Cadmium‐induced changes in glutathione and phenolics of Thlaspi and Noccaea species differing in Cd accumulation

Glutathione (GSH) and phenolics play an important role in plant defense against metal‐ion toxicity. The antioxidant activity and metal‐binding capacity of these compounds can account for the protective effects. In contrast to animal‐cell models, however, the possible interplay among these substances in stress defense of plants is poorly investigated. This study compares the influence of cadmium (Cd) on the profiles of both soluble phenolics and GSH in shoots of different Thlaspi and Noccaea species: two ecotypes of the nonhyperaccumulator T. arvense differing in Cd resistance (ecotype Aigues Vives, Cd‐sensitive, and ecotype Jena, Cd‐resistant) and two Cd‐tolerant Cd‐Zn hyperaccumulators N. praecox and N. caerulescens (formerly Thlaspi praecox and T. caerulescens). To reveal the possible influence of Cd‐induced sulfur (S) shortage on the stress response, plants receiving normal S concentrations (500 μM MgSO₄) and plants treated with surplus S (500 μM MgSO₄ + 500 μM K₂SO₄) were analyzed. Our working hypothesis was that species differences in tolerance to high tissue Cd concentrations should be reflected by differences in endogenous levels of GSH and phenolic compounds. The results reveal clear species‐dependent differences in both the constitutive patterns and the Cd‐ and S‐induced changes in shoot concentrations of GSH and phenolics. However, no simple relationship between these shoot concentrations and Cd accumulation and tolerance can be established.     

Single and Combined Effects of Cadmium and Zinc on Carrots: Uptake and Bioaccumulation

ABSTRACT

The present study was conducted to evaluate the effects of different concentrations of cadmium (Cd) and zinc (Zn), singly and in combination, on uptake and bioaccumulation of Cd and Zn in Daucus carota L. (carrot) grown under natural field conditions. Carrot plants were treated with two Cd concentrations (10 and 100 μg mL^?1), two Zn concentrations (100 and 300 μg mL^?1), and two combined concentrations of Cd and Zn (10 + 100 and 100 + 300 μg mL^?1) 15 d after seed germination. Treatments were repeated at 10 d intervals up to 90 d of plant age. A control was also kept without a Cd or Zn treatment. Uptake, total accumulation rate (TAR), bioconcentration factor (BCF), primary transport index (PTI), secondary transport index (STI), and accumulation of Cd and Zn in root, stem, and leaf were quantified. The results show that uptake, TAR, and accumulation of Cd and Zn are concentration-dependent phenomena. Highest accumulation of Cd and Zn was found in the root, followed by the stem and then leaves. The results also showed that bioaccumulation of Cd in root, stem, and leaf was greater at the low metal-application rates of Cd and Zn in combination than at the higher rate. This study further showed that interactions of Zn and Cd are dependent on the concentrations of those metals in the soil.     

Zn accumulation and subcellular distribution in the Zn hyperaccumulator Sedurn alfredii Hance

Zn accumulation and subcellular distribution in leaves of the hyperaccumulating ecotype （HE） and non-hyperaccumulating ecotype （NHE） of Sedum alfredii Hance were studied using radiotracer and gradient centrifugation techniques. Leaf Zn accumulation in the HE of S. alfredii was 18.5-26.7 times greater than that in the NHE when the plants were grown at 1-500μmol Zn L-1. Leaf section uptake of 65Zn was highly dependent on external Zn levels. Greater 65Zn uptake in HE was noted only at external Zn levels 〉 100μmol L-1. Zinc subcellular distribution in the leaves of the two ecotypes of S. alfredii was： cell wall 〉 soluble fraction 〉 cell organelle. However, more Zn was distributed to the leaf cell wall and soluble fractions for HE than for NHE. In the leaf of HE, 91%-94% of the Zn was found in the cell walls and the soluble fraction and only 6%-9% Zn was distributed in the cell organelle fraction. For NHE, about 20%-26% Zn was recovered in the cell organelle fraction. In stems, Zn distribution to the ceil wail fraction was approximately two fold greater in the HE than that in the NHE. For the hyperaccumulating ecotype of S. alfredii, the cell wall and the vacuole played a very important role in Zn tolerance and hyperaccumulation.     

Long-Term Effects of Aluminum and Cadmium on Growth,Leaf Anatomy,and Photosynthetic Pigments of Cotton

Aluminum (Al) and cadmium (Cd) are two elements that contaminate soil in different ways as waste products of some industrial processes and that can be tolerated by some plant species in different concentrations. In this study, growth parameters of leaves and stems (fresh and dry weights, stem lengths, leaf surface area, and lamina thickness), anatomical changes in leaves (lower and upper epidermis, stomata and mesophyll tissue), and photosynthetic pigment contents (chlorophyll a and b, total chlorophyll, and carotenoids) were investigated in cotton (Gossypium hirsutum L. cv. Nazilli 84S), which was treated with Al and Cd for 3 months. Cotton seedlings were grown in greenhouse conditions and watered with Hoagland nutrient solutions, which contained 0, 100, and 200 μM aluminum chloride (AlCl₃) and cadmium chloride (CdCl₂). It was observed that reduced soil pH positively affected many parameters in cotton plants. Aluminum accumulation was greater in leaves than stems while the opposite was true for Cd accumulation. Leaves and stems of cotton plants treated with 100 and 200 μM Al and Cd showed slight growth changes; however, high concentrations of Al (200 μM) caused significant reductions in leaf area and leaf fresh weight, whereas stem fresh weight decreased with 200 μM Cd treatment. Anatomical parameters were mostly affected significantly under both concentrations of Al and Cd solutions (100 and 200 μM). The results revealed that the anatomical changes in the leaves varied in both treatments, and the long-term effect of the tested metals did not include harmful effects on anatomical structures. Moreover, the variations could be signals of tolerance or adaptive mechanisms of the leaves under the determined concentrations.     

谷氨酸N,N-二乙酸及液体肥联合强化对东南景天修复重金属污染土壤的影响

化学强化可提高超富集植物对土壤重金属的提取效果。采用盆栽试验,研究了可生物降解螯合剂谷氨酸N,N-二乙酸(GLDA)、液体肥的不同用量及复配使用对超富集植物东南景天吸收土壤重金属Cd、Zn的影响,并探讨了其渗滤液对环境的风险。结果表明:单一使用GLDA或者液体肥均能提高东南景天对土壤Cd、Zn的提取效率,其中1.25 mmol/kg GLDA处理的Cd、Zn提取量分别是空白处理的1.36,1.46倍,0.5 g/kg液体肥处理的Cd、Zn提取量分别是空白处理的1.40,1.43倍,这2种低用量单独使用的处理对Cd提取效率最高,达到41%～42%,且对应的渗滤液重金属含量均比空白处理要低,其环境风险较小。GLDA与较高用量(2 g/kg土)液体肥复配时,其东南景天对土壤Cd、Zn的提取量与空白处理相比有所下降。结果表明,GLDA和液体肥在强化植物修复方面有明显潜力,而且以低剂量单独使用强化效果较佳,值得进一步的田间试验核实。     

Cadmium and zinc accumulation in willow and poplar species grown on polluted soils

Woody plant species that produce high biomass have been proposed for use in phytoremediation technology. We investigated the accumulation of cadmium (Cd) and zinc (Zn) in Salix babylonica, S. caprea, S. dasyclados, S. matsudana × alba, S. purpurea, S. smithiana, Populus tremula, and P. nigra clones grown in a pot experiment on a Calcaric and a Eutric Cambisol (pH 7.2 and 6.4) of different levels of contamination (total metal concentrations in mg kg^–1 in soil A: 32.7 Cd, 1760 Zn; soil B: 4.34 Cd, 220 Zn). Generally, the tested clones tolerated large metal concentrations in soils and had larger Cd and Zn concentrations in leaves compared to the roots. The largest Cd concentrations in leaves were found in two clones of S. smithiana (440 mg kg^–1 on soil A; 70 mg kg^–1 on soil B). One of the S. smithiana clones had also the largest Zn concentrations (870 mg kg^–1) on soil B but accumulated slightly less Zn than a S. matsudana × alba clone (2430 mg kg^–1) on soil A. The Cd concentrations in leaves of both S. smithiana clones on soil A are the largest ever reported for soil‐grown willows. The bioconcentration factors of the best performing clone reached 15.9 for Cd and 3.93 for Zn on the less contaminated soil B. Also based on the metal contents in leaves, this clone was identified as the most promising for phytoextraction. The metal concentrations in leaves observed in the pot experiment do not reflect those found in a previous hydroponic study and the leaf‐to‐root ratios are clearly underestimated in hydroponic conditions. This demonstrates the need for testing candidates for phytoextraction crops on soils rather than in hydroponics. Our data also show that the phytoextraction potential should be tested on different soils to avoid misleading conclusions.     

外源有机酸对两种生态型东南景天吸收和积累锌的影响

通过溶液培养试验,比较研究了外源有机酸对两种生态型东南景天生长和锌吸收与积累的影响。结果表明,外加柠檬酸或草酸能明显增强非超积累生态型东南景天的耐锌毒能力,叶片、茎和根系的生物量均有增加;而对锌超积累生态型东南景天的生长没有显著性影响。外加柠檬酸、草酸或柠檬酸+草酸,锌超积累生态型根系Zn含量显著增加,但叶片和茎组织中Zn含量无明显变化;而非超积累生态型叶片、茎和根系Zn含量均显著增加,尤其是根系Zn含量,与单独Zn处理相比外源有机酸处理增加4～5倍。同样,外加柠檬酸、草酸或柠檬酸+草酸明显提高Zn在非超积累生态型根系和地上部的积累量,且对地上部Zn积累量的促进程度大于根部;柠檬酸的促进作用又比草酸及2种酸混合处理高1倍。然而,有机酸处理对Zn超积累生态型根系Zn积累量有所增加,但对叶片和茎中Zn积累量无影响。叶片和茎中水溶态Zn含量也受外源有机酸的影响,2种生态型叶片、茎中水溶态Zn含量均受有机酸处理而提高。Zn超积累生态型叶片和茎中水溶态Zn含量占总Zn含量比例也受有机酸处理而增大,但非超积累生态型则显著降低。上述结果表明,柠檬酸和草酸可能作为其Zn吸收的配基,促进根系对Zn吸收与积累,叶片和茎中的Zn可能与可溶性有机化合物或无机盐结合。     

Effect of Zinc on Cadmium Toxicity-Induced Oxidative Stress in Winter Wheat Seedlings

Two hydroponic experiments were conducted to investigate the antioxidant response of winter wheat (Triticum aestivum L.) to cadmium (Cd)-zinc (Zn) interactions, Seedlings of winter wheat (cv. Yuandong 977), were grown in modified Hoagland nutrient solution with the addition of increasing concentrations of Cd (0, 10, 25, 50 μM). In experiment 2, the seedlings of the same cultivar were treated with constant concentration of Cd (25 μM) and varying levels of Zn (0, 1, 10, 50 μM). Hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) as well as the activities of three antioxidant enzymes, catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) were monitored to estimate the amount of oxidative stress and the antioxidant ability of seedlings treated with Cd and Zn for 10 days. The results showed that levels of H₂O₂ and MDA in experiment 1 were significantly increased with increasing Cd concentrations. The data indicated that Cd could induce oxidative stress and lipid peroxidation in the plants. While H₂O₂ and MDA levels were significantly reduced by addition of Zn in experiment 2, the activities antioxidant enzymes were enhanced. A concentration of 10 μM Zn appeared to be the optimal level in this experiment for seedlings' growth, chlorophyll synthesis and antioxidant status, indicating that Zn alleviated the oxidative stress induced by Cd.     

Cadmium effects on influx and transport of mineral nutrients in plant species

Solution culture experiments were conducted under controlled environmental conditions to determine the effects of cadmium(II) [Cd(II)] activity (0, 8, 14, 28, 42, and 54 μM) on influx (IN) into roots and transport (TR) from roots to shoots of zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), calcium (Ca), magnesium (Mg), phosphorus (P), and sulfur (S) in ryegrass (Lolium perenne L.), maize (Zea mays L.), white clover (Trifolium repens L.), and cabbage (Brassica oleracea var. capitata L.). Shoot and root dry matter (DM) decreased with increased external Cd, and plant species differed extensively. Ryegrass and cabbage were relatively tolerant to Cd toxicity compared to white clover and maize. Influx and TR of Cu, Zn, Fe, Mn, Ca, and Mg were lower with increasing external Cd compared to controls, and species also differed. Influx and TR of P were enhanced in each species with up to 14 μM Cd, decreased in white clover and cabbage at higher Cd levels, while in maize and ryegrass continued to increase as Cd increased. Influx and TR of S were high in white clover at 8 μM Cd and decreased as Cd increased. Influx of S was high in ryegrass, but TR of S remained relatively constant as Cd increased. Influx and TR of S did not significantly change in maize, but decreased in cabbage as Cd increased. With Cd up to 14 μM, decreases in both IN and TR of Zn, Fe, Mn, Ca, and Mg were greater in white clover than in cabbage. Sensitivity of the dicotyledonous plant species to Cd toxicity might have been associated with Cd effects on IN and TR of Fe, Mn, Ca, and Mg. However, differences in plant sensitivities to Cd toxicity between ryegrass and maize were not reflected in Cd effects on IN and TR of mineral nutrients.     

Effects of calcium on cadmium uptake and transport in the tree species Gamblea innovans

The effect of calcium (Ca) on cadmium (Cd) accumulation in plants was investigated using Gamblea innovans Sieb. & Zucc., a deciduous tree species that is an accumulator plant for Cd and zinc (Zn). Saplings of G. innovans were grown for 3 months and fed with solutions containing only Ca (+Ca), both Ca and Cd (Ca+Cd), or only Cd (+Cd). The Ca concentration in roots was higher in both treatments containing Cd alone (+Cd) and Ca+Cd compared to roots treated with Ca alone (+Ca). In addition, the Cd concentration in roots was higher in the Ca+Cd treatment than the Cd treatment. This showed that the presence of Ca²⁺ in the rhizosphere relates with Cd uptake into roots. The result that the transport of Cd from roots through stem to leaves was suppressed by Ca treatment indicates that the presence of Ca regulates Cd transport from the roots. A clear correlation between Cd and Zn concentrations in leaves suggests a possibility that the Cd treatment accelerates the transport of Zn into leaves via the same protein transporter in this species.     

Interactive Effects of Cadmium and Zinc on Carrots: Growth and Biomass Accumulation

ABSTRACT

An experiment was carried out to assess the single and combined effects of cadmium (Cd) and zinc (Zn) on growth and component wise biomass accumulation in carrot (Daucus carota L.) plants, grown under natural field conditions. Carrot plants were raised in field and treated with 10 and 100 μ g mL^{? 1} of Cd, 100 and 300 μ g mL^{? 1} of Zn singly, and in combination through soil drench. A control was also kept without any treatments of Cd and Zn. The impacts of different treatments of Cd and Zn on carrots were evaluated in terms of number of leaves, leaf area, plant length, and component wise biomass accumulation at different plant ages. Growth indices were also calculated to assess the biomass allocation patterns in carrots. The results showed that the above parameters were significantly affected in carrots treated with Cd and Zn singly and in combination as compared to the control as well as plants treated with 100 μ g mL^{? 1} of Zn. The results also showed that treatments of Cd and Zn have significant effects on biomass allocation pattern. This study concludes that growth and biomass accumulation in carrots were significantly influenced by the concentration ratios of Cd and Zn in soil/root/stem/ leaves. It is clear from this study that combined treatments of Cd and Zn have more negative impacts on above parameters as compared to their individual treatments.     

Zinc hyperaccumulation in Thlaspi caerulescens. I. Influence on growth and mineral nutrition

Thlaspi caerulescens, a metallophyte that is able to accumulate up to 4% zinc (Zn) in leaf dry matter, has attracted much attention for its possible use in phytoremediation of metal contaminated soils. In the present study, the influence of Zn supply on mineral nutrition in T. caerulescens was investigated, in order to establish the extent to which growth stimulation by high Zn supply is related to changes in the levels of other essential nutrients. The plants were exposed to nutrient solutions containing 1.5, 100, 500, 750, 1000, or 1500 μM Zn. Zinc supply significantly influenced root and shoot concentrations of essential nutrients, but excepting Zn, the concentrations stayed within the range considered adequate for optimum growth in Brassicaceae crops. Best performance was achieved with the supply of 500 μM Zn. Growth stimulation by this treatment was accompanied by increased translocation of iron (Fe) from root to shoot and a significant correlation between shoot dry weight and Fe concentrations in shoots was found.     

Spatial heterogeneity effects of Zn/Cd-contaminated soil on the removal efficiency by the hyperaccumulator Sedum alfredii

Purpose

We aimed to examine the effects of spatial heterogeneity on Zn/Cd removal efficiency by the Zn/Cd hyperaccumulator Sedum alfredii grown on agricultural soil contaminated with mine waste.

Materials and methods

Field-collected metal-contaminated agricultural soils were arranged in pots either homogeneously or heterogeneously in “half” or “quarter” patterns. Young shoots of S. alfredii were grown on these substrates in a greenhouse.

Results and discussion

The efficiency of Zn and Cd removal from soil by S. alfredii was highest in the “quarter” pattern heterogeneous treatment, in which the percentages of total soil Zn and Cd extracted were 8.02 and 7.27, respectively. Comparing the two heterogeneous treatments, the amounts of Zn and Cd accumulated in S. alfredii shoots were significantly greater in the “quarter” pattern heterogeneous treatment than in the “half” pattern treatment.

Conclusions

We concluded that the efficiency of Zn/Cd removal increased as the scale of spatial heterogeneity decreased from “half” to “quarter”. These results may have important implications for the efficiency of phytoremediation by hyperaccumulators in the field.     

Genotypic differences in effects of cadmium on growth and nutrient compositions in wheat

Abstract

A solution culture study was conducted to determine the genotypic difference in the effects of cadmium (Cd) addition on growth and on the uptake and distribution of Cd and other 11 nutrients in wheat plants. Cadmium addition at a rate of 1 mg L^?1 significantly reduced root and shoot dry matter production, shoot height, root length, chlorophyll content, and tillers per plant. On the average of 16 wheat genotypes used in study, Cd concentrations of Cd‐treated plants were 48.1 and 459 μg g^?1 dry weight (DW) in shoots and roots, respectively, and retained 77.91% of total Cd taken up in the roots. On the whole, Cd addition reduced the concentration of sulfur (S), phosphorus (P), magnesium (Mg), molybdenum (Mo), manganese (Mn), and boron (B), and increased iron (Fe), irrespective of the plant parts. The effect of Cd on the concentration of potassium (K), calcium (Ca), and copper (Cu) differed in shoots and roots. The significant difference existed among 16 wheat genotypes in their response to Cd in terms of growth and nutrient concentrations. Genotype E81513, which showed relatively less inhibition in growth, had the lowest shoot Cd concentration and more Cd accumulation in roots, while Ailuyuang had the highest Cd concentration and accumulation in shoot with lower Cd concentration in root. The significant interaction was found between Cd treatment and genotype for all nutrient concentrations in both shoot and root, except S and Zn in root.     

Effects of sulfur supply on soybean plants exposed to zinc toxicity

Application of most waste or by‐product material increases the zinc (Zn) concentration in soils markedly. This investigation was conducted to determine if enhanced sulfur (S) supplied as sulfate (SO₄) would modify the toxic effects of excess Zn. Soybean (Glycine max [L.] Merf. cv. Rarisorri) was grown for two weeks in nutrient solutions containing ranges in Zn (0.8 to 80 μM) and S (0.02 to 20 mM). Root and shoot conditions were observed, dry weights measured, and Zri concentration determined. Zinc‐toxicity symptoms started about one week after transplanting young plants to nutrient solutions. Symptoms including chlorosis, especially in the trifoliate leaves, and change in orientation of unifoliate leaves were mild in 20 μM‐, intermediate in 40 μM‐, and severe in 80 μM Zn‐containing solutions. Dry weight was reduced in plants exposed to 20, 40, and 80 μM Zn. Plants grown in 40 μM Zn and 20 mM S survived longer than those grown in lower S concentrations and showed alleviation of the chlorosis in trifoliate leaves. The change in the orientation of the unifoliate leaves due to Zn toxicity, however, was not affected by S. Zinc contents in shoots grown at toxic Zn levels were higher in 20 mM‐ than in lower S‐containing nutrient solutions. High S supply (20 mM) increased Zn translocation from roots to shoots. Besides increasing the Zn translocation from roots to shoots, it seems that S nutrition may also be a factor helping the plants to cope with high levels of Zn in their tissues.     

Effects of Nickel on Growth and Composition of Metal Micronutrients in Barley Plants Grown in Nutrient Solution

Abstract

A hydroponic experiment was conducted in a phytotron at pH 5.5 to study the effects of nickel (Ni) on the growth and composition of metal micronutrients, such as copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn), of barley (Hordeum vulgare L. cv. Minorimugi). Four Ni treatments were conducted (0, 1.0, 10, and 100 μM) for 14 d. Plants grown in 100 μM Ni showed typical visual symptoms of Ni toxicity such as chlorosis, necrosis of leaves, and browning of the root system, while other plants were free from any symptoms. Dry weights were the highest in plants grown in 1.0 μM Ni, with a corresponding increase in the chlorophyll index of the plants, suggesting that 1.0～10 μM Ni needs to be added to the nutrient solution for optimum growth of barley plants. The increase of Ni in the nutrient solutions increased the concentrations of Cu and Fe in roots, while a decrease was observed in shoots. The concentrations of Mn and Zn in shoots and roots of plants decreased with increasing Ni supply in the nutrient solution. Shoot concentrations of Cu, Fe, Mn, and Zn in plants grown at 100 μ M Ni were below the critical levels for deficiency. Plants grown at 1.0 μ M Ni accumulated higher amounts of Cu, Fe, Mn and Zn, indicating that nutrient accumulation in plants was more influenced by dry weights than by nutrient concentrations. The translocation of Cu and Fe from roots to shoots was repressed, while that of Mn and Zn was not repressed with increasing Ni concentration in the nutrient solution.     

Cadmium Stress in Barley: Growth,Leaf Pigment,and Protein Composition and Detoxification of Reactive Oxygen Species

Barley seedlings (Hordeum vulgare L., cv. ‘Obzor’) were exposed for 5 d to 0, 5, 50, and 500 μM CdCl₂ in nutrient solution. Cadmium (Cd) treatment caused a reduction of plant length, biomass, and leaf pigment content. The level of soluble leaf proteins was not changed significantly. SDS-PAGE revealed a slight diminution of Rubisco subunits and the appearance of a new low molecular mass band after exposure to 50 or 500 μM Cd. The antioxidative protection in leaves under Cd toxicity was studied in its complexity. Slightly diminished superoxide dismutase, enhanced catalase, and drastically increased total peroxidase activities were found at the highest Cd level. Ascorbate peroxidase activity was not changed significantly. The isoenzyme patterns of the antioxidant enzymes under study were only slightly altered without synthesis of new isoforms. The content of oxidized ascorbate increased during exposure to 50 and 500 μM Cd. The level of H₂O₂ rose only at 500 μM Cd without accumulation of malondialdehyde and oxidized proteins. Non-protein thiol groups increased up to four-fold after exposure to 50 and 500 μM Cd. The results are in accordance with the induction of mechanisms allowing an immobilization and sequestration of Cd in barley leaves, and suggest only minor effects via oxidative damage.     

Cadmium‐induced alterations in nutrient composition and growth of betula pendula seedlings: The significance of fine roots as a primary target for cadmium toxicity

Birch seedlings (Betula pendula) were cultivated in nutrient solution with 0–2 μM cadmium (Cd). The effects of 2–10 days of Cd exposure on root and shoot element composition [potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), sulfur (S), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), and Cd] and growth (as percentage dry weight increase) were investigated. The element composition of fine roots and remaining root parts were analysed separately to elucidate the significance of the fine roots as a primary target for Cd toxicity. The nutrient composition of the roots was considerably altered by the Cd exposures, whereas the nutrient composition of the shoot was less affected. After eight days, the whole root (fine roots + remaining roots) concentrations of K, Ca, Mg, and Mn were reduced, whereas the opposite was found for Cu and Mo. The element distribution between fine roots and remaining roots was altered by the Cd exposures. Cadmium was accumulated in the roots and in fine roots especially. Fine roots also exhibited a capacity for Cu accumulation and a retainment of Ca and S. Total plant growth was stimulated by 0.05 μM Cd but was reduced by the 0.5–2 μM Cd treatments. Root growth was increased by the Cd exposures and growth reductions were restricted only to the shoot. Accumulation of Cd and Cu and a retainment of Ca and S in the fine roots together with a preference for root growth, imply that the explanation for the Cd effects obtained may include mechanisms for Cd tolerance.     

Metal removal from and microbial property improvement of a multiple heavy metals contaminated soil by phytoextraction with a cadmium hyperaccumulator Sedum alfredii H.

Purpose

Effects of phytoextraction by Sedum alfredii H., a native cadmium hyperaccumulator, on metal removal from and microbial property improvement of a multiple heavy metals contaminated soil were studied under greenhouse conditions.

Materials and methods

A rhizobox experiment with an ancient silver-mining ecotype of S. alfredii natively growing in Zhejiang Province, China, was conducted for remediation of a multiple heavy metals contaminated soil. The rhizobox was designed combining the root-shaking method for the separation of rhizospheric vs near-rhizospheric soils and prestratifying method for separation of sublayers rhizospheric soils (0–10 mm from the root) and bulk soil (>10 mm from the root). Soil and plant samplings were carried out after 3 and 6 months of plant growth.

Results and discussion

Cadmium (Cd), zinc (Zn), and lead (Pb) concentrations in shoots were 440.6, 11,893, and 91.2 mg kg^?1 after 6 months growth, and Cd, Zn, and Pb removed in the shoots were 0.862, 25.20, and 0.117 mg/plant. Microbial biomass C, basal respiration, urease, acid phosphatase, and invertase activities of the rhizospheric soils were significantly higher than that of unplanted soils after 6 months growth. Microbial biomass carbon (MBC) of 0–2 mm and basal respiration (BR) rate of 0–8 mm sublayer rhizospheric soils were significantly higher than that of bulk soil after 6 months growth. So were the three enzyme activities of 0–4 mm sublayer rhizospheric soils. BR rate and urease were significantly negatively correlated with soluble Cd, so were MBC, acid phosphatase, and intervase activities with soluble Zn, MBC, BR rate, and three enzyme activities with soluble Pb.

Conclusions

Harvesting shoots of S. alfredii could remove remarkable amounts of Cd, Zn, Pb, and lower water-soluble Cd, Zn, and Pb concentrations in the rhizospheric soils. MBC, BR rate, and enzyme activities of the metal polluted soil, especially the rhizospheric soils increased with phytoextraction process, which is attributed to the stimulation of soil microbes by planting as well as the decrease in soil-soluble metal concentration.     

Phytoextraction of Heavy Metals by Eight Plant Species in the Field

Phytoremediation is an in situ, cost-effective potential strategy for cleanup of sites contaminated with trace metals. Selection of plant materials is an important factor for successful field phytoremediation. A field experiment was carried out to evaluate the phytoextraction abilities of six high biomass plants (Vertiveria zizanioides, Dianthus chinensis, Rumex K-1 (Rumex upatientia × R. timschmicus), Rumex crispus, and two populations of Rumex acetosa) in comparison to metal hyperaccumulators (Viola baoshanensis, Sedum alfredii). The paddy fields used in the experiment were contaminated with Pb, Zn, and Cd. Our results indicated that V. baoshanensis accumulated 28 mg kg^?1 Cd and S. alfredii accumulated 6,279 mg kg^?1 Zn (dry weight) in shoots, with bioconcentration factors up to 4.8 and 6.3, respectively. The resulting total extractions of V. baoshanensis and S. alfredii were 0.17 kg ha^?1 for Cd and 32.7 kg ha^?1 for Zn, respectively, with one harvest without any treatment. The phytoextraction rates of V. baoshanensis and S. alfredii for Cd and Zn were 0.88 and 1.15%, respectively. Among the high biomass plants, R. crispus extracted Zn and Cd of 26.8 and 0.16 kg ha^?1, respectively, with one harvest without any treatment, so it could be a candidate species for phytoextraction of Cd and Zn from soil. No plants were proved to have the ability to phytoextract Pb with high efficiency.