Cd Concentrations In Roots Research Articles

Migration and transformation of cadmium in rice - soil under different nitrogen sources in polymetallic sulfide mining areas

We conducted pot experiments to assess the bioavailability of cadmium (Cd) in contaminated rhizosphere soil and accumulation in rice organs in response to nitrogen (N) supply ((NH4)2SO4, NH4NO3, NH4Cl). The results showed that the concentration of bioavailable Cd in rice rhizosphere soil was (NH4)2SO4 treatment > NH4Cl treatment > NH4NO3 treatment at the same level of N application and growth period; the Cd concentration in rice roots was (NH4)2SO4 treatment > NH4NO3 treatment > NH4Cl treatment; and the Cd concentration in rice straw was NH4NO3 treatment > NH4Cl. The Cd concentration in rice roots, straws, and seeds at the maturity stage was (NH4)2SO4 treatment > NH4Cl treatment. With the same N fertilizer, excessive N promoted Cd accumulation in rice at later growth stages. This suggested that sulfate (SO42−) influenced Cd concentration in rice. NH4Cl application maintained a low Cd level in different rice organs with the same N level. This confirmed that NH4Cl is a safe N source for rice planting in polymetallic sulfide mining areas. The study concludes that appropriate NH4Cl levels for Cd-contaminated paddy soil with high-S-content could obtain rice grains with Cd concentrations below the food safety standards (0.2 or 0.4 mg·kg−1).

Tolerance Mechanism and Cadmium Enrichment Abilities in Two Brassica napus L. Cultivars

A hydroponic experiment was conducted to explore the differences in growth status and Cd accumulation characteristics of two Brassica napus L. cultivars (QY-1 and SYH) under different concentrations of cadmium (Cd) stress (0, 2, and 5 mg·L-1). The Cd subcellular compartmentalization and antioxidant enzyme activities were determined to elucidate the intrinsic mechanism of the differences in the Cd accumulation capacity between the two cultivars of Brassica napus L. Furthermore, field trials were conducted to further verify the differences in phytoremediation of the two cultivars. Results show that neither of the cultivars exhibited obvious growth inhibition under Cd stress. Under the 2 mg·L-1 Cd condition, there were no significant differences in shoot Cd concentrations between the two cultivars. Under 5 mg·L-1 Cd condition, however, the Cd concentrations in both shoot and root of SYH were significantly higher than that of QY-1, which increased by 32.05% and 99.57%, respectively. In addition, the bioconcentration factor (BCF) of the root in SYH is significantly higher than that of QY-1. The subcellular Cd distribution in leaves of the two cultivars of Brassica napus L. showed that, with an increase of Cd stress, Cd concentrations of heat stable protein (HSP) and metal-rich granule (MRG) fractions in leaves significantly increased by 143.69% and 118.91% for QY-1, and by 63.34% and 118.91% for SYH. Thus, the segregation of Cd in HSP and MRG, which was reported to be biological detoxified metal fractions (BDM), might play an important role in the detoxification of Brassica napus L. at a subcellular level under Cd stress. Moreover, the distribution of Cd in the cellular debris fraction might be another important factor contributing to the differences in Cd accumulation of the two Brassica napus L. cultivars, which was 4.41 times higher in SYH than in QY-1 under Cd stress. The results of the antioxidant enzyme activities of two Brassica napus L. cultivars showed that, under the 5 mg·L-1 Cd condition, the antioxidant enzyme system may represent an important detoxification mechanism for QY-1 to cope with stress induced by high concentrations of Cd, while SYH is more effective in reducing the toxicity of Cd by separation of Cd into BDM fractions. The results of the field trial confirmed that the Cd concentrations in the above- and underground parts of SYH were 2.34 and 1.43 times higher than in QY-1, respectively. Therefore, SYH possess a higher Cd phytoextraction capacity than QY-1, and might be a good candidate for the remediation of moderate and mildly Cd-contaminated farmland.

Heavy metal concentrations in roadside plants (Achillea wilhelmsii and Cardaria draba) and soils along some highways in Hamedan, west of Iran.

The present study was conducted to analyze the effects of traffic volumes on Cd, Cu, Pb, Ni, and Zn contents in roadside soils and in two dominant herbaceous species (Achillea wilhelmsii and Cardaria draba) along highways and to evaluate the dynamic characteristics of these elements and their accumulation by the aerial parts and roots of these herbaceous species. The plant samples were collected along 700m of a 9-km segment of each of the three major highways in Hamedan Province (West Iran) with different traffic volumes: Hamedan-Goltapeh (HG), Hamedan-Razan (HR), and Hamedan-Kermanshah (HK). The results indicated that the mean contents of Cd, Cu, Pb, Ni, and Zn in the soil samples were 0.26, 18.74, 14.98, 18.21, and 62.25mgkg-1, respectively. Furthermore, the mean contents of elements (mgkg-1) in aerial parts of A. wilhelmsii were 0.16 for Cd, 4.52 for Cu, 1.91 for Pb, 1.70 for Ni, and 44.80 for Zn, while in the aerial part samples of C. draba, the concentrations (mgkg-1) and the mean contents were 0.16, 2.29, 2.58, 1.60, and 31.29, respectively. This meant that the traffic volume affected the contents of the metals in the soil and the herbaceous species. The metal content in herbaceous tissues varied significantly between plant species. A. wilhelmsii tended to accumulate the metals in the roots while C. draba retained them mostly in the aerial parts. The significant positive correlations of Cd, Cu, Ni, and Zn content in root and aerial parts of the herbaceous plant with those found in the soil samples showed the potential of the studied species for application in biomonitoring studies. Comprehensive analysis (effect of traffic volumes and relationships between the content of elements in plant tissues and soil samples) indicated that Cu in both herbaceous plants was mainly derived from soil, while A. wilhelmsii absorbed Cd and C. draba absorbed Zn mainly through the stomata from atmospheric depositions. Without considering atmospheric depositions due to intense traffic volumes, in A. wilhelmsii, the translocation factor (TF) values of Cu and Zn were 1.06 and 1.44, respectively and in C. draba, the TF values of Cd, Cu, and Pb were 1.06, 1.09, and 1.13, respectively, thus suggesting that both herbaceous species had high potentials for transferring metals from the roots to aerial parts.

Effects of root exudation on the accumulation of Cd by Chenopodium ambrosioides L. and maize in intercropping systems

Pot experiments were carried out to study the effects of intercropping by Chenopodium ambrosioides L. and maize on the root exudates of soluble sugar and amino acids, in order to understand the relationship between root exudates and cadmium accumulation in plants. The results showed that, compared with monoculture system: (1) after intercropping with maize, the content of soluble sugar in root exudates of C. ambrosioides increased by 106.54%, the content of amino acids increased by 52.73%, the available Cd content in rhizosphere soil increased by 12.09%, the root Cd content increased by 15.52%. (2) The content of soluble sugar in root exudates of maize increased by 40.41%, the content of amino acids increased by 70.59%, the available Cd content in rhizosphere soil increased by 29.35%, the shoot Cd content of maize increased by 208.26%. (3) There were significantly posotive correlations between the contents of soluble sugar and amino acids secreted by C. ambrosioides and maize roots and the available Cd content in soil. In addition, there was a significant positive correlation between the available Cd content in soil and the Cd contents in the shoots and roots of plants. The results showed that the increase of soluble sugar and amino acid content of root exudates under the intercropping system caused the change of the available Cd content in the rhizosphere soil, which eventually changed the accumulation of Cd in the shoot and root of C. ambrosioides and maize.

Cadmium toxicity in cowpea plant: Effect of foliar intervention of nano-TiO2 on tissue Cd bioaccumulation, stress enzymes and potential dietary health risk

The study was conducted to investigate the effects of foliar-intervention of nano-TiO2 on Cd toxicity in cowpea plants. Cowpea plants were exposed to Cd toxicity at 10 mg/kg soil for 21 days and afterwards, subjected to six episodes of foliar application of nano-TiO2 intervention. Results showed that foliar-applied nano-TiO2 significantly promoted chlorophyll b and total chlorophyll contents after Cd stress as compared to Cd-stressed plants without the intervention. Interestingly, Cd contents of roots, shoots and grains were significantly reduced (p < 0.05) after nano-TiO2 sprays compared to Cd-stressed plants. However, the Cd contents in edible tissues (leaves and seeds) after interventions remained above recommended threshold. Furthermore, nano-TiO2 interventions promoted stress enzymes activity in both roots and leaves as well as increased Zn, Mn and Co levels in seeds compared to Cd-stressed plants without intervention. Estimated daily intake of Cd in leaves and seeds for adult subpopulation exceeded the WHO recommended daily intake by some folds in Cd-stressed and nano-TiO2-treated plants. The health risk quotient (HQ) for adult subpopulation exceeded unitary in seeds from nano-TiO2 treatments (HQ = 1.75 and 1.96, respectively) while no potential risk was obtained for leaves. Overall, foliar application of nano-TiO2 portends significant ameliorative potential for Cd toxicity in cowpea plants.

Selenium mitigates cadmium toxicity by preventing oxidative stress and enhancing photosynthesis and micronutrient availability on radish (Raphanus sativus L.) cv. Cherry Belle.

We aimed to examine the effects of selenium on the tolerance of radish plants CV. Cherri Belle under cadmium phytotoxicity. The biomass accumulation was drastically decreased under Cd toxicity and the supplementary Se maintained the biomass acquisition under Cd pressure. The chlorophyll index (SPAD), PSII efficiency (Fv/Fm), and PSII quantum yield (ΦPSII) were declined in response to Cd treatment, while Se nutrition improved these variables in a dose-dependent manner. The highest H2O2 and MDA contents were observed in the plants fed with 10mg-1L Cd. The Cd stress resulted in a considerable decline in the activities of GPX, CAT, and APX antioxidant enzymes, while Se supplementation increased their activities in the Cd-treated plants. Based on the mineral analyses, no Cd was traced in the control plants, while the Cd concentration in both roots and leaves of the Cd-stressed radish plants increased with increasing the supplemented Cd levels. Compared with plants solely treated with 10mgL-1 Cd, Se nutrition declined the Cd absorption in roots and in leaves. The concentration of evaluated micronutrients including Fe, Mn, Cu, and Zn tended to decrease in the Cd-imposed plants in comparison with control plants. Se nutrition of both stressed and non-stressed radish plants increased the concentrations of the studied microelements, except for Zn in which the individual use of Se led to a decrease in the Zn content. Significant positive and negative correlation values were found among the studied traits and the principle component analysis (PCA) biplot and Ward dendrogram confirmed the results of the correlation analysis. Se proved to be efficient in the alleviation of Cd-triggered deleterious effects by improving biomass acquisition, enhancing chlorophyll biosynthesis and fluorescence, and increasing micronutrient uptake in a dose-dependent manner. Furthermore, the Se alleviation mechanism under Cd stress was also connected with the activation of enzymatic antioxidative protection system as well as with decreasing Cd uptake, transport, and distribution in radish leaves. Altogether, our research strongly suggests the implementation of Se in the growth medium to enhance the tolerance of radish plants under Cd stress.

Isolation, characterization and inoculation of Cd tolerant rice endophytes and their impacts on rice under Cd contaminated environment

Cadmium (Cd) contamination in paddy soil becomes increasingly prominent in recent years, which endangers the safe production of food crops. Cd-tolerant endophytes are ideal mediators for decreasing Cd content in rice plants, but their effects on the rice endophytic microbial community and gene expression profile have not yet been well elucidated. In this study, 58 endophytic bacteria from rice seeds were isolated and characterized. Five strains of them were selected based on their potential growth-promoting traits and strong Cd tolerance that could grow well under 4 mM Cd2+. By 16S ribosomal RNA (rRNA) identification, these five strains were designated as Enterobacter tabaci R2-7, Pantoea agglomerans R3-3, Stenotrophomonas maltophilia R5-5, Sphingomonas sanguinis R7-3 and Enterobacter tabaci R3-2. Pot experiments in relieving Cd stress in rice plants showed that the S. maltophilia R5-5 performed the strongest potential for reducing the Cd content in root and blade by 81.33% and 77.78%, respectively. The endophytic microbial community diversity, richness and composition were significantly altered in S. maltophilia R5-5 inoculated rice plants. Reverse-transcription qPCR (RT-qPCR) showed that the expression of Cd transporters, OsNramp5 and OsHMA2, were down-regulated in S. maltophilia R5-5-innoculated rice roots. The results indicate that the inoculation of endophytic bacteria S. maltophilia R5-5 provides a reference for alleviating the heavy metal contamination in paddy fields and can be a better alternative for guaranteeing the safe production of crops. Changes in the relative abundance of Cd-resistant microorganisms and the expression of Cd transporters might be the intrinsic factors affecting cadmium content in rice.

The sweet side of misbalanced nutrients in cadmium‐stressed plants

AbstractSome plants are able to maintain or improve their performance under cadmium (Cd) exposure, despite high Cd concentrations in roots and shoots, indicating that they have protective strategies to neutralise the side effects from Cd accumulation. The regulation of antioxidant machinery and the mitigation of Cd uptake and translocation have been the focus of several studies, but evidence shows that the modulation of nutritional status is also involved in tolerance mechanisms. Although alterations in the nutrient concentrations are usually coupled to negative outcomes on the development of plants under Cd exposure, current works have shown their “sweet” sides. Here, we provide evidence that the degree of plant tolerance to short Cd exposure is, at least partially, associated with differential changes in magnesium (Mg), manganese (Mn) and boron (B) status, all of which modulate physiological and developmental events, such as root architecture (Mg and/or B status), ionomic balance (Mn and/or B status), biomass production (Mg and/or Mn status) and biomass allocation (Mg/K ratio). Modulation of root architecture can be a strategy to obtain water and nutrients in metal‐free patches in a growing medium. Changes in the uptake and/or distribution of nutrients may adjust the ionomic profile to equilibrate charge and pH homeostasis after Cd entrance into the plant. Alterations in the Mn and Mg status may alter the balance between photorespiratory and photosynthetic metabolisms. Finally, reprogramming biomass allocation among organs can be a strategy to remodelling plant body in order to better cope with environmental challenges. The identification and understanding of plant tolerance mechanisms against heavy metal toxicity is necessary to support strategies to mitigate their impacts on crop productivity and quality, supporting food security in increasing environmental contamination in the Anthropocene.

Arbuscular mycorrhizal fungi and organic manure have synergistic effects on Trifolium repens in Cd-contaminated sterilized soil but not in natural soil

The objective of this study was to examine the effects of arbuscular mycorrhizal fungi (AMF) and organic manure on the growth and element uptake of Trifolium repens and the soil chemical and biological characteristics in sterilized and natural soils. An increase in organic manure input reduced mycorrhizal colonization in the sterilized soil treatment. In comparison to the treatments in which AMF inoculation did not occur, AMF inoculation significantly promoted the biomass of shoots and roots in the sterilized soil at the 2.5 and 5% organic manure incorporation levels, whereas AMF had no effect on biomass in the natural soil. Regardless of soil type and whether AMF inoculation occurred, the N, P, K and Mg concentrations of the shoots and roots and the Cd concentration of the roots were increased by organic manure amendment. In comparison to the 2.5% organic manure amendment treatment, the addition of 5% organic manure to the sterilized soil decreased the N, P, K, Ca and Cd contents in the absence of AMF but had no negative effect on the N, P, K, Mg and Cd contents in the presence of AMF. The soil available P, pH, microbial biomass carbon, microbial biomass nitrogen, dissolved organic carbon, diethylenetriamine pentaacetic acid (DTPA)-extractable Cd and root Cd concentrations increased with increasing organic manure input. These results indicate that additive effects of AMF inoculation and organic manure on the growth and nutrient contents of Trifolium repens occurred in the Cd-contaminated sterilized soil but not in the natural soil, implying the limited function of nonnative AMF introduced into natural soils.

Remediation of Cd-contaminated soils by GWC application, evaluated in terms of Cd immobilization, enzyme activities, and pakchoi cabbage uptake.

Compost (mainly composed of cow manure, horse manure, chicken manure, and straw) has turned out to be effective in remediation of heavy metal-contaminated soil. However, in recent years, the effects of green waste compost (GWC) on plant growth and the immobilization of heavy metal cadmium (Cd) in the soil have not been clearly studied. We considered the effects of different GWC ratios on the growth of pakchoi cabbage, soil physical and chemical properties, total and availability of Cd content, and soil enzyme activity. The results showed that organic matter, total nitrogen, available phosphorus, and available potassium in the soil gradually put in place over the increase of compost proportion and showed a significant difference. Dehydrogenase, urease, and catalase activities grew by 380, 35, and 32% under the treatment of T10, respectively. The increase of enzyme activity indirectly reflects the enhancement of self-purification ability of contaminated soil. The addition of GWC improved soil quality, leading to a significant increase in soil nutrients, and in biomass and chlorophyll content of pakchoi cabbage. The decrease of Cd availability led to a significant reduction of Cd content in pakchoi cabbage, with a 30-36% reduction of Cd content in roots and a 43-69% reduction in leaf. The BCF of leaves decreased from 0.62 to 0.22, and the TF decreased from 0.94 to 0.46, indicating that the addition of GWC reduced the mobility of Cd to pakchoi cabbage leaves. The result is decreased in Cd content in edible parts of pakchoi cabbage.

Magnetic removal/immobilization of cadmium and zinc in contaminated soils using a magnetic microparticle solid chelator and its effect on rice cultivation

Magnetic removal techniques using functionalized magnetic nanoparticles as adsorbents have been frequently tested for use in the removal of heavy metals in aqueous solution, but seldom in farmland soil. Here, a novel magnetic microparticle solid chelator (MSC) was employed as the adsorbent for magnetic removal and/or immobilization of Cd and Zn in a paddy soil (PS), an upland soil (US), and a paddy–upland rotation soil (RS) with different degrees of pollution. MSC was applied to 14 kg air-dried soil samples (PS, US, and RS) at the dosage of 1% (w/w), and then watered, and intermittently stirred. Finally, the MSC–metal complexes were retrieved using a magnetic device (MCR treatment) or not (MC treatment), and the removal efficiency of soil Cd and Zn in MCR treatment was evaluated. After magnetic separation of MSC–metal complexes, pot experiments were performed to investigate the impacts of the magnetic remediation process on rice growth, the phytoavailability of soil Cd and Zn, and the accumulation of Cd and Zn in rice plants. The MCR treatment exhibited recovery rates of 55.4%, 49.6%, and 19.0% for MSC–metal complexes in PS, US, and RS, respectively, which brought about removal efficiencies of 2.2–12.2% for Cd and 1.9–4.6% for Zn. The MC and MCR treatments substantially decreased the availability of soil Cd, but not soil Zn; this effect was more remarkable when using CaCl2 instead of DTPA as the extractant for determination of bioavailable metals. Furthermore, the CaCl2-extractable Cd and Zn had a more significant relationship with Cd and Zn concentrations in rice roots. The MC and MCR treatments led to dramatic reductions in rice grain Cd of 23.9–72.1% and 37.3–63.9%, respectively, in the three soils relative to the respective controls. The MC and MCR treatments also exhibited an inhibitory effects on rice grain Zn accumulation in US (10.6% and 4.3% decreases, respectively) and RS (9.3% and 19.5% decreases, respectively), but not in PS. Moreover, the grain yield was unaffected under the MCR treatment in the three soils, and significantly increased by 29.8% under the MC treatment in US. Our study suggests that MSC-based magnetic remediation technique can effectively immobilize and/or remove Cd and Zn in farmland soils, decreasing their uptake by rice plants, with no adverse effects on grain yield.

Intercropping with Eclipta prostrata and Crassocephalum crepidioides decrease cadmium uptake of tomato seedlings

ABSTRACT Two pot experiments were conducted to study the effects of intercropping with cadmium (Cd) accumulator plant Eclipta prostrata and hyperaccumulator plant Crassocephalum crepidioides on the growth and Cd accumulation of tomato seedlings. In the preliminary experiment, intercropping with E. prostrata and C. crepidioides promoted the growth and decreased the Cd content in roots and shoots of tomato seedlings. In the further experiment, intercropping with E. prostrata and C. crepidioides had the same effects on the growth and Cd content of tomato seedlings as the preliminary experiment. In the further experiment, when three plant species (E. prostrate, C. crepidioides and tomato) intercropping together, the root and shoot biomasses of tomato seedlings got the maximum, and the Cd content in tomato seedlings got the minimum. Compared with the monoculture of tomato, three plant species intercropping increased the root and shoot biomasses of tomato seedlings by 49.28% and 64.19%, respectively, and decreased the Cd contents in roots and shoots of tomato seedlings by 17.35% and 22.35%, respectively. Intercropping with E. prostrata and C. crepidioides also increased the photosynthetic pigment content and enhanced the antioxidant enzyme activity of tomato seedlings. For accumulator and hyperaccumulator plants, intercropping with tomato inhibited the growth of E. prostrata and C. crepidioides, while increased the Cd content in two plant species. Therefore, intercropping with E. prostrata and C. crepidioides could promote the growth and reduce the Cd uptake of tomato seedlings, and three plant species intercropping together was the best combination.

Effects of mutual intercropping on cadmium accumulation in seedlings of three varieties of eggplant

ABSTRACT The aim of this study was to determine the effects of mutual intercropping on cadmium (Cd) accumulation in three different varieties of eggplant (Solanum melongena L.). Seedlings of three eggplant varieties (red, green and black) were intercropped with various combinations in Cd-contaminated soil and their Cd accumulation characteristics were compared. These three varieties of eggplant mutual intercropping treatments led to increased root, stem, leaf, and shoot biomasses of eggplant seedlings compared with their respective monocultures. The shoot biomasses of red, green, and black eggplant seedlings were 27.88%, 10.31%, and 6.06% higher in three-varieties intercropping treatment than in their respective monocultures. Mutual intercropping decreased the biomasses of different organs of green and black eggplant seedlings compared with their respective monocultures, and of red eggplant when intercropped with green eggplant, but increased those of red eggplant intercropped with black eggplant. The trends in photosynthetic pigment contents and antioxidant enzyme activity were similar to those of biomass. Mutual intercropping significantly decreased the Cd contents in roots of the three varieties of eggplant, but increased the Cd contents in their stems, leaves, and shoots. Intercropping of the three eggplant varieties increased the Cd contents in shoots of red, green, and black eggplants seedlings by 21.26%, 39.04%, and 4.87%, respectively, compared with their respective monocultures. Because mutual intercropping promotes the Cd absorption of eggplant seedlings in Cd-contaminated soil, it may not be a suitable cultivation strategy for eggplant in Cd-contaminated areas.

Effects of Different Amendments on Fractions and Uptake by Winter Wheat in Slightly Alkaline Soil Contaminated by Cadmium and Nickel

The effects of a single application of three amendments (biochar, lignite, and chicken manure) on the fraction transformations of soil Cd and Ni and uptake by winter wheat are reported to provide reference for passivation and the remediation of heavy metals in soil. Field experiments were conducted to investigate the effects of different passivators on the forms of Cd and Ni in soils at different growth stages of winter wheat, and to analyze the contents of Cd and Ni in different organs of wheat. The results showed that biochar increased soil pH and that lignite reduced soil pH, but not significantly. Chicken manure significantly reduced soil pH at booting and mature stages, and decreased by 0.23 and 0.20 pH units, respectively. The single application of biochar, chicken manure, or lignite did not reduce the exchangeable Ni content significantly, whereas the effect on the exchangeable Cd was significant. Lignite 2% treatment had the greatest decrease in exchangeable Cd at different growth stages of wheat, which were 30.50%, 43.34%, and 31.20%, respectively. The contents of Cd and Ni in the shoots and underground parts of wheat decreased to some extent, and the extent of these decreases increased with the increase of passivator dosage. The decrease of Cd content in wheat roots was the largest under the treatment of lignite 2% at different growth stages, reaching 38.35%, 58.00%, and 50.20% respectively. The greatest decline of Ni content in wheat roots occurred in the lignite 2% treatment at the booting (41.33% decline) and mature stages (51.35%). All the three amendments reduced the availability of Cd and Ni in slightly alkaline soil, and the passivation effect on Cd was better than that of Ni. All three amendments also effectively reduced the content of Cd and Ni in different organs of wheat plants in different growth period. The order of decreasing effect of Cd in wheat organs was lignite > biochar > chicken manure at the same dose of these three passivators.

Effects of external Mn2+ activities on OsNRAMP5 expression level and Cd accumulation in indica rice

Manganese (Mn) transporter OsNRAMP5 was widely reported to regulate cadmium (Cd) uptake in rice. However, the relationship between OsNRAMP5 expression level and Cd accumulation, impacts of external ion activities on OsNRAMP5 expression level and Cd accumulation are still unclear. Investigations of the relationship between OsNRAMP5 expression level and Cd accumulation in three indica rice genotypes were conducted under various external Mn2+ activities ranging from Mn deficiency to toxicity in EGTA-buffered nutrient solution. Results in this work indicated that OsNRAMP5 expression level in roots significantly up-regulated at Mn phytotoxicity compared to that at Mn deficiency, which may stimulate by the increasing uptake of Mn. Our work also demonstrated that root Cd concentration of all the tested rice decreased notably when external Mn2+ activity reached the level of toxicity. This may explain by the increasing competition between the excess Mn2+ and Cd2+ as well as the disorder of element absorption caused by root damage at Mn toxicity. Our work also revealed that the relationship between OsNRAMP5 expression level in roots and Cd accumulation in roots was insignificant for all the tested genotypes. Besides, OsNRAMP5 expression level in roots seemed more related to root Mn accumulation. The fact that function of OsNRAMP5 mainly focuses on Mn uptake, together with the fact that many transporter genes involved in Cd uptake might result in the insignificant correlation between OsNRAMP5 expression level and Cd accumulation in roots. At last, multi-level regulating and processing of the process from gene expression to protein translation might account for the inconsistent relationship between root OsNRAMP5 expression level and Cd accumulation in roots.

Geogenic cadmium pollution in multi-medians caused by black shales in Luzhai, Guangxi

Cadmium (Cd) concentration was investigated in parent rocks, surrounding soil of black shales outcrop, stream water, stream sediments, paddy soil as well as rice plants. Leaching test and sequential extraction procedure were applied to evaluate Cd mobility and bioavailability in soil samples. This study aims to emphasize ecological risk of Cd induced by black shales by combining various natural medias in black shales area and control area. The black shales parent rocks have elevated Cd concentration and act as a source of Cd. The liberated Cd from black shales outcrop temporarily accumulated in the acidized surrounding soil and could arise potential adverse impacts on environment due to rainfall. Although high concentration of Cd was not detected in stream water, Cd concentrated stream sediment was a hidden toxin for surface water system. Cd in paddy soil was primarily from geogenic source and effected little by anthropogenic source. The concentration as well as mobility and bioavailability of Cd were high in paddy soil in black shales area, which lead to elevated Cd concentration in roots, shoots and grains of rice. As a result, residents in black shales area suffer increased non-carcinogenic risk of Cd via food chain.

Insight into nitrogen and phosphorus enrichment on cadmium phytoextraction of hydroponically grown Salix matsudana Koidz cuttings

Cadmium (Cd) has already caused worldwide concern because of its high biotoxicity to human and plants. This study investigated how nitrogen (N) and phosphorus (P) enrichment alter the toxic morpho-physiological impacts of and accumulation of Cd in hydroponically grown Salix matsudana Koidz cuttings. Our results showed that Cd significantly depressed growth and induced a physiological response on S. matsudana cuttings, exhibiting by reduced biomass, decreased photosynthetic pigment concentrations, and increased soluble protein and peroxidase activity of shoots and roots. N and P enrichment alleviated the Cd toxic effects by increasing production of proline which prevented cuttings from damage by Cd-induced ROS, displaying with decreased malondialdehyde concentration, and stimulated overall Cd accumulation. Enrichment of N and P significantly decreased the upward Cd transfer, combing with enhanced root uptake (stimulated root activity) and retranslocation from stem, resulted in extensive Cd sequestration in S. matsudana roots. In both root and xylem, concentration of Cd is positively correlated withN and P. The improved phytoextraction potential by N and P enrichment was mainly via elevating Cd concentration in roots, probably by increased production of phytochelatins (e.g., proline) which form Cd chelates and help preventing damage from Cd-induced ROS. This study provides support for the application of S. matsudana in Cd phytoextraction even in eutrophic aquatic environments.

Effect of Plant Growth and Antioxidantive Enzyme Activity of Lettuce (Lactuca sativa L.var. longifolia) Applied to Cadmium and Zinc in Sewage Sludge Enriched with Soil

The aim of this study is to investigate the effects of a constant rate of sewage sludge (SS) together with cadmium (Cd) and zinc (Zn) at varying levels on the growth of lettuce and antioxidative enzyme activity. In the pot experiment, a fixed ratio of 10%SS with varying doses of Cd (Cd1:50 mg Cd kg-1; Cd2:100 mg Cd kg-1) and Zn (Zn1:250 mg Zn kg-1; Zn2:500 mg Zn kg-1) was applied. According to experiment results, compared to the control, 10% SS + Cd1 and 10% SS + Cd2 applications significantly reduced fresh and dry shoot weights, plant height, Zn content and SOD (superoxide dismutase) enzyme activity in the root and shoot of lettuce. However, 10%SS +Cd1 and 10%SS+Cd2 applications significantly increased shoot and root Cd contents, GPX (glutathione peroxidase) enzyme activity in plant and the amount of Cd in soil. On the other hand, 10%SS+Zn1+Cd1 application increased fresh shoot weight, Zn content, SOD and GPX enzyme activities in the shoot of lettuce and decreased the amount of DTPA-Cd in comparison with 10%SS+Cd1 application. Compared to the Cd1 application, 10%SS+Zn2+Cd1 application increased SOD and GPX enzyme activities in the root of lettuce. In comparison with 10%SS +Cd2 application, 10%SS+Zn2+Cd2 application increased fresh and dry shoot weight, Zn content, SOD and GPX enzymes in both shoot and root of lettuce and decreased shoot Cd content and the amount of DTPA-Cd in soil. These results indicate that the Zn application could be beneficial for reducing the toxic effects of Cd in lettuce.

Foliar application of selenium and zinc to alleviate wheat (Triticum aestivum L.) cadmium toxicity and uptake from cadmium-contaminated soil

Due to the large area of agricultural soils contaminated by Cd worldwide, cost-effective and practical method for safety food production are necessary. The roles of micronutrient on reducing Cd accumulation in crops are recently introduced. In the current study, a pot-culture experiment in the greenhouse was conducted to study the foliar spraying of Se (Na2SeO4) and Zn (ZnSO4) on physiological and growth parameters, as well as Cd concentrations in wheat plants grown in Cd-contaminated soil. The foliar was sprayed with four concentration of Se and Zn (0, 10, 20, and 40mgL-1) at different growth stage (tillering, elongating and heading) and whole wheat plants were collected after maturity. Both foliar spraying with Se and Zn significantly enhanced the photosynthesis, tissue biomass and antioxidant enzyme activity. Additionally, Se and Zn application can also increase Se and Zn concentrations in different plant tissues. Selenium and Zn decreased malondialdehyde (MDA) and Cd concentrations in wheat grains, hulks, leaves, stalks and root in a dose-additive manner. Overall, Se and Zn both efficiently enhanced the wheat growth and Se and Zn concentrations, and simultaneously decreased the Cd concentration in wheat plant. Compared with Zn, Se more efficiently improved wheat growth and reduced Cd concentration in the wheat in a Cd-contaminated soil. Present results suggest that use of foliar spraying, especially Se, could be a cost-effective strategy and could be recommended for remediation of light-or moderate-polluted soils contaminated by Cd.

Effects of silicon nanoparticles on growth and physiology of wheat in cadmium contaminated soil under different soil moisture levels.

Soil degradation with different stress conditions like accumulation of cadmium (Cd) contents in soil and drought stress has become one of the most dangerous issues that obstruct the sustainable agriculture production. Silicon nanoparticles (Si NPs) play beneficial roles in combating various biotic and abiotic stresses but their role under combined metal and drought stress is not studied. A pot study was designed to determine the effect of Si NPs on wheat (Triticum aestivum L.) growth and uptake of Cd grown in Cd contaminated soil with different water levels under ambient conditions. Four different levels of Si NPs (0, 25, 50, and 100 mg/kg) were applied in the soil before 1 week of wheat sowing and two water levels (70% and 35% soil water-holding capacity) were introduced after 50 days of seed sowing for the remaining growth period. The lowest biomass, yield, and photosynthesis were observed in the control plants while oxidative stress and the highest Cd concentrations in shoots, roots, and grains were observed in the control plants, and the drought stress further enhanced this effect on the plants. The Si NPs treatments improved the plant growth indicators and photosynthesis, and reduced the Cd concentrations in wheat tissues, especially in grains either without or with drought stress. The Si NPs reduced the oxidative stress in leaves as was indicated by the reduced production of hydrogen peroxide, electrolyte leakage, and malondialdehyde contents, and increase in superoxide dismutase and peroxidase activities. The improvement in wheat growth and a reduction in oxidative stress and Cd concentration in tissues were dependent on the levels of Si NPs and the effect was the highest with the highest level of NPs used.