Shoot Cd Concentrations Research Articles

Cadmium Accumulation Characteristics of Four Herbs

A pot-based experiment was conducted to study the Cd tolerance and accumulation characteristics of four invasive herbs (Galinsoga quadriradiata, Panicum dichotomiflorum, Setaria geniculata, and Lolium persicum) under exposures of 0 (T0), 5 (T5), 25 (T25), and 50 mg·kg-1 (T50) soil Cd concentrations to screen for potential Cd accumulators for phytoremediation. The results showed that the biomasses of both shoots and roots of G. quadriradiata had no significant changes compared to the control (T0) samples under all Cd treatments, whereas the biomass of the other three Poaceae species significantly decreased under the T25 or T50 treatment. The results indicate that G. quadriradiata had stronger Cd tolerance than the other three species. The Cd concentrations in the shoots and roots of the four herbs significantly increased with an increase in soil Cd concentrations, but the shoot bioconcentration factors (SBCF) of the four plant species significantly decreased under T5, T25, and T50 treatment. The SBCF of G. quadriradiata and P. dichotomiflorum were greater than 1 whereas those of S. geniculata and L. persicum were lower than 1. The translocation factors (TF) of G. quadriradiata were 0.93, 0.73, and 1.04 under T5, T25, and T50 treatment, respectively, which were significantly higher than those of the other three plants under the same soil Cd concentration. In addition, both the total Cd and shoot Cd contents of G. quadriradiata were notably higher than in the other three species under the same Cd treatment. Moreover, 90% of the Cd in G. quadriradiata could be transferred aboveground, which was significantly higher than for the other three plants. Based on our comprehensive comparison of Cd tolerance and accumulation capacity, we suggest that G. quadriradiata is a high-Cd accumulator with considerable phytoremediation potential.

Living plants and straws of four hyperaccumulator plants increase the cadmium uptake of Ziziphus acidojujuba seedlings

ABSTRACT The effects of living plants and straws of four hyperaccumulator plant species (Siegesbeckia orientalisL., Crassocephalum crepidioides, Galinsoga parviflora and Solanum nigrumL.) on the growth and cadmium (Cd) content of Ziziphus acidojujuba seedlings were studied through intercropping and straw-applying experiments. Compared to the control, the four hyperaccumulator plant species and their straws increased the biomass, photosynthetic pigment contents, antioxidant enzyme activities and soluble protein content of Z. acidojujuba seedlings. The growth of Z. acidojujuba seedlings was increased most significantly by intercropping with G. parviflora and applying S. orientalis straw. Two experiments both reduced Cd content in roots of Z. acidojujuba seedlings, while increased the Cd content in shoots of Z. acidojujuba seedlings. The Cd content in shoots of Z. acidojujuba seedlings increased most significantly when intercropping with G. parviflora and applying C. crepidioides straw. In summary, four living hyperaccumulator plant species and their straws promoted the growth of Z. acidojujuba seedlings while increased the Cd content of the shoots, an outcome not conducive to the remediation of Cd-contamination jujube orchards.

Enhancing cadmium extraction potential of Brassica napus: Effect of rhizosphere interactions

Brassica napus L. (oilseed rape) was grown with daikon and white lupin in a polyvinyl chloride split pot experiment (with no barrier between the compartments or by a nylon mesh barrier (37 μm) to license partial root interaction, or a solid barrier to stop any root interactions) to examine the effect of rhizosphere interaction on the cadmium uptake. The results showed that shoot and root biomasses of oilseed rape were 40.66% and 26.94% less than that of the monocropped treatment (solid barrier) when intercropping with daikon under the rhizosphere complete interaction. However, the intermingling of roots between oilseed rape and white lupin notably enhanced the dry biomass of oilseed rape by 40.23% and decreased with the reduction of root contact. Oilseed rape intercropping with daikon enhanced the shoot Cd concentration of oilseed rape. The shoot Cd concentration (44.8 mg/kg) of oilseed rape when intercropped white lupin under complete rhizosphere interaction were greater than those of other treatments. Additionally, the intermingling of roots played a positive role in the content of citric and malic acids when intercropping with white lupin. In all systems, the BCF values of oilseed rape >5. Therefore, intercropping with white lupin may contribute to higher biomass and increased uptake Cd by oilseed rape. We can toward sustainable positive effects on phytoremediation that based on a better understanding of rhizosphere processes.

Comparative morpho-physiological analyses revealed H2O2-Induced different cadmium accumulation in two wheat cultivars (Triticum aestivum L.)

Different wheat cultivars have their individual defense response to heavy metal stress, exploring which is beneficial to using targeted and effective agronomic practice to reduce cadmium (Cd) accumulation in plants. Our previous study shows Cd concentration is higher in the Cd-tolerant cultivar Bainong 160 than the sensitive one Pingan 8. In this experiment, Bainong 160 showed stronger Cd uptake capacity and lower Cd translocation than Pingan 8, leading to its higher Cd concentration in roots and shoots, as verified by both dose- and time-dependent experiments. This study aims at exploring the factors underpinning Cd resistance and accumulation in wheat, and whether there is an interaction between them. There was a positive correlation between Cd distribution in organelle and H2O2 concentration in both shoot (r = 0.7) and root (r = 0.94**), suggesting that the less Cd distribution in organelle of Bainong 160 contributes to its lower H2O2 concentration than Pingan 8. For Pingan 8, lower expression of TaNramp6 and Cd-induced programmed cell death in cortex lead to its weaker Cd uptake capacity; while for Bainong 160, there are stronger positive cellular responses to Cd stress, including severe lignification in cortex cell, casparian strip formation, increment of both GSH and phytochelatins, and significant increased expression of TaHMA3 and repressed expression of TaHMA2, which together result in its stronger Cd retention in root and so as to inhibit Cd root-to-shoot transfer. Correlation analysis shows most of these reactions are associated with H2O2 concentration. In conclusion, Cd stress induced higher H2O2 concentration in sensitive cultivar Pingan 8 than tolerant one Bainong 160. The excessive H2O2-associated passive reaction in sensitive cultivar caused its lower Cd uptake ability, and moderate H2O2-induced stronger active response in tolerant cultivar, promoting Cd retention in root.

Intercropping with post-grafting generation of Solanum photeinocarpum decreases cadmium accumulation in soybean (Glycine max)

A pot experiment was designed to explore the effects of different post-grafting generations of Solanum photeinocarpum Nakamura et Odashima intercropping on growth and cadmium (Cd) accumulation in soybeans (varieties: “Zaodou” and “Liaoxian”). Post generation of S. photeinocarpum (ungrafted, grafted on eggplant, potato, and tomato, respectively) were utilized to intercrop with two varieties of soybean in Cd-contaminated soil. Soybean monoculture was employed as a control. Consequently, intercropping with different post-grafting S. photeinocarpum generation, except for tomato rootstock grafts post-generation, could reduce soybean biomass and photosynthetic pigment content. Additionally, all S. photeinocarpum post-grafting generations had the capacity to reduce Cd content in soybean when intercropping, while tomato rootstock grafts post-generation exhibited an adequate ability to accumulate Cd in S. photeinocarpum compared to the ungrafted treatment. In particular, tomato rootstock grafts post-generation could effectively decrease Cd content in soybean organs by 14.09–62.13%, relative to soybean monoculture, but increased shoot Cd content and shoot Cd extraction of S. photeinocarpum by 10.33–13.49% and 10.38–12.03%, respectively, compared to the ungrafted treatment. Thus, tomato rootstock grafting may enhance the ability of post-grafting generation of S. photeinocarpum to remediate Cd-contaminated soil, and this grafting was able to reduce Cd accumulation in soybean.

Graphitic carbon nitride (g-C3N4) alleviates cadmium-induced phytotoxicity to rice (Oryza sativa L.).

In the present study, graphitic carbon nitride (g-C3N4) was synthesized in a tube furnace and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Different concentrations (0-200 mg/L) of g-C3N4 were prepared in nutrient solution amended with or without 20 mg/L CdCl2 for the greenhouse study. Rice seedlings were exposed to g-C3N4 and Cd for 20 days. Our results suggest that 200 mg/L g-C3N4 significantly increased the fresh weight and root and shoot length as compared with the control, and notably alleviated Cd-induced toxicity. The addition of 200 mg/L g-C3N4 significantly reduced the root and shoot Cd content by approximately 14% and 23%, respectively. In addition, 200 mg/L g-C3N4 significantly elevated the nitrogen content and decreased C/N ration in rice shoots; most importantly, it alleviated Cd-induced nitrogen reduction. Our findings demonstrated the potential of g-C3N4 in regulating plant growth and minimizing the Cd-induced phytotoxicity, and shed light on providing a new strategy to maintain heavy metal contamination in agriculture using a low-cost and environmental friendly NMs.

Effects of UV-modified biochar derived from phytoremediation residue on Cd bioavailability and uptake in Coriandrum sativum L. in a Cd-contaminated soil.

Biochar has been applied widely as an amendment in the remediation of contaminated soil to immobilize the heavy metals. However, the role of ultraviolet (UV) irradiation modified biochar derived from the residues of phytoremediation plants in the contaminated soil not investigated yet. In this study, the UV-modified biochars were obtained from Brassica napus L. and Lolium perenne L. by pyrolysis at 600 °C. They were applied in a pot experiment to investigate their effect on Cd bioavailability and uptake in Coriandrum sativum L. in a Cd-contaminated soil at four addition rate (0%, 0.2%, 0.4%, and 0.6%). The results showed that the Cd was effectively stabilized in the biochar with environmentally acceptable leaching toxicity. The specific surface area and carboxyl functional group of biochar were greatly increased after UV modification. The application of biochar progressively increased the soil pH and electrical conductivity (EC). Furthermore, the CaCl2-extractable Cd was significantly reduced by 18.4-51.4% with biochar amendments. The concentration of Cd in shoots and roots was significantly reduced by biochars. In conclusion, the UV-modified biochar obtained from phytoremediation residue could effectively deal with hazardous waste and repair Cd-contaminated soil.

Cadmium, silicon and nutrient accumulation by maize plants grown on a contaminated soil amended with a diatomaceous Earth fertilizer

ABSTRACT: Given that cadmium (Cd) poses high persistence in the environment and toxicity to humans, strategies to either decrease or avoid Cd entry in the trophic chain are fundamental to secure food safety. Here we assessed the effects of applying rates of Si as a diatomaceous Earth-based fertilizer on the amelioration of Cd toxicity towards maize plants grown on soil with or without pH correction. Besides determining Si and Cd concentrations, we also evaluated plant accumulation of nutrients (N, P, K, Ca, Mg, Fe, Mn, Cu, and Zn) as a function of Si doses applied to the soil. Results showed that both the Si application and the liming had a positive effect on biomass and nutrient uptake, but the Si effect on plants’ performance took place irrespectively to the soil pH. Silicon ameliorated Cd phytotoxicity in both limed and unlimed soils by decreasing Cd concentration in shoots and improving biomass yield and plant nutrition. Silicon alleviation of Cd-inhibitory effects on plants was more effective in the unlimed soil owing to the higher Cd availability in acidic soils. Also, taking into account the reduced transfer of Cd to shoots driven by Si, lower Cd accumulation in maize grains is likely, with implications to food safety. So, further studies on field conditions are warranted.

Identification and characterization of SaeIF1 from the eukaryotic translation factor SUI1 family in cadmium hyperaccumulator Sedum alfredii.

Cadmium-sensitive yeast screening resulted in the isolation of protein translation factor SaeIF1 from the hyperaccumulator Sedum alfredii which has both general and special regulatory roles in controlling cadmium accumulation. The hyperaccumulator of Sedum alfredii has the extraordinary ability to hyperaccumulate cadmium (Cd) in shoots. To investigate its underlying molecular mechanisms of Cd hyperaccumulation, a cDNA library was generated from leaf tissues of S. alfredii. SaeIF1, belonging to the eukaryotic protein translation factor SUI1 family, was identified by screening Cd-sensitive yeast transformants with this library. The full-length cDNA of SaeIF1 has 582bp and encodes a predicted protein with 120 amino acids. Transient expression assays showed subcellular localization of SaeIF1 in the cytoplasm. SaeIF1 was constitutively and highly expressed in roots and shoots of the hyperaccumulator of S. alfredii, while its transcript levels showed over 100-fold higher expression in the hyperaccumulator of S. alfredii relative to the tissues of a nonhyperaccumulating ecotype of S. alfredii. However, the overexpression of SaeIF1 in yeast cells increased Cd accumulation, but conferred more Cd sensitivity. Transgenic Arabidopsis thaliana expressing SaeIF1 accumulated more Cd in roots and shoots without changes in the ratio of Cd content in shoots and roots, but were more sensitive to Cd stress than wild type. Both special and general roles of SaeIF1 in Cd uptake, transportation, and detoxification are discussed, and might be responsible for the hyperaccumulation characteristics of S. alfredii.

Abscisic acid utilizing rhizobacteria disturb nitrogen-fixing symbiosis of pea <em>Pisum sativum</em> L.

Rhizosphere bacteria are capable of utilizing various phytohormones (particularly auxins) as nutrients and thereby affect plant growth, nutrition and interactions with symbiotic microorganisms. Here, for the first time we evaluated the effects of rhizosphere bacteria Novosphingobium sp. P6W and Rhodococcus sp. P1Y capable of utilizing abscisic acid (ABA) on growth and nitrogen-fixing symbiosis of pea (Pisum sativum L.) line SGE and its Cd-insensitive mutant SGECdt using hydroponic culture. The plants were co-inoculated with the ABA-utilizing bacteria and nodule bacterium Rhizobium leguminosarum bv. viciae RCAM1066. Treatment with cadmium (Cd) was applied as an inducer of ABA biosynthesis in plants. In the presence of only nodule bacteria, Cd significantly inhibited the growth of roots and shoots and also decreased the nodule number and nitrogen-fixing activity in SGE peas, but not in the SGECdt mutant. Inoculation with ABA-utilizing bacteria also inhibited biomass production, nodulation and nitrogen-fixation of Cd-untreated SGE plants. This negative effect of bacteria on the SGECdt mutant was less pronounced. Contrary to this, ABA-utilizing bacteria had no effect on SGE plants treated with Cd, but decreased shoot biomass and nitrogen-fixing activity of the SGECdt mutant. Inoculation with ABA-utilizing bacteria had no effect on shoot Cd and nutrient content of both pea genotypes, suggesting that bacterial effects on plants were not associated with the plant nutrient status. We propose that the bacteria counteracted the increased ABA concentrations in SGE roots caused by Cd due to utilization of this phytohormone. However, opposite processes aimed at inhibiting and stimulating growth and legume–rhizobia symbiosis can be caused by the ABA-utilizing bacteria.

Overexpression of tomato RING E3 ubiquitin ligase gene SlRING1 confers cadmium tolerance by attenuating cadmium accumulation and oxidative stress.

Heavy metal pollution not only decreases crop yield and quality, but also affects human health via the food chain. Ubiquitination-dependent protein degradation is involved in plant growth, development, and environmental interaction, but the functions of ubiquitin-ligase (E3) genes are largely unknown in tomato (Solanum lycopersicum L.). Here, we functionally characterized a RING E3 ligase gene, SlRING1, which positively regulates cadmium (Cd) tolerance in tomato plants. An in vitro ubiquitination experiment shows that SlRING1 has E3 ubiquitin ligase activity. The determination of the subcellular localization reveals that SlRING1 is localized at both the plasma membrane and the nucleus. Overexpression of SlRING1 in tomato increased the chlorophyll content, the net photosynthetic rate, and the maximal photochemical efficiency of photosystem II (Fv/Fm), but reduced the levels of reactive oxygen species and relative electrolyte leakage under Cd stress. Moreover, SlRING1 overexpression increased the transcript levels of CATALASE (CAT), DEHYDROASCORBATE REDUCTASE (DHAR), MONODEHYDROASCORBATE REDUCTASE (MDHAR), GLUTATHIONE (GSH1), and PHYTOCHELATIN SYNTHASE (PCS), which contribute to the antioxidant and detoxification system. Crucially, SlRING1 overexpression also reduced the concentrations of Cd in both shoots and roots. Thus, SlRING1-overexpression-induced enhanced tolerance to Cd is ascribed to reduced Cd accumulation and alleviated oxidative stress. Our findings suggest that SlRING1 is a positive regulator of Cd tolerance, which can be a potential breeding target for improving heavy metal tolerance in horticultural crops.

Enhanced vacuole compartmentalization of cadmium in root cells contributes to glutathione-induced reduction of cadmium translocation from roots to shoots in pakchoi (Brassica chinensis L.)

Our previous studies showed that exogenous glutathione (GSH) decreased cadmium (Cd) concentration in shoots and alleviated the growth inhibition in pakchoi (Brassica chinensis L.) under Cd stress. Nevertheless, it is largely unknown how GSH decreases Cd accumulation in edible parts of pakchoi. This experiment mainly explored the mechanisms of GSH-induced reduction of Cd accumulation in shoot of pakchoi. The results showed that compared with sole Cd treatment, Cd + GSH treatment remarkably increased the expression of BcIRT1 and BcIRT2, and further enhanced the concentrations of Cd and Fe in root. By contrast, GSH application declined the concentration of Cd in the xylem sap. However, these results were not caused by xylem loading process because the expression of BcHMA2 and BcHMA4 had not significant difference between sole Cd treatment and Cd + GSH treatment. In addition, exogenous GSH significantly enhanced the expression of BcPCS1 and promoted the synthesis of PC2, PC3 and PC4 under Cd stress. At the same time, exogenous GSH also significantly improved the expression of BcABCC1 and BcABCC2 in the roots of seedling under Cd stress, suggesting that more PCs-Cd complexes may be sequestrated into vacuoles by ABCC1 and ABCC2 transporters. The results showed that exogenous GSH could up-regulate the expression of BcIRT1/2 to increase the Cd accumulation in root, and the improvement of PCs contents and the expression of BcABCC1/2 enhanced the compartmentalization of Cd in root vacuole of pakchoi under Cd stress. To sum up, exogenous GSH reduce the concentration of free Cd2+ in the cytoplast of root cells and then dropped the loading of Cd into the xylem, which eventually given rise to the reduction of Cd accumulation in edible portion of pakchoi.

Effects of Soil Amendments on Heavy Metal Immobilization and Accumulation by Maize Grown in a Multiple-Metal-Contaminated Soil and Their Potential for Safe Crop Production.

Soil amendments have been proposed for immobilizing metallic contaminants, thus reducing their uptake by plants. For the safe production of crops in contaminated soil, there is a need to select suitable amendments that can mitigate heavy metal uptake and enhance crop yield. The present experiment compared the effects of three amendments, hydroxyapatite (HAP), organic manure (OM), and biochar (BC), on plant growth and heavy metal accumulation by maize in an acidic soil contaminated with Cd, Pb, and Zn, and their potential for safe crop production. Toxicity characteristic leaching procedure (TCLP) tests, energy dispersive X-ray spectroscopy (EDS) analysis, and X-ray diffraction (XRD) analysis were used to evaluate the effectiveness and mechanisms of heavy metal immobilization by the amendments. The results showed that shoot and root biomass was significantly increased by HAP and 1% OM, with an order of 1% HAP > 0.1% HAP > 1% OM, but not changed by 0.1% OM and BC (0.1% and 1%). HAP significantly decreased Cd, Pb, and Zn concentrations in both shoots and roots, and the effects were more pronounced at the higher doses. OM decreased the shoot Cd and Pb concentrations and root Zn concentrations, but only 1% OM decreased the shoot Zn and root Pb concentrations. BC decreased the shoot Cd and Pb concentrations, but decreased the shoot Zn and root Pb concentrations only at 1%. HAP decreased the translocation factors (TFs) of Cd, Pb, and Zn (except at the 0.1% dose). OM and BC decreased the TFs of Cd and Zn, respectively, at the 1% dose but showed no significant effects in other cases. Overall, plant P, K, Fe, and Cu nutrition was improved by HAP and 1% OM, but not by 0.1 OM and BC. Soil pH was significantly increased by HAP, 1% OM, and 1% BC, following an order of 1% HAP > 1% OM > 0.1% HAP > 1% BC. The TCLP levels for Cd, Pb, and Zn were significantly reduced by HAP, which can be partly attributed to its liming effects and the formation of sparingly soluble Cd-, Pb-, and Zn-P-containing minerals in the HAP-amended soils. To some extent, all the amendments positively influenced plant and soil traits, but HAP was the optimal one for stabilizing heavy metals, reducing heavy metal uptake, and promoting plant growth in the contaminated soil, suggesting its potential for safe crop production.

Effects of Intercropping of Brassica chinenesis L. and Tagetes patula L. on the Growth and Cadmium Accumulation of Plants

A pot experiment was conducted to reveal the effects of intercropping a low-cadmium (Cd) accumulating cultivar and a Cd hyperaccumulator on the safe utilization and phytoextraction of Cd-polluted soils. Two cultivars of Brassica chinensis L. (the low-Cd accumulating cultivar Huajun, and the common cultivar Hanlü), were intercropped with four cultivars of Tagetes patula L. (Dwarf Red, Dwarf Yellow, Tall Red, and Tall Yellow). We examined the biomass, photosynthetic characteristics, and Cd accumulation in the plants and available Cd content and dissolved organic carbon (DOC) content in the soils. The results show that under the intercropping treatments, the biomass of B. chinensis decreased significantly and those of T. patula increased significantly, compared with the monoculture treatments. When intercropped with T. patula, the net photosynthetic rate, stomatal conductance, and transpiration rate in the leaves of B. chinensis decreased significantly, compared with the monoculture treatments. When Huajun was intercropped with Dwarf Red, the shoot Cd content of Huajun significantly decreased by 14.5%, and that of Dwarf Red increased significantly by 36.5% compared with the monoculture. Under the other intercropping treatments, the shoot Cd content of B. chinensis increased significantly, or showed no significant change, and that of T. patula showed no significant change. Under the intercropping treatments, the total amount of Cd in the shoot of B. chinensis decreased significantly, and that of T. patula increased significantly, compared with the monoculture. There were no significant differences in the Cd extraction ratios between the intercropping treatments and the monoculture of T. patula. The shoot Cd content of B. chinensis was significantly correlated with soil available Cd content and DOC content (P<0.01 and P<0.05, respectively). In conclusion, the intercropping treatment of Huajun and Dwarf Red significantly reduced shoot Cd content in B. chinensis and increased that in T. patula, and it did not affect the Cd extraction ratio. This is suitable for the safe utilization and phytoextraction of Cd-polluted soils.

Rhizosphere iron and manganese-oxidizing bacteria stimulate root iron plaque formation and regulate Cd uptake of rice plants (Oryza sativa L.)

Iron plaque is the amorphous and/or crystalline layer of Fe and Mn (hydr)oxides formed on the root surface of wetland plants. It could adsorb and co-precipitate metal(loid)s at the rhizosphere, thus modulating the uptake and accumulation of metal elements in plants. In this study, the Fe(II)/Mn(II)-oxidizing bacteria Burkholderia sp. D416 (D416) and Pseudomonas sp. YGL (YGL) were isolated from Cd-contaminated rice field, both hydroponic experiment and pot experiment were performed to assess the impact of bacterial inoculation on iron plaque formation, elemental content of the plaque, plant dry mass, antioxidant enzyme activity and Cd content in rice plants. The results revealed that inoculation with D416, YGL, and D416+YGL stimulated iron plaque formation on the root surface of the hydroponic rice. The content of C, N, O, Na, Mg, Al, Si, P, S, Cl, K, Fe and Ca in the root plaque were affected by the bacterial inoculation and varied among different plant growth stages. The pot experiment indicated that inoculation with D416 increased the root dry biomass by 58.89%, and the combined inoculation of D416 and YGL increased the dry biomass of root, shoot and grain by 16.89%, 21.66% and 23.26%, respectively. Importantly, YGL inoculation decreased the Cd translocation from root to shoot and from glume to brown rice grain by 50.00% and 50.27%, respectively, and the Cd content in shoot and brown rice grain were decreased by 20.00% and 34.48%, respectively. Taken together, the elemental content of the iron plaque and Cd content in rice plants varied among different plant growth stages and when plants were inoculated with different bacterial strains. YGL dramatically reduced the Cd content in brown rice grain, thus it could potentially be used to reduce Cd content in rice crop grown in Cd-contaminated soils.

Screening of Native Plants Growing on a Pb/Zn Mining Area in Eastern Morocco: Perspectives for Phytoremediation.

Screening of native plant species from mining sites can lead to identify suitable plants for phytoremediation approaches. In this study, we assayed heavy metals tolerance and accumulation in native and dominant plants growing on abandoned Pb/Zn mining site in eastern Morocco. Soil samples and native plants were collected and analyzed for As, Cd, Cu, Ni, Sb, Pb, and Zn concentrations. Bioconcentration factor (BCF), translocation factor (TF), and biological accumulation coefficient (BAC) were determined for each element. Our results showed that soils present low organic matter content combined with high levels of heavy metals especially Pb and Zn due to past extraction activities. Native and dominant plants sampled in these areas were classified into 14 species and eight families. Principal components analysis separated Artemisia herba-alba with high concentrations of As, Cd, Cu, Ni, and Pb in shoots from other species. Four plant species, namely, Reseda alba, Cistus libanotis, Stipa tenacissima, and Artemisia herba-alba showed strong capacity to tolerate and hyperaccumulate heavy metals, especially Pb, in their tissues. According to BCF, TF, and BAC, these plant species could be used as effective plants for Pb phytoextraction. Stipa tenacissima and Artemisia herba-alba are better suited for phytostabilization of Cd/Cu and Cu/Zn, respectively. Our study shows that several spontaneous and native plants growing on Pb/Zn contaminated sites have a good potential for developing heavy metals phytoremediation strategies.

Influence of Organic Fertilizers and Brassinosteroids on Accumulation and Uptake of as and Cd by Rice Seedlings (Oryza Sativa L.) Grown in Soil

ABSTRACT The influence of four organic fertilizers (OF) (rapeseed dregs (RD), sesame dregs (SD), bean dregs (BD), and peanut dregs (PD)), two brassinosteroids (Br) (24-epibrassinolide (Br24), and 28-homobrassinolide (Br28)), and their combination (RD+Br and BD+Br) on the accumulation and uptake of arsenic (As) and cadmium (Cd) by rice plants grown in paddy soil spiked with 40 mg kg−1 As and 5 Cd mg kg−1 was performed under waterlogged conditions. The results showed that OF, Br, and their combination significantly decreased Cd contents in shoot and root, but increased As contents in shoot of rice seedling. Iron (Fe) concentration in shoot showed a significant negative correlation with Cd concentration in shoot, but a positive correlation with As concentration in shoot. There was a positive correlation between the Fe content and As or Cd content in plaque. The application of SD, BD, and BD+Br increased the amount of iron plaque, which promoted the adsorption of As, manganese (Mn), copper (Cu), and zinc (Zn) on root surface of rice plant. These findings suggested that the application of OF, Br, and their combination in As-Cd-contaminated paddy soil was an effective approach to decrease Cd uptake by rice plant, but not for As reduction. This is a preliminary study, which has the potential for further enhancing the understanding of uptake mechanisms of As and Cd in rice plant in paddy fields.

Effect of Wheat-Solanum nigrum L. intercropping on Cd accumulation by plants and soil bacterial community under Cd contaminated soil

Using accumulators for intercropping in agricultural production can change the heavy metal concentration in the target plants. This study aims to investigate how intercropping wheat (Triticum aestivum L.) and Solanum nigrum L. affects soil bacterial community and cadmium (Cd) absorption in response to Cd-contaminated soil. We compared the concentrations and accumulations of Cd by plants, the activities of soil enzymes and the bacterial community structures of rhizosphere soil in monoculture and intercropping system. Principal component analysis (PCA) ordinations showed that soil bacterial communities were significantly separated by MW and IW, which illustrated intercropping with Solanum nigrum L. impacted the bacterial community structure of wheat. Firstly, the results showed that the biomass of shoots and roots in intercropped wheat (IW) were significantly decreased by 16.19% and 29.38% compared with monoculture wheat (MW) after 60 days after transplanting (DAT). Secondly, the Cd concentration and accumulation of shoots in IW was higher than MW. The Cd accumulation of IW shoots and roots were increased 12.87% and 0.98%, respectively after 60 days DAT. Besides, the enzymes activity [catalase (CAT), urease (UA) and alkaline phosphatase (ALP)] of IW were decreased 35%, 6% and 21%, respectively after 60 days DAT. Finally, the diversity indexes [Abundance-based Coverage Estimator (ACE), Chao and InvSimpson] of IW were lower than MW. These results indicated that intercropping with Solanum nigrum L. inhibited the wheat growth and decreased the bacterial community diversity in wheat rhizosphere, increased the Cd concentration and accumulation in plant tissues of wheat. Therefore, intercropping Solanum nigrum L. and wheat with Cd-contaminated soil might increase the risk of excessive Cd in wheat.

Effect of foliar application of selenium on morphological and physiological indices of savory (Satureja hortensis) under cadmium stress.

Cadmium is a heavy metal that pollutes the environment and affects plants physiologically and morphologically. Selenium is considered as a beneficial element, with effective roles in increasing plant tolerance to environmental stresses. A greenhouse factorial pot experiment was conducted to study the impact of selenium on traits of Savory plants under Cd stress. Experimental factors included soil contamination with cadmium (0, 75, 100, and 150 μM) and foliar spraying of selenium (0, 10, 20, and 40 μM of Sodium Selenate). Biomass, photosynthetic pigments including chlorophyll a, chlorophyll b, total chlorophyll, proline, total soluble solids, cell membrane leakage, relative water content of leaves antioxidant enzymes, and Cd and Zn concentration in shoot and root were recorded. Results revealed that Cd stress decreased vegetative growth criteria, photosynthetic pigments include chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid almost, 55%, 57%, 57%, and 68%, respectively, while poline, cell membrane leakage, peroxidase (POD), and catalase (CAT) antioxidant enzymes were increased with increasing Cd concentrations. Foliar spray of selenium reduced the toxic effects of Cd stress on savory plants via enhancing of proline content and stimulation of CAT and POD enzymes and limitation of cell membrane leakage. Also, selenium foliar spray improved chlorophyll content under Cd stress condition and decreased cadmium accumulation 29% in root, respectively. In general, these results suggest that foliar application of selenium could mitigate Cd toxicity and improve growth and antioxidant capacity of savory under different level of cadmium heavy metal stress.

Effect of soil cadmium on root organic acid secretion by forage crops.

The two forage species used in New Zealand pastoral agricultural systems, chicory (Cichorium intybus) and plantain (Plantago lanceolata) show differential ability to absorb and translocate cadmium (Cd) from roots to shoots. Chicory can accumulate Cd from even low Cd soils to levels that might exceed regulatory guidelines for Cd in fodder crops and food. Chicory and plantain were grown in soil-filled rhizocolumns under increasing Cd levels (0 (Control), 0.4, 0.8 and 1.6mg Cd/kg soil) for 60 days and showed variable secretion of oxalic, fumaric, malic and acetic acids as a function of Cd treatment. Plant roots secrete such Low Molecular Weight Organic Acids into the rhizosphere soil, which can influence Cd uptake. Chicory showed significantly (P<0.05) lower secretion of fumaric acid, and higher secretion of acetic acid than plantain at all Cd treatments. We propose that the significant secretion differences between the two species can explain the significantly (P<0.05) higher shoot Cd concentration in chicory for all Cd treatments. Understanding the mechanism for increased uptake in chicory may lead to breeding or genetic modification which yield low Cd uptake cultivars needed to mitigate the risk of Cd accumulation in pastoral agricultural food chains from this increasingly important fodder crop.