulted in a decrease in its concentration in brown rice after the treatments. Thus, the foliar application of a suitable concentration of Zn at the early grain filling stage could effectively minimize the Cd concentration while enhancing the Zn concentration in brown rice on Cd-contaminated acid soil.

Biochar reduced soil extractable Cd but increased its accumulation in rice (Oryza sativa L.) cultivated on contaminated soils

This study focused on the effects and mechanisms of biochar amendment to Cd-contaminated soil on the uptake and translocation of Cd by rice under flooding conditions. Pot and batch experiments were conducted using Cd-contaminated soil collected from a field near an ore mining area and a cultivar of Oryza sativa ssp. indica. Biochar derived from rice straw under anaerobic conditions at 500 °C for 2 h was mixed with the soil at the rate of 0, 2.5, and 5%. The application of 5% biochar reduced CaCl2-extractable soil Cd by 34% but increased Cd concentration in brown rice by 451%. Biochar amendment decreased water-soluble Fe2+ in soils and formation of Fe plaques on roots and weakened the Fe2+-Cd2+ competition at adsorption sites on the root surface. Biochar increased water-soluble Cd in the soil and consequently Cd uptake by rice roots by releasing water-soluble Cl−. Biochar application also reduced the proportion of cell wall-bound Cd in the root, which caused easier Cd translocation from the cortex to the stele in the root and up to the shoot. Rice straw biochar (with high concentration of water-soluble Cl−) reduced CaCl2-extractable soil Cd but increased Cd concentration in rice under flooding condition.

Identification of QTLs associated with cadmium concentration in rice grains

Cadmium (Cd) contamination in rice has been a hot topic of research because of its potential risk to human health. In this study, a double haploid (DH) population derived from Zhongjiazao 17 (YK17) (an early-season indica cultivar)×D50 (a tropical japonica cultivar) was used to identify quantitative trait loci (QTLs) associated with Cd concentration in brown rice (CCBR) and Cd concentration in milled rice (CCMR). Continuous and wide variation for CCBR and CCMR were observed among the DH population. Correlation analysis revealed a positive and highly significant correlation between the two traits. A total of 18 QTLs for CCBR and 14 QTLs for CCMR were identified in five different pot and field trials. Two pairs of QTLs for CCBR (qCCBR2-1 and qCCBR2-2, qCCBR9-1 and qCCBR9-2) and one pair of QTLs for CCMR (qCCMR5-1 and qCCMR5-2) were detected in multiple trials. The alleles increasing CCBR at the qCCBR2-1/qCCBR2-2 and qCCBR9-1/qCCBR9-2 QTLs were contributed by YK17 and D50, respectively, whereas the D50 allele at the qCCMR5-1/qCCMR5-2 QTLs increased CCMR. Eight pairs of QTLs for CCBR and CCMR, qCCBR2-2 and qCCMR2-2, qCCBR3 and qCCMR3, qCCBR4-2 and qCCMR4-1, qCCBR4-3 and qCCMR4-2, qCCBR4-4 and qCCMR4-3, qCCBR5 and qCCMR5-2, qCCBR7 and qCCMR7, and qCCBR11-1 and qCCMR11-2, co-localized on chromosomes 2, 3, 4, 5, 7, and 11, respectively. For all of these QTL pairs, except qCCBR5/qCCMR5-2, the additive effects came from YK17. In addition, four CCMR QTLs showing significant additive×environment interaction and two pairs of CCMR QTLs with bi-allelic epistatic interactions were identified. The results of this study could facilitate marker-assisted selection of breeding rice varieties with low Cd accumulation in grain.

Effects of a Tribasic Amendment on Cadmium and Arsenic Accumulation and Translocation in Rice in a Field Experiment

An in-situ paddy field experiment was carried out to study the influence of a tribasic amendment (QFJ, hydroxyapatite+zeolite+biochar) on Cd and As accumulation and translocation in rice grown in soil contaminated with cadmium and arsenic, with the concentrations of soil Cd and As being 3.58 mg·kg-1 and 124.79 mg·kg-1, respectively. The results showed that, after application of QFJ, the pH, CEC, and OM contents of the rice rhizosphere soil tended to increase. The exchangeable concentrations of Cd and As were reduced from 0.37 mg·kg-1 and 0.07 mg·kg-1 to 0.12 mg·kg-1 and 0.04 mg·kg-1, respectively. The concentrations of Cd and As in rice tissues decreased after in-situ restoration. When 9.00 t·hm-2 of QFJ was applied, the Cd concentration in brown rice was reduced from 0.46 to 0.18 mg·kg-1, and that of inorganic As was reduced from 0.25 to 0.16 mg·kg-1, both lower than 0.2 mg·kg-1, meeting the requirement set by the National Food Standards (GB 2762-2012). QFJ application decreased the Cd and As bioaccumulation capacity of the roots and decreased the rice plant's capacity of Cd translocation quantity from the underground parts to the aerial parts; at same time, the Cd transferring capacity of the roots and the As transferring capacity in straw and husk were also decreased.