Cd Supply Research Articles

Assessment of the capability of cadmium accumulation and translocation among 31 willows: four patterns of willow biomass variation response to cadmium.

Cadmium (Cd) pollution threatens food security and the environment. Willow species (Salix, Salicaceae) exhibit a remarkable potential to restore Cd-polluted sites due to their high biomass production and high Cd accumulation capacities. This study examined the Cd accumulation and tolerance in 31 genotypes of shrub willow in hydroponic conditions at varying Cd levels (0μM Cd, 5μM Cd, and 20μM Cd). The root, stem, and leaf biomass of 31 shrub willow genotypes showed significant differences to Cd exposure. Among 31 willow genotypes, four patterns of biomass variation response to Cd were identified: insensitive to Cd; growth inhibition due to excessive Cd supply (high Cd inhibition); low Cd causing inhibited growth, whereas high Cd leading to increased biomass (U-shape); and growth increment with excessive Cd exposure (high Cd induction). The genotypes belonging to the "insensitive to Cd" and/or "high Cd induction" were candidates for the utilization of phytoremediation. Based on the analysis of Cd accumulation of 31 shrub willow genotypes at high and low Cd levels, genotypes 2372, 51-3, and 1052 obtained from a cross between S. albertii and S. argyracea grew well and accumulated relatively more Cd levels than other genotypes. In addition, for Cd-treated seedlings, root Cd accumulation was positively correlated with shoot Cd accumulation and total Cd uptake, demonstrating that Cd accumulation in roots could serve as a biomarker for evaluating the Cd extraction capacity of willows, especially in hydroponics screening. The results of this study screened out willow genotypes with high Cd uptake and translocation capacities, which will provide valuable approaches for restoring Cd-contaminated soils with willows.

Cadmium isotope fractionation and gene expression evidence for tracking sources of Cd in grains during grain filling in a soil-rice system

Grain filling is the key period that causes excess cadmium (Cd) accumulation in rice grains. Nevertheless, uncertainties remain in distinguishing the multiple sources of Cd enrichment in grains. To better understand the transport and redistribution of Cd to grains upon drainage and flooding during grain filling, Cd isotope ratios and Cd-related gene expression were investigated in pot experiments. The results showed that the Cd isotopes in rice plants were much lighter than those in soil solutions (∆114/110Cdrice-soil solution = −0.36 to −0.63 ‰) but moderately heavier than those in Fe plaques (∆114/110Cdrice-Fe plaque = 0.13 to 0.24 ‰). Calculations revealed that Fe plaque might serve as the source of Cd in rice (69.2 % to 82.6 %), particularly upon flooding at the grain filling stage (82.6 %). Drainage at the grain filling stage yielded a larger extent of negative fractionation from node I to the flag leaves (∆114/110Cdflag leaves-node I = -0.82 ± 0.03 ‰), rachises (∆114/110Cdrachises-node I = -0.41 ± 0.04 ‰) and husks (∆114/110Cdrachises-node I = -0.30 ± 0.02 ‰), and significantly upregulated the OsLCT1 (phloem loading) and CAL1 (Cd-binding and xylem loading) genes in node I relative to that upon flooding. These results suggest that phloem loading of Cd into grains and transport of Cd-CAL1 complexes to flag leaves, rachises and husks were simultaneously facilitated. Upon flooding of grain filling, the positive fractionation from the leaves, rachises and husks to the grains (∆114/110Cdflag leaves/rachises/husks-node I = 0.21 to 0.29 ‰) is less pronounced than those upon drainage (∆114/110Cdflag leaves/rachises/husks-node I = 0.27 to 0.80 ‰). The CAL1 gene in flag leaves is down-regulated relative to that upon drainage. Thus, the supply of Cd from the leaves, rachises and husks to the grains is facilitated during flooding. These findings demonstrate that the excess Cd was purposefully transported to grain via xylem-to-phloem within nodes I upon the drainage during grain filling, and the expression of genes responsible for encoding ligands and transporters together with isotope fractionation could be used to tracking the source of Cd transported to rice grain.

Cadmium and zinc accumulation behaviour of hyperaccumulator Arabidopsis halleri ssp. gemmifera in the hydroponic system

<p><em>Arabidopsis halleri </em>ssp. <em>gemmifera</em> is classified as Cd and Zn hyperaccumulator plant, however, the disparity accumulation preferences in organs (root, stem and leaves) between cadmium and zinc seems less understandable. Therefore, this study aimed to portray accumulation behaviour toward the presence of Cd and Zn in the hydroponic method employing <em>A. halleri </em>ssp.<em> gemmifera</em>. The experiment was conducted by applying this plant using 2 and 300 µM of Cd, and 2 and 200 µM Zn, together with 20% Hoagland solution for 7 days, separately. The results showed that Zn in the medium was uptake faster than Cd. Furthermore, increasing Cd/Zn supply at the medium resulted in an increasing accumulation of Cd/Zn in the organs of the plant. In both Cd treatments, the accumulation followed the order of stem>root>leaves, indicating Cd transportation to the upper part has occurred during this period. The same accumulation preference pattern was also reported in the 200 µM Zn supply. However, at 2 µM Zn supply, Zn accumulation was mainly found in the leaves, followed by the root and stem. <em>A. halleri </em>ssp. <em>gemmifera</em> uptake Zn faster from the medium and translocate rapidly to the leaves at low-level Zn supply. Increasing Zn supply concentration might inhibit the translocation of Zn from stem to leaves. Meanwhile, regardless of Cd supply concentrations, this plant could only translocate Cd to the stem mostly within a short-time exposure period. Therefore, this study concluded that <em>A. halleri </em>ssp. <em>gemmifera </em>exhibited different accumulation responses when exposed to different Cd and Zn supply concentrations.</p>

Subcellular localization and chemical speciation of Cd in Arabidopsis halleri ssp. gemmifera to reveal its hyperaccumulating and detoxification strategies

The study involving low-level Cd using Arabidopsis halleri ssp. gemmifera is likely suitable for realistic Cd phytoremediation since the available Cd in the contaminated soil is considered low. However, the comprehensive evidence on how this plant undergoes hyperaccumulating-detoxification strategies under low Cd levels in its root, stem, and leaves remained questionable. Therefore, Cd uptake and distribution, intracellular localization, Cd speciation, and metal chelation compounds, glutathione (GSH) and phytochelatins (PCs), were assessed in a time-course analysis to portray their involvement in the Cd hyperaccumulating mechanisms. The results showed that under low Cd stress, 0.3 µmol/L of Cd was completely absorbed by this plant during 336 h, indicating a high Cd uptake system. At the same time, more Cd content accumulated in the stem and leaves compared to Cd content in the root. Excessive Cd being transported to the upper part was supported by the availability of more than 80% of Cd speciation categorized as mobile fractions (ethanol-and H 2 O-extractable forms). The highest Cd soluble fraction found in the root during initial and middle exposure promoted Cd intracellular translocation to stem and leaves. At the end of exposure (336 h), we predicted Cd was compartmentalized in the less metabolite sites, cell wall and vacuole due to less toxicity effect, which was also found in high Cd level (30 µmol/L). Furthermore, GSH and PC as metal complexation compounds owned a minor role even under high Cd exposure level. Therefore, regardless of the Cd supply level, elevating of metal transport and sequestration in the shoots were preferred over thiol complexed forms as common hyperaccumulating strategies in A. halleri ssp. gemmifera. • At low Cd supply, Arabidopsis halleri ssp. gemmifera does not accumulate in the root. • Cd is finally sequestrated in the leaves and existed mainly as soluble fraction. • More than 80 % of Cd chemical form in the tissues was mobile forms. • Glutathione and phytochelatins play a minor role in Cd chelating mechanisms.

The Content of Cd and Pb in Herbs and Single-Component Spices Used in Polish Cuisine

Spices and herbs play an important role in the human diet, mostly due to the presence of essential oils and high antioxidant activity. Therefore, the toxicity of metals raises concerns about the safety of consumption of spices and herbs. This paper examines the content of Cd and Pb in fresh and dried herbs and single-component spices that are the most popular in Polish cuisine: 100 samples of nine kinds of dried herbs, 184 samples of 15 kinds of fresh herbs and 148 samples of 14 kinds of loose single-component spices. The level of Cd and Pb was determined using the GF AAS method. The safety of herbs and spices for consumption was estimated based on the percentage intake of Cd and Pb compared with the tolerable intake (% TWI, % BMDL), chronic daily intake (CDI), target hazard quotient (THQ), hazard index (HI) and comparisons of the results of chemical analyses with the maximum admissible levels of Cd and Pb in Poland and in the European Union. Calculated per fresh weight of the product, dried herbs on average contained 0.134 ± 0.168 mg of Cd and 0.548 ± 0.161 mg of Pb per kg−1, fresh herbs on average contained 0.004 ± 0.007 mg of Cd and 0.039 ± 0.033 mg of Pb per kg−1, and the mean content of Cd in spices was 0.017 ± 0.019 mg per kg−1 and 0.064 ± 0.050 mg of Pb. The % TWI, % BMDL, CDI, THQ and HI (Cd + Pb) for all the analysed products were lower than 1. The results do not imply a risk due to the supply of Cd and Pb with the diet to the human body, primarily due to the small intake of these products. However, it should be highlighted that the content of Cd in dried coriander and estragon and that of Pb in watercress, jiaogulan, celery, basil and dill exceeded the acceptable limit. Thus, their consumption for people from particularly sensitive groups such as babies, pregnant and breastfeeding women and people should be carefully limited.

Electric Field-Enhanced Cadmium Accumulation and Photosynthesis in a Woody Ornamental Hyperaccumulator-Lonicera japonica Thunb.

The multi-system of electro-phytotechnology using a woody ornamental cadmium (Cd) hyperaccumulator (Lonicera japonica Thunb.) is a new departure for environmental remediation. The effects of four electric field conditions on Cd accumulation, growth, and photosynthesis of L. japonica under four Cd treatments were investigated. Under 25 and 50 mg L−1 Cd treatments, Cd accumulation in L. japonica was enhanced significantly compared to the control and reached 1110.79 mg kg−1 in root and 428.67 mg kg−1 in shoots influenced by the electric field, especially at 2 V cm−1, and with higher bioaccumulation coefficient (BC), translocation factor (TF), removal efficiency (RE), and the maximum Cd uptake, indicating that 2 V cm−1 voltage may be the most suitable electric field for consolidating Cd-hyperaccumulator ability. It is accompanied by increased root and shoots biomass and photosynthetic parameters through the electric field effect. These results show that a suitable electric field may improve the growth, hyperaccumulation, and photosynthetic ability of L. japonica. Meanwhile, low Cd supply (5 mg L−1) and medium voltage (2 V cm−1) improved plant growth and photosynthetic capacity, conducive to the practical application to a plant facing low concentration Cd contamination in the real environment.

Cadmium transfer between maize and soybean plants via common mycorrhizal networks

More than 80% terrestrial plants establish mutualistic symbiosis with soil-borne arbuscular mycorrhizal fungi (AMF). These fungi not only significantly improve plant nutrient acquisition and stress resistance, but also mitigate heavy metal phytotoxicity, Furthermore, the extraradical mycorrhizal mycelia can form common mycorrhizal networks (CMNs) that link roots of multiple plants in a community. Here we show that the networks mediate migration of heavy metal cadmium (Cd) from maize (Zea mays L.) to soybean (Glycine max (Linn.) Merr.) plants. CMNs between maize and soybean plants were established after inoculation of maize plants with AMF Funneliformis mosseae. Application of CdCl2 in maize plants led to 64.4% increase in the shoots and 48.2% increase in the roots in Cd content in CMNs-connected soybean plants compared to the control without Cd treatment in maize. Meanwhile, although the CMNs-connected soybean plants did not directly receive Cd supply, they upregulated transcriptional levels of Cd transport-related genes HATPase and RSTK 2.13- and 5.96-fold, respectively, induced activities of POD by 44.8% in the leaves, and increased MDA by 146.2% in the roots. Furthermore, Cd addition inhibited maize growth but mycorrhizal colonization improved plant performance in presence of Cd stress. This finding demonstrates that mycorrhizal networks mediate the transfer of Cd between plants of different species, suggesting a potential to use CMNs as a conduit to transfer toxic heavy metals from main food crops to heavy metal hyperaccumulators via intercropping.

Comparing soil-to-plant cadmium (Cd) transfer and potential human intake among rice cultivars with different Cd tolerance levels grown in a tropical contaminated soil.

With its accumulation in upland rice, cadmium (Cd) can easily enter the human food chain, which poses a global health threat considering nearly half of the human population depends on rice as a staple food source. A study was conducted to (1) evaluate Cd accumulation by rice cultivars, grown in Cd-polluted Tropical Oxisols, with different levels of Cd tolerance; (2) quantify Cd transfer from soil to rice shoots and grain; and (3) estimate daily Cd intake by humans. Three rice cultivars, characterized by low (Cateto Seda-CS), medium (BRSMG Talento-BT), and high (BRSMG Caravera-BC) Cd uptake capacity, were investigated. Rice cultivars were exposed to increasing soil Cd concentrations (0.0, 0.7, 1.3, 3.9, 7.8, and 11.7mgkg-1). Analysis was performed on soil, shoots, and grain. Shoot biomass and grain yield decreased with increasing Cd supply, suggesting the following Cd tolerance: CS > BT > BC. Cadmium concentrations in shoots and grain increased when exposed to Cd. Only CS did not exceed the maximum Cd limit permitted in food (0.40mgkg-1), when rates up to 1.3mgkg-1 of Cd were applied to soil. Considering daily rice consumption levels in Brazil, Cd intake often exceeds maximum tolerable levels. Continuous monitoring of soil Cd concentrations is a pivotal step in avoiding hazards to humans. Such monitoring is important on a global scale since outside of Asia, Brazil is the leading rice-producing and rice-consuming country.

Predicting soil cadmium uptake by plants in a tailings reservoir during 48-year vegetation restoration

Plant uptake can reduce soil cadmium (Cd) pollution, while how to exactly predict plant Cd uptake in industrial or mining areas during vegetation restoration remains unexplored. Taking Heteropogon contortus as the object plant, we predicted plant Cd uptake in the Majiatian tailings reservoir during 48-year vegetation restoration by the methods of soil total Cd, DGT (diffusive gradients in thin films technique) and acetic acid (HAc) extraction. Meanwhile, we explored the effects of soil properties on the accuracy of the prediction. Total Cd concentrations in the soils exhibited a better prediction of plant Cd uptake relative to the methods of HAc extraction and DGT. However, the DGT method effectively predicted plant Cd uptake at low Cd supply (lower than 0.42 μg/L), probably because of the dominant diffusion limitation by plants. The prediction of plant Cd uptake by HAc extraction was improved when combined with soil pH. Our results indicate that with increasing external Cd inputs during the vegetation restoration, soil total Cd and traditional extraction method in combination with soil properties are effective ways to predict plant Cd uptake, especially when the Cd fractions cannot be measured by DGT. However, the DGT method works once plant Cd uptake dominated by diffusion limitation despite the interference in soil properties.

A time-series of heavy metal geochemistry in sediments of Galveston Bay estuary, Texas, 2017-2019

Galveston Bay is an anthropogenic-influenced estuary where industrial runoff, wastewater, and shipping vessel discharges enter the bay alongside natural freshwaters. Here, heavy metal concentrations in Galveston Bay surface sediment (2-year quarterly time-series) and a single sediment core are presented to explore the anthropogenic and geochemical controls on the spatiotemporal distributions, fluxes, sources, and potential toxicity of metals within this estuary. Samples were leached to distinguish authigenic sediment coatings from geogenic crystalline material. Spatial differences dominate the observed concentration variability, with higher metal concentrations in eastern vs. western bay sediments, as the eastern bay is where metals are flocculated from the dissolved phase and/or sediments are hydrodynamically trapped. Temporal variations are a secondary controlling factor, with sediment metal concentrations positively correlated with Trinity River discharge. Core data indicate stable Fe, Pb Ni, Cd and Hg levels during the 20th century but increasing Cu and Zn levels in recent years. Galveston Bay sediments are potentially toxic for As, Cd, Cr, Cu, Ni, Sb, Zn and Hg, based on federal toxicity standards. Enrichment factors and statistical analyses suggest that Ni and Cr originate from natural sources, while anthropogenic sources dominate supply of As, Cd, Hg, Ni, Pb, Sb, and Zn. This unique time-series shows that major flooding events, such as Hurricane Harvey in 2017, affect surface sediment metal distributions in Galveston Bay, but not any more than the natural geochemical controls on spatiotemporal distributions of metals in anthropogenic-influenced estuaries.

Hydrocotyle vulgaris L.: a new cadmium-tolerant landscape species and its physiological responses to cadmium exposure.

Landscape plants have both ecological and aesthetic value and may also represent ideal candidates for phytoremediation. In the present study, one round of hydroponic culture for 14 days with different cadmium (Cd) concentrations (0, 0.5, 1, and 2 mg L-1 Cd) was carried out to test whether Hydrocotyle vulgaris L. is a Cd-tolerant plant. Furthermore, physiological parameters, including pigment concentrations, photosynthesis, antioxidant enzyme activities (AEAs), and nutrient uptake, were also examined to determine the tolerance of H. vulgaris to Cd exposure. The results showed that H. vulgaris could grow normally under all Cd supply levels. The Cd removal efficiency reached 100% at Cd concentrations ≤1.0 mg L-1. The concentrations of Cd in roots and shoots increased (P < 0.05) with Cd supplementation. The maximum concentrations of Cd reached 26.4 and 118 mg kg-1 in shoots and roots, respectively. The translocation factor values were similar under all Cd treatments. The highest mean daily increase in biomass (MDIB) was obtained under 1 mg L-1 Cd exposure, which increased by 69.86% compared to that in the control, which may be due to the increased photosynthetic pigments, photosynthetic rate, and the consistent nutrient concentrations under this Cd level, as there were positive relationships between these parameters and MDIB. Moreover, the activities of AEA also generally explicated highest among all Cd levels. All these results indicate that the above physiological parameters play a positive role in promoting plant growth and alleviating Cd stress. In summary, H. vulgaris was verified as a potential Cd-tolerant plant, providing new information for Cd phytoremediation. Furthermore, given its extensive habitat distribution, this species might be tested for phytoremediation of contaminated soils in future work.

Cadmium toxicity in Salvia sclarea L.: An integrative response of element uptake, oxidative stress markers, leaf structure and photosynthesis

The herbal plant Salvia sclarea L. (clary sage) is classified to cadmium (Cd) accumulators and considered as a potential plant for phytoremediation of heavy metal polluted soil. However, the effect of Cd only treatment on the function of the photosynthetic apparatus of S. sclarea, as well as the mechanisms involved in Cd tolerance have not yet been studied in detail. This study was conducted to examine the integrative responses of S. sclarea plants exposed to a high Cd supply (100 µM) for 3 and 8 days by investigating element nutrient uptake, oxidative stress markers, pigment composition, photosynthetic performance and leaf structure. Measurements of the functional activities of photosystem I (PSI, by P700 photooxidation), photosystem II (PSII, by chlorophyll fluorescence parameters), the oxygen-evolving complex (oxygen evolution by Joliot- and Clark-type electrodes), as well as the leaf pigment and phenolic contents, were used to evaluate the protective mechanisms of the photosynthetic apparatus under Cd stress. Data suggested that the molecular mechanisms included in the photosynthetic tolerance to Cd toxicity involve strongly increased phenolic and anthocyanin contents, as well as an increased non-photochemical quenching and accelerated cyclic electron transport around PSI up to 61%, which protect the function of the photosynthetic apparatus under stress. Furthermore, the tolerance of S. sclarea to Cd stress is also associated with increased accumulation of Fe in leaves by 25%. All the above, clearly suggest that S. sclarea plants employ several different mechanisms to protect the function of the photosynthetic apparatus against Cd stress, which are discussed here.

Coordination between root cell wall thickening and pectin modification is involved in cadmium accumulation in Sedum alfredii.

Root cell wall (RCW) modification is a widespread important defense strategy of plant to cope with trace metals. However, mechanisms underlying its remolding in cadmium (Cd) accumulation are still lacking in hyperaccumulators. In this study, changes of RCW structures and components between nonhyperaccumulating ecotype (NHE) and hyperaccumulating ecotype (HE) of Sedum alfredii were investigated simultaneously. Under 25μM Cd treatment, RCW thickness of NHE is nearly 2 folds than that of HE and the thickened cell wall of NHE was enriched in low-methylated pectin, leading to more Cd trapped in roots tightly. In the opposite, large amounts of high-methylated pectin were assembled around RCW of HE with Cd supply, in this way, HE S.alfredii decreased its root fixation of Cd and enhanced Cd migration into xylem. TEM and AFM results further confirmed that thickened cell wall was caused by the increased amounts of cellulose and lignin while root tip lignification was resulted from variations of sinapyl (S) and guaiacyl (G) monomers. Overall, thickened cell wall and methylated pectin have synchronicity in spatial location of roots, and their coordination contributed to Cd accumulation in S.alfredii.

Chemical Speciation and Distribution of Cadmium in Rice Grain and Implications for Bioavailability to Humans.

Consumption of rice (Oryza sativa) is the major dietary source of cadmium (Cd) for populations with rice as the staple. Little is known about the distribution and chemical speciation of Cd in rice grain, which is critical in determining the bioavailability of Cd to humans. We used synchrotron-based techniques for analyses of the speciation and distribution of Cd in rice grain. The majority of the Cd in rice grain was present as Cd-thiolate complexes (66-92%), likely in the form of Cd bound with thiol-rich proteins. The remainder was present as Cd-carboxyl compounds and Cd-histidine. Elemental mapping showed two different patterns of Cd distribution, one with an even distribution throughout the entire grain and the other with a preferential distribution in the outer tissues (aleurone layer and outer starchy endosperm). The distribution pattern is important as it affects the removal of Cd during milling. On average, milling reduced grain Cd concentrations by 23.5% (median of 27.5%), although the range varied widely from a 64.7% decrease to a 22.2% increase, depending upon the concentration of Cd in the bran. We found that the variation in the distribution pattern of Cd in the rice grain was due to a temporal change in the supply of Cd from the soil porewater during grain filling. These results have important implications for Cd bioavailability in human diets.

Distribution and metal contamination in core sediments from the North Al-Wajh area, Red Sea, Saudi Arabia

Forty-one bottom sediment samples were collected from three cores at the mouth of Wadi Haramel, Wadi Antar, Wadi Dumaygh, north of Al-Wajh, Red Sea, Saudi Arabia, to evaluate the levels of heavy metal contamination, using the enrichment factor (EF), geoaccumulation index (Igeo), contamination factor (Cf), soil pollution index (SPI), and multivariate statistical analysis (hierarchical cluster analysis and principal component analysis). Fe, Al, Pb, Mn, Cu, Ni, Co, Cd, Sr, V, Hg, and Total Organic Matter (TOM%) were quantified by Atomic Absorption Spectrophotometer. The vertical distribution of the heavy metals concentrations increased upwards indicating high heavy metals input. The results of enrichment factor and soil pollution index calculations indicate a strong anthropogenic supply of Cd and Sr (SPI = 1.10, 2.70, EF = 18.25, 17.99 respectively) while Cu and Ni show moderate anthropogenic input from urban, industrial activities and some new projects in the northern coast of Saudi Arabia.

Selenium Modulates the Level of Auxin to Alleviate the Toxicity of Cadmium in Tobacco

Cadmium (Cd) is an environmental pollutant that potentially threatens human health worldwide. Developing approaches for efficiently treating environmental Cd is a priority. Selenium (Se) plays important role in the protection of plants against various abiotic stresses, including heavy metals. Previous research has shown that Se can alleviate Cd toxicity, but the molecular mechanism is still not clear. In this study, we explore the function of auxin and phosphate (P) in tobacco (Nicotiana tabacum), with particular focus on their interaction with Se and Cd. Under Cd stress conditions, low Se (10 μM) significantly increased the biomass and antioxidant capacity of tobacco plants and reduced uptake of Cd. We also measured the auxin concentration and expression of auxin-relative genes in tobacco and found that plants treated with low Se (10 μM) had higher auxin concentrations at different Cd supply levels (0 μM, 20 μM, 50 μM) compared with no Se treatment, probably due to increased expression of auxin synthesis genes and auxin efflux carriers. Overexpression of a high affinity phosphate transporter NtPT2 enhanced the tolerance of tobacco to Cd stress, possibly by increasing the total P and Se content and decreasing Cd accumulation compared to that in the wild type (WT). Our results show that there is an interactive mechanism among P, Se, Cd, and auxin that affects plant growth and may provide a new approach for relieving Cd toxicity in plants.

Investigation of the effects of salt (NaCl) stress and cadmium (cd) toxicity on growth and mineral acquisition of Vuralia turcica

The effects of increasing concentrations of salt (NaCl) and cadmium (Cd) on shoot weight and shoot mineral content was investigated in Vuralia turcica, which is endemic to Turkey. In the present study, tolerance mechanisms to salt and Cd stress of V. turcica were examined. Plants were grown in calcareous soil, which has low organic content (1.03%) and high pH (8.4), and treated with increasing NaCl (0, 1000, and 2000 ppm) and Cd (0, 5, 25, and 50 ppm) with four replicates for a month under greenhouse conditions. The shoots of each plant were harvested and analyzed for mineral element content as well as the activities of antioxidative enzymes. Cd and Na concentrations of V. turcica were increased by enhanced NaCl and Cd supply. Increasing NaCl supply reduced the dry weight of shoots of V. turcica. Supplying a low concentration (5 ppm) of Cd increased dry weight, whereas 25 and 50 ppm Cd decreased dry weight. No visual symptoms were observed on leaves exposed to both salt and Cd stress. The activities of antioxidative defense enzymes were similar in both stress conditions when compared to non-stressed control groups.

Phase stability and strain accumulation in CdO as a function of Cd/O supply during MOVPE synthesis

A prominent trend for the stabilization of zincblende or wurtzite phases in CdO is observed. Typically, CdO occurs in its “equilibrium” rocksalt phase when grown on r-plane oriented sapphire substrates employing Cd-rich growth conditions. Gradual decrease of Cd supply, i.e. moving towards O-rich condition, results in additional phases, firstly zincblende and secondly wurtzite. Importantly, the variation of Cd/O ratios at the reaction zone was tuned by changing both the precursor flow rates and the growth temperature affecting the precursor decomposition. Moreover, an interesting strain accumulation trend, correlating with the band gap variations was observed as a function of Cd/O supply ratios too. In particular, a gradual change towards O-rich conditions leads to a build-up of strain in the films and red-shifts the optical absorption edge.

Cadmium phytoextraction potential of king grass (Pennisetum sinese Roxb.) and responses of rhizosphere bacterial communities to a cadmium pollution gradient.

Screening for tolerant and high biomass producing plants is important for phytoextraction efforts in remediating agricultural soils contaminated by heavy metals. We carried out a greenhouse experiment involving a soil cadmium (Cd) concentration gradient (0.1, 0.5, 1, 2, 4, and 8mgkg-1) to assess growth and phytoextraction capacity of king grass (Pennisetum sinese Roxb.) in soils contaminated by Cd and to explore changes in diversity and structure of rhizosphere soil bacterial communities in response to long-term Cd pollution. A significant positive relationship was observed between Cd concentrations in P. sinese stems, leaves, and roots and soil Cd concentration. The highest Cd concentrations in shoots and roots were 28.87 and 34.01mgkg-1, respectively, at 8mgkg-1of soil Cd supply. Total extraction amounts of Cd in P. sinese were 0.22-1.86mgplant-1 corresponding to treatment with 0.5-8mgkg-1 Cd. Most of the Cd was stored in shoots, and the largest accumulation was 1.56mgplant-1 with 54.02g dry shoot weight. After phytoextraction, changes in rhizobacterial community composition were found with different levels of Cd application, whereas there were no clear trends in diversity and richness. Results of this study show the feasibility of P. sinese in accumulating Cd and provide support for its application in remediation of soil moderately contaminated by Cd.

Plant Induced Changes to Rhizosphere Characteristics Affecting Supply of Cd to Noccaea caerulescens and Ni to Thlaspi goesingense.

Changes in soil rhizosphere properties after growing the Cd hyperaccumulator Noccaea caerulescens and the Ni hyperaccumulator Thlaspi goesingense were investigated. Dissolved organic carbon content increased in the rhizosphere, but there were no significant changes in the solution concentrations of Cd and Ni. Concentrations of these metals extracted by NH4Cl and EDTA decreased in the rhizosphere, as did DGT-measured concentrations, indicating a depletion of labile metal in the solid phase. The results could be explained by the increased DOC in the rhizosphere maintaining a higher proportion of the labile metal in solution through complexation, with the overall depletion of metals only manifest in the solid phase. The DGT induced fluxes in soils and sediments (DIFS) model was used to provide key kinetic information on soil processes and labile pool size. These data showed that the more limited metal supply in the rhizosphere after the growth of hyperaccumulators was due to both depletion of the solid phase pool and a lower rate constant of supply from solid phase to solution. The effect on the rate constant, which could be rationalized by the plant sequentially accessing and consuming the more labile pools of metal, was most marked for Cd, which had the highest accumulation factors.