Intercropping with herbs minimizes cadmium availability through altering physicochemical dynamics and metabolite profiles in wheat rhizosphere

For the past few years, the production of safe crops in Cd-contaminated soil has attracted more and more attention, and the intercropping of wheat and herbaceous plants has gradually become an effective way. However, how the physicochemical and metabolic processes because of the intercropping change Cd availability are still unclear. In this study, we studied the influence of changes in soil physicochemical properties induced by intercropping of wheat with different herbs on soil Cd availability of Cd. Meanwhile, we innovatively studied the effect of intercropping on rhizosphere metabolites and evaluated the impact on Cd transfer. Results showed that the highest wheat biomass was presented in the intercropping system with the Cichorium intybus L. (W4) and Aus hypochondriacus L. (W5) increasing by 57.66% and 54.05% individually, compared with monocropping, while W1, W2, and W3 increasing slightly. Further, the Cd accumulation in wheat grains under W4 and W5 treatment decreased by 44.95% and 43.12%, respectively. Structural equation model confirmed that the increased pH, CEC contributed to the decreased Cd availability in soil, as well the changed metabolic profiles in wheat rhizosphere after intercropping. Specially, up-regulation of fatty acid metabolism allowed wheat plants to maintain a normal intracellular environment under stress conditions. Similarly, up-regulation of saccharide and amino acid metabolism induced the accumulation of sugars and proteins, which positively increased wheat biomass and Cd-binding proteins, thus inhibiting the migration of soil Cd into wheat tissue. Collectively, this study provided reasonable insights towards understanding the metabolic mechanisms how intercropping altered Cd availability.     

Effect of humic acid amendment on cadmium bioavailability and accumulation by pak choi (Brassica rapa ssp. chinensis L.) to alleviate dietary toxicity risk

Cadmium (Cd) contamination in soil and its movement into food chain through vegetable dietary poses a risk to human health. A pot experiment was conducted to investigate the effect of humic acid (HA) and two cultivars of Brassica rapa ssp. chinensis L. (pak choi) with differing Cd accumulation abilities on Cd accumulation in different Cd contaminated Ferralsol, Histosol and Luvisol soils. The results showed that HA significantly increased soil pH and cation exchange capacity in Ferralsol (acidic) and Histosol (neutral) soils. HA was more effective in Ferralsol and Histosol soil in reducing bioavailable Cd and its accumulation in both cultivars. Low and high Cd accumulating cultivars combined with HA effectively reduced shoot Cd concentration by 7–34% and 19–35% in Histosol soil, whereas 22–34% and 11–26% in Ferralsol soil, respectively. However, no such reduction was observed for Cd accumulation and bioavailability in Cd-contaminated Luvisol (alkaline) soil. Application of HA enhanced shoot dry biomass in both cultivars grown in Histosol and Ferralsol soils. Therefore, the HA amendment combination with low Cd accumulating cultivars of pak choi could be an effective method for phytostabilization and reduce health risks associated with consuming this vegetable grown in Cd-contaminated acidic and neutral pH soils.     

羟基磷灰石–植物联合修复对Cu/Cd污染植物根际 土壤微生物群落的影响

针对江西贵溪Cu、Cd重金属污染土壤,通过田间试验,比较无机生物材料羟基磷灰石及3种植物(海州香薷、巨菌草、伴矿景天)与羟基磷灰石联合修复对土壤总Cu、Cd的吸收及对活性Cu、Cd的钝化吸收能力差异。采用磷脂脂肪酸(PLFA)分析法,比较不同修复模式对土壤微生物群落结构的影响,以评估土壤微生态环境对不同修复措施的响应。研究结果表明:羟基磷灰石的施加可显著提高土壤pH,并有效钝化土壤活性Cu、Cd含量,但对土壤总Cu、Cd的含量影响较小。植物与羟基磷灰石的联合修复在显著降低土壤活性Cu、Cd(P0.05)的同时,减少了植物根际土壤总Cu、Cd的含量(P0.05)。不同修复措施对土壤微生物群落组成影响差异明显。单独施加羟基磷灰石与土壤真菌群落呈显著正相关,使土壤真菌生物量提高,从而引起真菌/细菌(F/B)的升高。植物与羟基磷灰石的联合修复可有效缓解土壤真菌化的趋势,其中巨菌草与羟基磷灰石的联合修复可有效提高土壤革兰氏阳性、革兰氏阴性细菌生物量及多样性,降低F/B值,从而降低土壤真菌病害的风险。不同植物根系活性代谢引起有机质的积累促进植物与羟基磷灰石处理中根际有机碳含量显著提高。聚类增强树(Aggregated boosted tree,ABT)分析结果表明:不同修复模式是影响土壤微生物群落的重要因素,其次土壤pH和Cu的含量及活性也是改变重金属污染区域微生物群落的因子。该研究从微生物群落结构角度解释了植物与羟基磷灰石联合修复对土壤微生态体系的作用,为开展Cu、Cd等重金属污染地植物与无机生物材料的联合修复方式的筛选及实施提供可靠的理论依据。     

Effect of soil cadmium concentration on three Chilean durum wheat cultivars in four environments

Durum wheat (Triticum turgidum L. var durum) is a species that accumulates cadmium (Cd). Durum wheat cultivars differ in their absorption ability of Cd; therefore, identifying and selecting genetic material with low Cd accumulation reduces human exposure to this toxic element. In the present study, Cd concentration was evaluated in three Chilean durum wheat cultivars (Llareta-INIA, Corcolén-INIA, and Lleuque-INIA) grown in four Chilean locations with varying concentrations of Cd in soils. The objective of this study was to evaluate the response of these durum wheat cultivars to different doses of cadmium in terms of grain yield; Cd concentration in different plant tissues (grain, straw, roots); soil Cd concentration was also evaluated. Results show that grain yield was not affected by soil Cd; differences in Cd concentration in plant tissues were generally associated with location, cultivar, and soil Cd concentration. Grain Cd concentration in all three cultivars was classified in the low accumulation category for this metal; ‘Lleuque-INIA’ noted as having a very low accumulation.     

外源锌对水稻植株镉的累积差异分析

通过水稻威优46盆栽种植试验,研究了外源Zn施用(0,40,80,160 mg/kg 4个水平)对Cd中度(0.72mg/kg)和重度(5.26mg/kg)污染土壤中Cd生物有效性及水稻Cd累积的差异。结果表明:施Zn对各检测指标存在影响,但土壤Cd总量仍是土壤Cd活性和水稻Cd累积差异变动的主控因素。在Cd中度污染土壤中,施Zn降低了土壤交换态Cd含量1.9%~17.0%,但水稻根表铁膜、根和糙米中Cd含量随Zn施用浓度的增大而增大,糙米Cd含量从0.09mg/kg上升到0.17mg/kg,相关分析显示糙米Cd含量与土壤交换态Zn含量显著正线性相关。在Cd重度污染土壤中,施Zn增大了土壤交换态Cd含量2.1%~4.8%,但降低了水稻各部位中Cd含量,当施Zn浓度超过80mg/kg时,糙米Cd含量可从对照组的0.45mg/kg降低到0.12mg/kg,符合国家食品污染物限量标准(GB 2762-2017)的要求,相关分析显示糙米Cd含量与土壤交换态Zn含量显著负线性相关。对2种Cd污染程度的土壤,施Zn均可增大Cd在水稻地下部的累积率,从而降低水稻地上部Cd的累积率。在Cd重度污染土壤中,可通过施Zn降低糙米Cd含量,施Zn量80mg/kg是试验中最佳施用量;但在Cd中度污染土壤中,施Zn有增大糙米Cd含量的风险。     

生物炭对水稻-再生稻体系吸收土壤中Cd和Pb的影响

以矿区周边Cd—Pb复合污染的农田土壤为供试材料,设置0,2.5%和5%(w/w)3个生物炭添加处理,通过盆栽试验探讨生物炭对再生稻吸收土壤中Cd和Pb的影响。结果表明,生物炭施加提高土壤pH和有机质含量,使Cd和Pb从移动性较强的弱酸提取态转化为较稳定的可还原态,且土壤CaCl2提取的有效态Cd和Pb含量分别降低33.23%~53.23%和66.52%~91.45%。同时,生物炭抑制Cd在头季和再生季水稻叶到糙米中的迁移,降低Pb从茎到叶和糙米的迁移,从而减少Cd和Pb在糙米中的累积;在5%生物炭处理下,再生季糙米Cd含量为0.15mg/kg,低于食品安全国家标准限量值(0.2mg/kg);Pb含量比对照处理降低68.18%。此外,再生季糙米中Cd和Pb含量低于头季稻糙米中相应的含量。因此,生物炭可以抑制Cd和Pb在再生稻体内的累积,降低糙米的重金属污染风险。     

重金属超富集植物龙葵对镉响应的蛋白组学分析

龙葵是典型的重金属超富集植物,但是我们对其重金属耐受和超富集的分子机理仍不完全清楚。为了从蛋白组学层面探究重金属超富集植物龙葵如何响应金属镉,本研究采用双向电泳和MALDI-TOF MS分析方法,鉴定了重金属超富集植物龙葵叶片和根中Cd胁迫下差异表达的蛋白。双向电泳在根和叶片中分别至少得到927和1 025个蛋白点,其中Cd胁迫下差异表达的蛋白点在根中有45个,叶片中有57个。采用MALDITOF MS分析,在根和叶片中分别鉴定了9个和12个蛋白点,分别代表了9个和6个差异表达的蛋白。生物信息学分析表明,这些蛋白涉及到激素合成、防御响应、能量代谢和细胞结构等。这些结果为进一步揭示重金属超富集植物龙葵响应Cd胁迫的分子调节机制,以及为通过现代生物技术手段进行重金属污染的植物修复提供了理论依据。     

A Meta-Analysis on Phenotypic Variation in Cadmium Accumulation of Rice and Wheat: Implications for Food Cadmium Risk Control

In some densely-populated countries, farmland has been widely cadmium (Cd) contaminated, and the utilization of the contaminated farmland for crop production is currently unavoidable. This necessitates the use of low-Cd crops (i.e., pollution-safe cultivars, the crop varieties with the ability to accumulate a low level of Cd in their edible parts when grown on polluted soil) in these areas and highlights the importance of knowledge on phenotypic variation in crop Cd accumulation for food Cd risk control. Studies on phenotypic variation in heavy metal accumulation started decades ago for a wide range of crops, and synthesis of the scattered experimental results in the literature is in need. We built a Low-Cd Crops Database based on literature research, and relevant meta-analysis was performed to quantitatively explore the phenotypic variation in Cd uptake and translocation of rice and wheat. Considerable variability existed among rice (median grain Cd bioconcentration factor (BCF) of 0.10) and wheat (median grain Cd BCF of 0.21) phenotypes in grain Cd accumulation, and this variability was labile to soil pH and the level of Cd stress. Wheat statistically had a higher root-to-shoot Cd-translocating ability than rice, highlighting potential food Cd risks and the importance of growing low-Cd wheat in slightly Cd-contaminated regions. Meanwhile, no correlations were detected among soil-to-root, root-to-shoot, and shoot-to-grain translocation factors, implying that Cd uptake and internal translocation in crops were probably controlled by different underlying genetic mechanisms. Root-to-shoot Cd transport could be a favorable target trait for selecting and breeding low-Cd rice and wheat. In all, this review provides a comprehensive low-Cd crop list for remediation practice and a systematic meta-analysis inferring food Cd risks based on plant capacity for Cd accumulation and desired traits for low-Cd crop breeding.     

A review of cadmium sorption mechanisms on soil mineral surfaces revealed from synchrotron-based X-ray absorption fine structure spectroscopy: Implications for soil remediation

The sorption of cadmium(Cd) is one of the most important chemical processes in soil, affecting its fate and mobility in both soil and water and ultimately controlling its bioavailability. In order to fundamentally understand the sorption/desorption of Cd in soil systems, X-ray absorption fine structure spectroscopy(XAFS) has been applied in numerous studies to provide molecular-level information that can be used to characterize the surface adsorption and precipitation reactions that Cd can undergo. This information greatly improves our current knowledge of the possible chemical reactions of Cd in soil. This paper critically reviews the mechanisms of Cd sorption/desorption at the mineral-water interface based on XAFS studies performed over the past twenty years. An introduction to the basic concepts of sorption processes is provided, followed by a detailed interpretation of XAFS theory and experimental data collection and processing,ending finally with a discussion of the atomic/molecular-scale Cd sorption mechanisms that occur at the soil mineral-water interface. Particular emphasis is placed on literature that discusses Cd adsorption and speciation when associated with iron, manganese, and aluminum oxides and aluminosilicate minerals.Multiple sorption mechanisms by which Cd is sorbed by these minerals have been found, spanning from outer-sphere to inner-sphere to surface precipitation,depending on mineral type, surface loading, and pH. In addition, the application of complementary techniques(e.g.,113 Cd nuclear magnetic resonance(NMR) and molecular dynamics simulation) for probing Cd sorption mechanisms is discussed. This review can help to develop appropriate strategies for the environmental remediation of Cd-contaminated soils.     

Effect of Elemental Sulfur Supply on Cadmium Uptake into Rice Seedlings When Cultivated in Low and Excess Cadmium Soils

Effects of sulfur (S) (0, 30 mg S kg^?1 soil) supply on cadmium (Cd) uptake into rice when cultivated in low-Cd soil [38.8 μg kg^?1 for diethylenetriaminepentaacetic acid (DTPA)–extractable Cd] and in excessive-Cd soil (748.7 μg kg^?1 for DTPA-extractable Cd) were investigated in a combined soil–sand culture experiment. The significant difference in the Cd uptake into rice between –S and +S treatments were observed in relation to soil Cd levels. When rice was exposed to excessive Cd soil, application of S restrained the uptake of Cd into rice, the S supply tended to increase Cd uptake into rice when cultivated in low-Cd soil. The possible mechanisms explaining the interactions among soil Cd level, S supply, and Cd accumulation in rice are proposed. These results suggest that S fertilization may be important for the development approaches to reducing Cd accumulation in rice when cultivated Cd-contaminated soils.     

青葙修复镉污染土壤的田间试验研究

为探索氯化铵与柠檬酸和青葙(Celosia argentea L.)联合修复重金属Cd污染土壤的方法,通过田间试验,研究了氯化铵与柠檬酸对青葙生长和吸收富集Cd的影响、根际土与非根际土之间的差异,以及对土壤Cd含量和形态的影响。结果表明,种植青葙并施加氯化铵(C+AC)处理能显著促进青葙地上部干重的提高,比只种植青葙(C)处理增产53.03%;种植青葙并施加柠檬酸(C+CA)处理能提高青葙对Cd的吸收富集能力,地上部Cd含量比C处理提高16.64%;而C+AC处理对青葙地上部Cd积累量的促进效果最佳,比C处理提高69.49%;青葙的种植均显著降低根际土Cd的酸溶态含量,C、C+AC和C+CA处理的降低幅度分别为10.31%,15.00%和12.67%,显著大于非根际土;C+CA处理的土壤Cd含量降率最大,为5.33%,而不种植青葙,不施加药剂(CK)处理为1.43%,只有C+CA处理的26.83%。因此,青葙植物提取对Cd的降低仍起关键作用,且施加柠檬酸对表层土壤Cd的修复性能最好。     

硒与黄腐酸组配对水稻镉吸收的影响

以Cd污染水稻土为研究对象,采用盆栽试验研究不同用量Se(0.5,1.0 mg/kg)与黄腐酸(0.6,1.2 g/kg)组配对水稻吸收积累镉的影响,并探讨其作用机理,以期为Cd污染稻田的安全利用提供科学依据。结果表明:单施Se可使土壤pH提高0.08～0.23个单位,土壤CaCl_2提取态Cd含量降低8.6%～20.9%,水稻地上部各器官Cd含量显著降低29.4%～39.5%,单施Se能有效降低水稻吸收Cd,并阻控Cd向地上部以及籽实中的转运。单施黄腐酸能显著降低土壤pH,但对土壤CaCl_2—Cd含量、水稻各器官Cd和Se含量(除低量黄腐酸处理叶片和糙米Cd含量外)及水稻各器官Cd的分配无显著影响。Se与黄腐酸组配对土壤pH的影响取决于二者的用量,黄腐酸与高量Se组配处理显著降低CaCl_2提取态Cd 16.5%～21.9%。Se与黄腐酸组配处理能显著减少水稻Cd的吸收及向地上部和籽粒的转运,更为有效地降低稻米Cd含量,高量Se与黄腐酸组配的2个处理与对照相比,稻米Cd含量分别降低38.1%和50.2%。总体来看,施Se能有效降低稻米Cd含量,而Se与黄腐酸配合施用降Cd效果更佳。     

接种耐铬细菌菌株对二月兰中铬积累及其生长状况的影响

Beneficial interactions between microorganisms and plants, particularly in the rhizosphere, are a research area of global interest. Four cadmium （Cd）-tolerant bacterial strains were isolated from heavy metal-contaminated sludge and their effects on Cd mobility in soil and the root elongation and Cd accumulation of Orychophragmus violaceus were explored to identify the capability of metal- resistant rhizobacteria for promoting the growth of O. violaceus roots on Cd-contaminated soils. The isolated strains, namely, Bacillus subtilis, B. cereus, B. megaterium, and Pseudomonas aeruginosa, significantly enhanced the plant Cd accumulation. The Cd concentrations in the roots and shoots were increased by up to 2.29- and 2.86-fold, respectively, by inoculation of B. megaterium, as compared with the uninoculated control. The bacterial strains displayed different effects on the shoot biomass. Compared with the uninoculated plants, the shoot biomass of the inoculated plants was slightly increased by B. megaterium and significantly decreased by the other strains. B. megaterium was identified as the best candidate for enhancing Cd accumulation in O. violaceus. Thus, this study provides novel insight into the development of plant-microbe systems for phytoremediation.     

Breeding of a practical rice line ‘TJTT8’ for phytoextraction of cadmium contamination in paddy fields

ABSTRACT

Previously, we showed that qCdp7, an allele identified in the high-Cd-accumulating indica rice variety ‘Jarjan,’ is associated with effective phytoextraction of Cd from paddy soils. However, ‘Jarjan’ may not be practical for phytoextraction because it is susceptible to seed shattering and culm lodging, which are unfavorable traits for mechanical rice harvesting. In this study, to develop a practical rice line for phytoextraction, we introduced the qCdp7 allele into ‘Tachisugata,’ a rice variety with a nonshattering habit and lodging resistance, to produce a new high-Cd-accumulating rice line designated ‘TJTT8.’ This line inherited high-Cd accumulation and brown pericarps from ‘Jarjan’ and a nonshattering habit and lodging resistance from ‘Tachisugata;’ all of these traits are necessary for rice intended for Cd phytoextraction in Japan. Backcross inbred lines (BILs) were produced by two backcrosses to ‘Tachisugata’ after a cross between ‘Jarjan’ and ‘Tachisugata.’ ‘TJTT8’ was selected from the BILs by means of marker-assisted selection and phenotypic evaluation. When ‘TJTT8,’ the parents, and ‘Cho-ko-koku’ which is a high-Cd-accumulating indica variety were cultivated in Cd-contaminated paddy fields in four locations in Japan, ‘TJTT8’ exhibited lodging resistance and shattering resistance that were higher than those of ‘Jarjan’ and ‘Cho-ko-koku’ and equivalent to those of ‘Tachisugata.’ ‘TJTT8’ accumulated Cd in the aerial parts of the plants at concentrations ranging from 6.5 to 22.7 mg m^?2: it showed significantly higher Cd accumulation than ‘Tachisugata’ and was equivalent to ‘Jarjan’ and slightly superior to ‘Cho-ko-koku.’ Soil Cd concentration was estimated to have been reduced by 8.7–33.6% based on the amount of Cd accumulation in the aerial parts of the plants. Thus, we succeeded in using the qCdp7 allele to produce a practical rice line for Cd phytoextraction by improving several agronomic traits for compatibility with Japanese cultivation systems.     

Magnesium slag for remediation of cadmium- and arsenic-contaminated paddy soil: A field study

The accumulation of heavy metals like cadmium (Cd) and metalloids like arsenic (As) in plants can do harm to human health through the food chain, especially through the rice (Oryza sativa L.). To solve this problem, this study researched the application of magnesium slag (MS) and polyaspartic acid (PASP), which could accelerate rice growth and improve yield, increase soil pH and activate rice enzyme activity as well as reduce the bioavailability of Cd and As in the soil. After these two different treatments, rice yield increased by 17.0% and 18.9%, respectively. Meanwhile, the bioavailable As decreased by 49.1% and 42.5%, while the bioavailable Cd reduced by 72.6% and 44.3%. Besides, the Cd content in rice grains reduced by 77.7% and 17.3%, respectively, after two different treatments. In the MS treatment, the As content in rice grains was reduced by 21.8%, but showed no significant response to the other treatment. The contents of bioavailable Cd and As (determined by one-step extraction) in soil were decreased by MS and PASP, which was favourable for the reduction of Cd and As accumulation in rice. The health risk assessment showed that the application of passivators can effectively reduce the risk of carcinogenesis, but it was still unacceptable. The application dose of MS and PASP still needs further exploration.     

Use of Drinking Water Treatment Residuals in Reducing Bioavailability of Metals in Biosolid-Amended Alkaline Soils

This greenhouse study evaluated the use of drinking-water-treatment residuals (WTRs) to reduce the bioavailability of metals in the biosolid-amended agricultural alkaline soils. Results showed that increasing the application rate of biosolids increased the accumulation of lead (Pb), nickel (Ni), copper (Cu), and cadmium (Cd) in corn (Zea mays cv. single hybride 10), with greater metal concentrations in roots than in shoots. However, the addition of WTRs (1–4%, w/w) to the soil amended with 3% biosolids significantly (P < 0.05) decreased the concentrations of soil diethylenetriaminepentaacetic acid (DTPA)–extractable metals. The accumulation of Pb, Ni, Cu, and Cd in corn significantly correlated with the DTPA-extractable metal concentrations in the soils. Plant metal concentrations were significantly affected by the soil type, application rates of biosolids and WTRs, and the ratio of WTRs to biosolids in the soils. The 1:1 application ratio of WTRs to biosolids at the 3% application rate effectively reduced the accumulation of metals in corn tissues.     

菌渣生物炭对镉污染土壤性质及小白菜吸收镉的影响

为探讨以菌渣为原料制备的生物炭修复重金属镉污染土壤的可行性。采用盆栽试验,以香菇菌渣生物炭(SC)和平菇菌渣生物炭(PC)为研究对象,设置0.5%,1%,2%的生物炭施用量(w/w,%),研究其对镉污染土壤理化性质、土壤各形态镉分布、小白菜生长及镉吸收的影响。结果表明:施用SC和PC均能显著提高土壤pH和有机质(SOM)含量。与对照相比,2%的生物炭处理,土壤pH分别提高1.05和1.10个单位,SOM含量分别提高80.6%和61.2%。施用SC和PC使土壤可交换态镉降低,而提高残渣态镉含量。相关分析表明,土壤可交换态镉与pH、SOM和蔗糖酶呈显著负相关。与对照相比,2%处理下SC和PC显著降低小白菜镉含量,分别降低57.5%和54.1%;1%用量下小白菜产量分别提高53.4%和41.6%,表明高投加量菌渣生物炭对小白菜生长有不利影响。总体看来,SC和PC均有利于改善土壤性质,减轻镉对植物的毒害,促进小白菜生长。     

Effect of soil zinc,pH, and cultivar on cadmium uptake in leaf lettuce (Lactuca sativa L. var. crispa)

Abstract

Six noncrisphead lettuce cultivars (Lactuca sativa L.) were grown in pots, using soil from field plots that had been amended annually with 90 MT/ha of an industrial sludge as part of a continuous study initiated in 1981. Two greenhouse experiments (each replicated 6 times) were completed—one in the spring and one in the fall. Variables included 6 cultivars, 2 soil pH levels and 2 soil Zn levels. All variables appeared to influence Cd accumulation in the leaf tissue. Uptake of Cd and Zn increased with decreasing soil pH for all cultivars. ‘Grand Rapids’ accumulated the least leaf Cd and ‘Summer Bibb’ the most. A positive correlation between leaf Zn and leaf Cd was observed, but the correlation between soil Zn and leaf Cd was variable.     

Cadmium Uptake and Distribution by Different Maize Genotypes in Maturing Stage

Abstract

A pot experiment was conducted to investigate the effects of different cadmium (Cd) concentrations of phaeozem on growth and uptake of Cd and mineral nutrient copper (Cu) and zinc (Zn) by three maize genotypes in the mature stage. The results showed that the dry‐matter accumulation of shoots was inhibited by added Cd for Jidan209 and Jitian6, but this did not influence Chunyou30. The root biomasses decreased significantly for Jitian6 and stimulated Jidan209 and Chunyou30. Yields of three genotypes of maize were decreased by increasing soil Cd concentrations. Among them, Chunyou30 had a high tolerance and Jitian6 was most sensitive to Cd. The accumulation order of Cd in different parts of plants was root > leaf > stem > grain. The percentage of absorbed Cd by roots was 70–85% of total absorbed amount. Cadmium uptake by maize in the mature stage had a significant genetic variation: Jitian6 > Jidan209 > Chunyou30 for root, stem and leaf, and Jidan209 > Jitian6 > Chunyou30 for grain, respectively. Increase of soil Cd had no significant effect on Zn concentration of leaves, but there was a significant genetic variation: Chunyou30 > Jidan209 > Jitian6 (P=0.023). Cu concentration of leaves was increased significantly with increase of soil Cd (P<0.01), but no genetic variation was observed.     

Heavy-Metal Bioavailability and Chelate Mobilization Efficiency in an Assisted Phytoextraction Process by Sesbania sesban (L.) Merr

Chelate-induced phytoextraction is an innovative technique for cleaning metal- contaminated soil. The present study evaluates the degree of metal mobilization in soil and enhancement of phytoextraction of cadmium (Cd), lead (Pb), and zinc (Zn) by Sesbania sesban (L.) Merr. from artificially contaminated soil by application of ethylenediaminetetraacetic acid (EDTA). After 30 days of plant growth, the pots were divided into three sets (0.0, 2.5, and 5.0 mmol EDTA per kg soil). Experimental results indicated that levels of diethylenetriaminepentaacetic acid (DTPA)–extractable metals and metals in the leachate decreased as the EDTA dose increased. Plant growth parameters and total chlorophyll contents in the plants with EDTA applied were less than those of control. However, EDTA application significantly reduced metal accumulation in root and increased metal accumulation in the shoot of plants; similar results were obtained for the bioconcentration factor and translocation factor. The application of 5 mmol EDTA kg^?1 to metal-spiked soil may be an efficient alternative for the chemically enhanced phytoextraction by S. sesban.