Cd Concentrations In Plants Research Articles

Heavy Metals Accumulation in the Edible Parts of some Sewage Wastewater Irrigated Vegetable Crops

Nowadays, using sewage wastewater in the irrigated agriculture causes hazardous environment impacts. Assessment of these negative effects is vital issue to prevent heavy metals to be introduced in the food chain. Field and laboratory studies were conducted at Ellwan, Mangabad and El-Madabegh villages, Assiut Governorate, in order to evaluate heavy metals concentrations in the edible parts of carrot, turnip and onion plantswhich were irrigated with sewage water (SW). The obtained results indicated that, the soils of the studied villages were contaminated by heavy metals. The concentrations of Zn, Cu, Pb, Cd and Ni concentrations in the edible portion of thesevegetables plants ranged between 45-70, 13-19, 3.8-6.2, 2.85-3.85 and 2-6 mgkg–1, respectively. The obtained results showed that the concentrations of Pb, Cd and Ni in the edible plants were higher than the permissible limit levels but those of Zn and Cu were within the safe limit levels. It is worthy to mention that the irrigated edible vegetable crops especially onion, turnip and carrot with SW should be avoided. This study highlights the potential hazard for human health due to uptake of high concentrations of heavy metals especially Ni, Cd and Pb by the studied vegetable crops.

Identifying the functional groups and the influence of synthetic chelators on Cd availability and microbial biomass carbon in Cd-contaminated soil

ABSTRACTSynthetic chelators play an important role in boosting the microbial biomass carbon (MBC), dissolved organic carbon (DOC), and heavy metal solubility in a contaminated soil toward a sustainability of environment for agricultural crops. Castor plant was grown under different levels of Cd contaminated soil (−Cd and +Cd) following adding three chelating agents, ethylenediaminetetraacetic acid (H4EDTA), nitriloacetic acid (H3 NTA), and NH4 citrate (ammonium citrate) to the soil at rates of 10, 15, and 25 mmol in 5 kg of soil per pot. The highest bioavailable Cd concentrations in soil and castor plant were obtained from NH4 citrate and H4EDTA treatments in the contaminated soil. Fourier transform infrared (FTIR) analysis showed that NH4 citrate was the most effective chelator in Cd-contaminated soil. MBC and DOC contents were significantly increased and reached at 81.98–80.37 and 1.96–1.90 mg kg−1 respectively, in the (H3 NTA) and NH4 citrate treatments in Cd-contaminated soil. Further research is needed to investigate the use of chelators in the phytoextraction of Cd-contaminated soils under field conditions and whether it may be beneficial in accelerating the phytoextraction of Cd through hyperaccumulating plants.

Estimation of Cadmium uptake by tobacco plants from laboratory leaching tests

ABSTRACTThe objective of the present study was to determine the impact of cadmium (Cd) concentration in the soil on its uptake by tobacco plants, and to compare the ability of diverse extraction procedures for determining Cd bioavailability and predicting soil-to-plant transfer and Cd plant concentrations. The pseudo-total digestion procedure, modified Tessier sequential extraction and six standard single-extraction tests for estimation of metal mobility and bioavailability were used for the leaching of Cd from a native soil, as well as samples artificially contaminated over a wide range of Cd concentrations. The results of various leaching tests were compared between each other, as well as with the amounts of Cd taken up by tobacco plants in pot experiments. In the native soil sample, most of the Cd was found in fractions not readily available under natural conditions, but with increasing pollution level, Cd amounts in readily available forms increased. With increasing concentrations of Cd in the soil, the quantity of pollutant taken up in tobacco also increased, while the transfer factor (TF) decreased. Linear and non-linear empirical models were developed for predicting the uptake of Cd by tobacco plants based on the results of selected leaching tests. The non-linear equations for ISO 14870 (diethylenetriaminepentaacetic acid extraction – DTPA), ISO/TS 21268-2 (CaCl2 leaching procedure), US EPA 1311 (toxicity characteristic leaching procedure – TCLP) single step extractions, and the sum of the first two fractions of the sequential extraction, exhibited the best correlation with the experimentally determined concentrations of Cd in plants over the entire range of pollutant concentrations. This approach can improve and facilitate the assessment of human exposure to Cd by tobacco smoking, but may also have wider applicability in predicting soil-to-plant transfer.

Influence of cadmium stress on root exudates of high cadmium accumulating rice line (Oryza sativa L.)

A hydroponic experiment with two different cadmium (Cd) accumulating rice lines of Lu527-8 (the high Cd accumulating rice line) and Lu527-4 (the normal rice line) was carried out to explore the links among Cd stress, root exudates and Cd accumulation. The results showed that (1) Cd stress increased quantities of organic acids, but had no effect on composition in root exudates of the two rice lines. In Cd treatments, the contents of every detected organic acid in root exudates of Lu527-8 were 1.76–2.43 times higher than those of Lu527-4. Significant positive correlations between organic acids contents and Cd contents in plants were observed in both rice lines, except that malic acid was only highly relevant to Lu527-8, but not to Lu527-4. (2) Both composition and quantities of amino acids in root exudates changed a lot under Cd stress and this change differed in two rice lines. In control, four amino acids (glutamic acid, glycine, tyrosine and histidine) were detected in two rice lines. Under Cd stress, eight amino acids in Lu527-8 and seven amino acids in Lu527-4 could be detected, among which phenylalanine was only secreted by Lu527-8 and alanine, methionine and lysine were secreted by both rice lines. The contents of those four newly secreted amino acids from Lu527-8 increased significantly with the increase of Cd dose and each had a high-positive correlation with Cd contents, but the same change did not appear in Lu527-4. The difference between two rice lines in secretion of organic acids and amino acids may be related to their different Cd uptake properties.

Biochar application increased the growth and yield and reduced cadmium in drought stressed wheat grown in an aged contaminated soil

Cadmium (Cd) and drought stress in plants is a worldwide problem, whereas little is known about the effect of biochar (BC) under combined Cd and drought stress. The current study was conducted to determine the impact of BC on Cd uptake in wheat sown in Cd-contaminated soil under drought stress. Wheat was grown in a soil after incubating the soil for 15 days with three levels of BC (0%, 3.0% and 5.0% w/w). Three levels of drought stress (well-watered, mild drought and severe drought containing 70%, 50%, and 35% of soil water holding capacity respectively) were applied to 45-d-old wheat plants. Drought stress decreased plant height, spike length, chlorophyll contents, gas exchange parameters, root and shoot dry biomasses and grain yields. Drought stress also caused oxidative stress and decreased the antioxidant enzymes activities whereas increased the Cd concentration in plants. Biochar increased morphological and physiological parameters of wheat under combined drought and Cd stress and reduced the oxidative stress and Cd contents and increased antioxidant enzymes activities. The decrease in Cd concentration with BC application in drought-stressed plant might be attributed to BC-induced increase in crop biomass production and reduction in oxidative stress. These results indicate that BC could be used as an amendment in metal contaminated soil for improving wheat growth and reducing Cd concentrations under semiarid conditions.

Determination and validation of soil thresholds for cadmium based on food quality standard and health risk assessment

Cadmium (Cd) is an environmental toxicant with high rates of soil-plant transfer. It is essential to establish an accurate soil threshold for the implementation of soil management practices. This study takes root vegetable as an example to derive soil thresholds for Cd based on the food quality standard as well as health risk assessment using species sensitivity distribution (SSD). A soil type-specific bioconcentration factor (BCF, ratio of Cd concentration in plant to that in soil) generated from soil with a proper Cd concentration gradient was calculated and applied in the derivation of soil thresholds instead of a generic BCF value to minimize the uncertainty. The sensitivity variations of twelve root vegetable cultivars for accumulating soil Cd and the empirical soil-plant transfer model were investigated and developed in greenhouse experiments. After normalization, the hazardous concentrations from the fifth percentile of the distribution based on added Cd (HC5add) were calculated from the SSD curves fitted by Burr Type III distribution. The derived soil thresholds were presented as continuous or scenario criteria depending on the combination of soil pH and organic carbon content. The soil thresholds based on food quality standard were on average 0.7-fold of those based on health risk assessment, and were further validated to be reliable using independent data from field survey and published articles. The results suggested that deriving soil thresholds for Cd using SSD method is robust and also applicable to other crops as well as other trace elements that have the potential to cause health risk issues.

Can liming reduce cadmium (Cd) accumulation in rice (Oryza sativa) in slightly acidic soils? A contradictory dynamic equilibrium between Cd uptake capacity of roots and Cd immobilisation in soils

Cadmium (Cd) accumulation in rice is strongly controlled by liming, but information on the use of liming to control Cd accumulation in rice grown in slightly acidic soils is inconsistent. Here, pot experiments were carried out to investigate the mechanisms of liming on Cd accumulation in two rice varieties focusing on two aspects: available/exchangeable Cd content in soils that were highly responsive to liming, and Cd uptake and transport capacity in the roots of rice in terms of Cd accumulation-relative gene expression. The results showed that soil availability and exchangeable iron, manganese, zinc and Cd contents decreased with increased liming, and that genes related to Cd uptake (OsNramp5 and OsIRT1) were sharply up-regulated in the roots of the two rice varieties. Thus, iron, manganese, zinc and Cd contents in rice plants increased under low liming applications but decreased in response to high liming applications. However, yield and rice quantities were only slightly affected. These results indicated that Cd accumulation in rice grown in slightly acidic soils presents a contradictory dynamic equilibrium between Cd uptake capacity by roots and soil Cd immobilisation in response to liming. The enhanced Cd uptake capacity under low liming dosages increases risks to human health.

A DOC coagulant, gypsum treatment can simultaneously reduce As, Cd and Pb uptake by medicinal plants grown in contaminated soil

The efficiency of gypsum, as a dissolved organic carbon (DOC) coagulator, for the simultaneous immobilization of two heavy metals (Cd and Pb) and one metalloid (As) in agricultural soils near an abandoned mining site was examined. The agricultural soil was defined as long-term contaminated as As (1540mgkg−1), Cd (55mgkg−1) and Pb (1283mgkg−1) concentrations exceeded the Korean guideline values for As (25mgkg−1), Cd (4mgkg−1), and Pb (200mgkg−1). Gypsum was incorporated into the contaminated soil at 3% (w/w). In comparison two commonly using immobilizing agents (lime and compost), together with a mixture (lime+gypsum) were also included in the pot trial for the cultivation of two medical plants (A. gigas and A. macrocephala) and to evaluate the effectiveness of gypsum on As, Cd and Pb immobilization. The results showed that even though pH change-induced immobilizing agents such as lime were more effective than gypsum at immobilizing Cd and Pb, addition of gypsum also effectively reduced heavy metal phytoavailability as indicated by decreases in the concentration of Cd and Pb in medicinal plants. Furthermore, gypsum and gypsum+ lime were also most effective in reducing As concentrations in both plants studied. This was mainly attributed to significant decreases in soil DOC (48–64%) when gypsum and gypsum+lime were applied to the soil. Consequently, it was concluded that enhanced DOC coagulation with gypsum, could be considered as a promising technique for the immobilization of both metals (Cd and Pb) and metalloids (As) in agricultural soils.

Exogenous ethylene enhanced the cadmium resistance and changed the alkaloid biosynthesis in Catharanthus roseus seedlings

Cadmium (Cd) is not an essential nutrition element to plants and high concentration of Cd in the environment causes severe damage to plants. It is reported that the gas phytohormone ethylene plays important roles in plant responses to Cd stress. However, whether plant secondary metabolism is involved in this process remains to be investigated. Here, the regulations of exogenous ethylene on internal Cd accumulation and terpenoid indole alkaloids (TIAs) biosynthesis in the medicinal plant Catharanthus roseus (L.) G. Don (C. roseus) under Cd stress condition were explored. Our results showed that Cd treatment inhibited biomass accumulation, increased Cd accumulation and H2O2 and malondialdehyde (MDA) productions. Simultaneously, Cd treatment enhanced yields of vindoline, catharanthine and vinblastine, as well as the gene expressions of TIAs pathway enzymes at transcriptional level. Exogenous ethylene application significantly reduced the Cd content in whole plants and the H2O2 and MDA productions in roots and leaves, indicating that Cd stress in C. roseus was effectively alleviated by the ethylene application. It was interesting to find that exogenous ethylene promoted the Cd transport from roots to leaves and the value of Cd TF (transfer factor) was increased from 0.41 to 0.53. In leaves, the transcriptional expression of metallothionein (MT) was up-regulated by exogenous ethylene application, together with the increase of Cd accumulation. Additionally, exogenous ethylene reduced the TIAs productions, with an exception of catharanthine in leaves. The transcriptional expressions of alkaloid transporters, triose phosphate translocator (MDR) and multidrug resistance (TPT) were also up-regulated in leaves by exogenous ethylene, in accordance with the change of catharanthine biosynthesis. All of our results showed that exogenous ethylene could elevate the Cd resistance of C. roseus and effectively influence TIAs biosynthesis in C. roseus. Regulations of ethylene on the transcriptional expressions of MT, pathway enzymes and alkaloid transporters might be involved in this process.

Comparative study on the effects of putrescine and spermidine pre-treatment on cadmium stress in wheat

In several cases a correlation was found between polyamines and abiotic stress tolerance. However, the individual polyamines may have different effects, which also vary depending on the type of treatment. When applied as seed soaking or added hydroponically 0.5mM putrescine and spermidine, different changes were induced during 50µM cadmium stress in wheat plants. Seed-soaked plants were exposed to cadmium immediately after germination for 5 days, while plants pre-treated with polyamines hydroponically were stressed at age of 14 days for 7 days.Putrescine pre-treatment was beneficial both as seed soaking and applied hydroponically, while spermidine only had a protective effect in the case of seed soaking, enhancing the Cd-induced oxidative stress when were pre-treated hydroponically. The differences observed were related to the polyamine metabolism. The accumulation of endogenous putrescine beyond a certain amount may be in relation with the negative effect of hydroponic spermidine pre-treatment during Cd stress. The increased putrescine content was also correlated with the highest accumulation of Cd, salicylic acid and proline contents in plants treated with a combination of spermidine and Cd. However, the expression level of the gene encoding phytochelatin synthase was only influenced by hydroponically applied spermidine, which decreased it under cadmium stress. Changes in the activities of antioxidant enzymes, diamine and polyamine oxidases were also discussed.

Modulation of the efficiency of trace metal phytoremediation by Sedum plumbizincicola by microbial community structure and function

Recent research on the rhizosphere microbiome indicates that plants may benefit more from microbial communities than from individual members in a community. The link between soil microbiome and plant performance remains poorly understood during trace metal phytoremediation by hyperaccumulator plants. The effect of different microbiomes on the cadmium (Cd)/zinc (Zn) phytoextraction efficiency of Sedum plumbizincicola was therefore explored. Different microbiomes were set up using γ-irradiation and vancomycin addition and a pot experiment was conducted. The microbial communities were characterized using high-throughput sequencing and their functions were predicted. Plant Cd and Zn contents in the vancomycin-amended treatment were about 38–46% and 35%–53% respectively lower than those in the other treatments. Bacterial composition and diversity were substantially changed by γ-irradiation and vancomycin addition but plant trace metal accumulation did not change subsequently. The bacterial functional profiles were very different following treatment with vancomycin compared with the other treatments at KEGG orthology hierarchy level 3. Genes related to up-regulated biofilm formation and down-regulated siderophore synthesis may partly contribute together to the low plant trace metal accumulation following vancomycin treatment. Specific bacterial community function rather than bacterial community diversity and composition may affect trace metal uptake by hyperaccumulator plants.

Effect of zinc-lysine on growth, yield and cadmium uptake in wheat (Triticum aestivum L.) and health risk assessment

Cadmium (Cd) is among the most widespread toxic trace elements found in agricultural soils due to various anthropogenic activities. The role of micronutrient-amino chelates on reducing Cd toxicity in crop plants is recently introduced. The current study was conducted to highlight the role of foliar application of zinc-lysine (Zn-lys) complex on biochemical and growth parameters and Cd uptake in wheat (Triticum aestivum) grown in aged Cd-contaminated soil. Foliar concentration of Zn-lys (0, 10, 20, and 30 mg L−1) was applied at different time intervals (2nd, 3rd, 5th and 7th week of sowing) and plants were harvested at maturity. Folliar application of Zinc-lys significantly increased the photosynthesis, grain yield, enzyme activities and Zn contents in different plant tissues. Zinc-lys reduced Cd contents in grains, shoot and root as well as reduced the oxidative stress in wheat linearly in a dose-additive manner. Taken together, Zn-lys chelate efficiently improved wheat growth and fortified Zn contents while reduced Cd concentration in plant in a Zn-deficient Cd-contaminated soil. Although, health risk index (HRI) from the soil sampling area seems to be lower than <1 for Cd but may exceed due to long-term consumption of grains produced from such contaminated soil. Foliar applied Zn-lys reduced HRI which may help to reduce health risks associated with Cd.

Foliar application of aspartic acid lowers cadmium uptake and Cd-induced oxidative stress in rice under Cd stress.

Cadmium (Cd) contamination of farmland soils is a widespread problem around the globe, and rice (Oryza sativa L.) tends to accumulate more Cd and is considered as one of the major sources of Cd intake in humans, especially consuming rice-derived products. The current study investigated the effects of foliar applied aspartic acid (Asp) on growth parameters, biomass, chlorophyll concentration, gas exchange characteristics, Cd uptake, and antioxidative capacity in the shoots and roots of rice seedlings exposed to Cd stress. For this, 30-day-old rice nursery was transferred in the soil with aged Cd contamination (2.86mgkg-1). After 2weeks of growth, different concentrations (0, 10, 15, and 20mgL-1) of Asp were foliar applied four times with a 7-day interval, and the crop was harvested after 10weeks of transplanting. Foliar applied Asp increased the plant height, shoot and root dry weight, chlorophyll concentration, and gas exchange parameters, while it reduced the Cd concentrations in both shoots and roots as well as shoot to root Cd translocation factor compared to the control. Foliar application of Asp reduced the malondialdehyde content and electrolyte leakage in rice parts compared to the control in a dose-additive manner. The activities of key antioxidant enzymes increased while peroxidase activity decreased by exogenous Asp. The increase in plant weight and photosynthesis might be due to lower Cd concentrations in plants which may reduce the oxidative stress and also help the plants to minimize direct damage caused by Cd to the photosynthetic organs.

Effects of Exogenous Nitric Oxide and 24-Epibrassinolide on the Physiological Characteristics of Peanut Seedlings Under Cadmium Stress

Cadmium (Cd) is highly toxic to plants, animals, and humans. Limited information is available on the role of nitric oxide (NO) and/or 24-epibrassinolide (EBR) in response of plants to Cd stress. In this study, a hydroponic experiment was performed to investigate the effects of NO and/or EBR on peanut plants subjected to Cd stress (200 µmol L−1) with sodium nitroprusside (SNP, an exogenous NO donor) (250 µmol L−1) and/or EBR (0.1 µmol L−1) addition. The results showed that Cd exposure inhibited plant growth, and this stress was alleviated by exogenous NO or EBR, and especially the combination of the two. Treatment with Cd inhibited the growth of peanut seedlings, decreased chlorophyll content, and significantly increased the Cd concentration in plants. Furthermore, the concentration of reactive oxygen species (ROS) markedly increased in peanut seedlings under Cd stress, resulting in the accumulation of malondialdehyde (MDA) and proline in leaves and roots. Under Cd stress, applications of SNP, EBR, and especially the two in combination significantly reduced the translocation of Cd from roots to leaves, increased the chlorophyll content, decreased the concentrations of ROS, MDA, and proline, and significantly enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in peanut seedlings. Exogenous NO and/or EBR also stimulated the activities of nitrate reductase (NR) and nitric oxide synthase (NOS) and increased the contents of antioxidants, such as ascorbic acid (AsA) and reduced glutathione (GSH). Furthermore, exogenous NO and/or EBR enhanced Cd accumulation in the cell wall and thus decreased Cd distribution in the organelles in the roots. The concentrations of calcium (Ca), iron (Fe), magnesium (Mg), and zinc (Zn) were also regulated by exogenous NO or EBR, and especially by the two in combination. These results indicated that SNP and EBR, alone and particularly in combination, can mitigate the negative effects of Cd stress in peanut plants.

Effect of limestone, lignite and biochar applied alone and combined on cadmium uptake in wheat and rice under rotation in an effluent irrigated field

Cadmium (Cd) uptake and accumulation in crop plants, especially in wheat (Triticum aestivum) and rice (Oryza sativa) is one of the main concerns for food security worldwide. A field experiment was done to investigate the effects of limestone, lignite, and biochar on growth, physiology and Cd uptake in wheat and rice under rotation irrigated with raw effluents. Initially, each treatment was applied alone at 0.1% and combined at 0.05% each and wheat was grown in the field and then, after wheat harvesting, rice was grown in the same field without additional application of amendments. Results showed that the amendments applied increased the grain and straw yields as well as gas exchange attributes compared to the control. In both crops, highest Cd concentrations in straw and grains and total uptake were observed in control treatments while lowest Cd concentrations was observed in limestone + biochar treatment. No Cd concentrations were detected in wheat grains with the application of amendments except limestone (0.1%). The lowest Cd harvest index was observed in limestone + biochar and lignite + biochar treatments for wheat and rice respectively. Application of amendments decreased the AB-DTPA extractable Cd in the soil while increasing the Cd immobilization index after each crop harvest. The benefit-cost ratio and Cd contents in plants revealed that limestone + biochar treatment might be an effective amendment for increasing plant growth with lower Cd concentrations.

Dry cultivation enhances cadmium solubility in contaminated soils but minimizes cadmium accumulation in a leafy vegetable

Water management has a strong influence on Cd solubility in agricultural soils, affecting Cd uptake in crops. In the process, sulfur interaction with other metals such as zinc may play an important role. A pot experiment was carried out to investigate the effects of water management coupled with zinc and sulfate amendment on Cd uptake by the leafy vegetable amaranth with a strong Cd accumulation tendency in its edible parts. The soils were amended with Cd, Cd+SO4 and Cd+SO4+Zn with no amendment as control. Then, the soils were flooded for 1 month, after which amaranth was grown with soil kept saturated (wet cultivation). In the succeeding planting, soils were tilled to aeration condition under which amaranth was grown again (dry cultivation). Soil and crop samples were collected and analysed for various parameters. The readily exchangeable quantities of Cd and Zn in the soil decreased under wet cultivation, increasing again under dry cultivation but to levels lower than those in the initial soil. Wet cultivation enhanced plant Cd concentration but reduced Zn accumulation compared to dry cultivation. Zn bioavailability was strongly affected by soil water status but failed to reduce Cd uptake by amaranth. Irreversible or slowly reversible changes occurred in Cd and Zn solubility and phytoavailability as soil water-saturated status was altered by periodic flooding events. Dry cultivation with lower soil water content ensured high production with low Cd in the edible part of this leaf vegetable and so remains the recommended irrigation regime.

Effect of Nano Zeolites on pH, CEC in Soil and Cd Fractions in Plant and Soil at Different Cadmium Levels

Soil incubation experiment and pot experiment were carried out to investigate the influence of nano zeolite (NZ) and ordinary zeolite (OZ) on the soil pH, cation exchange capacity, concentration of soil Cd, soil Cd fraction and Cd uptake by Chinese cabbage when exposed to different Cd pollution levels(1, 5, 10 and 15 mg·kg-1). The results of soil incubation experiment showed that the nano zeolite and ordinary zeolite dose(5, 10 and 20 g·kg-1) increased the soil pH and cation exchange capacity, and decreased the concentration of soil exchangeable Cd, while increased the concentration of Cd in carbonate, Fe-Mn oxide, organic matter and residual fraction. The lowest EX-Cd was observed in the high nano zeolite (20 g·kg-1) treatment. The soil pH and cation exchange capacity was extremely negatively correlated with the concentration of soil exchangeable Cd(P<0.01),and extremely positively correlated with the concentration of soil Fe-Mn oxide Cd(P<0.01). The results of pot experiment showed that the FDC of exchangeable Cd in soil decreased by 6.4%-63.2%, and the FDC of water-extractable and ethnol-extractable Cd in Chinese cabbage decreased by 2.1%-56% and 11.8%-100% with zeolite application, respectively. Moreover, the reduction effect of nano zeolite on Cd concentration in soil and plant was better than that of ordinary zeolite. The FDC of Cd fraction in shoot of Chinese cabbage showed correlation with the FDC of carbonate Cd and organic matter Cd in soil(P<0.05) when exposed to 1 mg·kg-1 Cd pollution. Moreover, correlation was also found in the FDC of organic matter Cd and residual Cd in soil(P<0.05) under 5 mg·kg-1 Cd pollution.

Phytosiderophore-induced mobilization and uptake of Cd, Cu, Fe, Ni, Pb and Zn by wheat plants grown on metal-enriched soils

We investigated to which extent phytosiderophores (PS), released by grasses for the acquisition of iron, solubilize other metals in contaminated soils, and how this affects metal mobilization and uptake in wheat plants. A plant-based bioassay (‘RHIZOtest’) and batch extraction scheme were carried out for assessing metal mobilisation in soil, PS exudation and metal accumulation in wheat. Increased PS exudation was observed in Fe-deficient wheat, leading to enhanced Zn, Cu, Mn and Ni concentrations in wheat shoots on some soils. In contrast, plant Cd and Pb concentrations were not affected. Likewise, in the batch experiment, strongly increased extractable Cu, Ni and Zn concentrations were observed, in particular when 100 or 1000μM PS were added. Our results suggest that Fe deficiency can enhance the accumulation of some metals in shoots of grass species. Although our results indicate that the risk of enhanced accumulation of Cd and Pb in Fe deficient wheat shoots is rather small, further experiments conducted on soil for the complete vegetation period would be needed to confirm this observation.

Effects of calcium at toxic concentrations of cadmium in plants.

This review provides new insight that calcium plays important roles in plant growth, heavy metal accumulation and translocation, photosynthesis, oxidative damage and signal transduction under cadmium stress. Increasing heavy metal pollution problems have raised word-wide concerns. Cadmium (Cd), being a highly toxic metal, poses potential risks both to ecosystems and human health. Compared with conventional technologies, phytoremediation, being cost-efficient, highly stable and environment-friendly, is believed to be a promising green technology for Cd decontamination. However, Cd can be easily taken up by plants and may cause severe phytotoxicity to plants, thus limiting the efficiency of phytoremediation. Various researches are being done to investigate the effects of exogenous substances on the mitigation of Cd toxicity to plants. Calcium (Ca) is an essential plant macronutrient that involved in various plant physiological processes, such as plant growth and development, cell division, cytoplasmic streaming, photosynthesis and intracellular signaling transduction. Due to the chemical similarity between Ca and Cd, Ca may mediate Cd-induced physiological or metabolic changes in plants. Recent studies have shown that Ca could be used as an exogenous substance to protect plants against Cd stress by the alleviation of growth inhibition, regulation of metal uptake and translocation, improvement of photosynthesis, mitigation of oxidative damages and the control of signal transduction in the plants. The effects of Ca on toxic concentrations of Cd in plants are reviewed. This review also provides new insight that plants with enhanced Ca level have improved resistance to Cd stress.

Residual effects of monoammonium phosphate, gypsum and elemental sulfur on cadmium phytoavailability and translocation from soil to wheat in an effluent irrigated field

Cadmium (Cd) accumulation in agricultural soils is one of the major threats to food security. The application of inorganic amendments such as mono-ammonium phosphate (MAP), gypsum and elemental sulfur (S) could alleviate the negative effects of Cd in crops. However, their long-term residual effects on decreasing Cd uptake in latter crops remain unclear. A field that had previously been applied with treatments including control and 0.2, 0.4 and 0.8% by weight of each MAP, gypsum and S, and grown with wheat and rice and thereafter wheat in the rotation was selected for this study. Wheat (Triticum aestivum L.) was grown in the same field as the third crop without further application of amendments to evaluate the residual effects of the amendments on Cd uptake by wheat. Plants were harvested at maturity and grain, and straw yield along with Cd concentration in soil, straw, and grains was determined. The addition of MAP and gypsum significantly increased wheat growth and yield and decreased Cd accumulation in straw and grains compared to control while the reverse was found in S application. Both MAP and gypsum decreased AB-DTPA extractable Cd in soil while S increased the bioavailable Cd in soil. Both MAP and gypsum increased the Cd immobilization in the soil and S decreased Cd immobilization in a dose-additive manner. We conclude that MAP and gypsum had a significant residual effect on decreasing Cd uptake in wheat. The cost-benefit ratio revealed that gypsum is an effective amendment for decreasing Cd concentration in plants.