Total Cd Uptake Research Articles

Effects of soil water content on Cd immobilization and uptake by leek with the combined application of biochar and organic fertilizer.

This study investigated the effects of soil water content on Cd immobilization and uptake by leek with the combined application of biochar and organic fertilizer using mechanism experiment and pot experiment. Mechanism experiment was conducted with the three-layer mesh method, which can reveal the individual mechanisms and contributions of biochar and soil to Cd immobilization. The results of mechanism experiment showed that the Cd adsorption amount by biochar was very little at low soil water content (θw = 20%, w/w), and both of Cd adsorption amount and rate significantly increased at higher θw (40% and 60%). The Cd immobilization by biochar at higher θw (40% and 60%) was significantly better than that at low θw (20%) in soils because F1 (percentages of exchangeable Cd) decreased with increasing moisture. For example, the F1 percentages were 58.27%, 40.67%, and 38.46% in the soil at 4.40mg·kg-1 under M20, M40, and M60 (θw = 20%, 40%, 60%) at day 120, respectively. The results of pot experiment showed that the Cd in leek leaves and roots continuously accumulated with planting time in each batch, and biochar and organic fertilizer treatments significantly reduced the Cd enrichment in leek. Combined treatment of biochar and organic fertilizer (BO) is superior to biochar treatments (BC) and CK for Cd immobilization in soil. For example, the percentages of F1 under the treatments of CK, BC, and BO were 64.43%, 49.13%, and 43.67% at 75% field water capacity treatment, respectively. For the same treatment, with increasing water contents, the better the Cd was immobilized in the soil and the greater the leek biomass. However, the total uptake of Cd by leek were increased by promoting crop growth under water content conditions.

Coupling electrokinetic remediation with ryegrass for the synergistic remediation of Cd and C14 alkane co-contaminated soil

Electrokinetic coupled with phytoremediation (EKPR) is an innovative technology to remediate heavy metals or petroleum hydrocarbons polluted soils. However, the feasibility and mechanism of EKPR remediation heavy metals and petroleum hydrocarbons co-contaminated soil are still unknown. This study evaluated the feasibility and potency of coupling EK remediation with Lolium perenne L. (ryegrass) (EKRG) in remediating the cadmium (Cd) and C14 alkane co-contaminated soil. The ryegrass biomass, Cd uptake amount, C14 alkane removal and soil bacterial community were determined for different soil sections of the EKRG treatment. Results indicated that the polarity reversal direct current electric field increased the total Cd uptake amount of ryegrass to 17.95 μg, most likely due to an increase of 41.7 % of the ryegrass shoot biomass. The ryegrass shoots, in the initial anode section of EKRG treatment, acquired an increment in biomass by 82.1 % and Cd uptake amount by 67.1 %, corresponding to 1.02 g and 7.76 μg, respectively. The EKRG treatment boosted the removal of C14 alkane in comparison with the mono-treatment of ryegrass or EK, i.e., increasing by 28.4 % and 36.5 %, respectively. Microbial community analysis suggested that the EKRG treatment promoted the relative abundances of hydrocarbons degrading bacteria, potentially responding to the enhanced removal of C14 alkane. Further, the correlation analysis showed that the removal of C14 alkane was positively correlated with the ryegrass biomass and Cd uptake amount in the EKRG treatment, which again validated that the addition of electric field benefited the remediation of Cd and the removal of C14 alkane. These results together indicated that the electric field assisted phytoremediation would be an effective approach for remediating the Cd and C14 alkane co-contaminated soils.

Changes in Soil Chemical Properties and Rhizosphere Bacterial Community Induced by Soil Amendments Associated with Reduction in Cadmium Accumulation by Rice

Soil amendments have been extensively employed for the purpose of remediating soils contaminated with cadmium (Cd). However, the potential impacts of soil amendments on soil chemical properties, soil Cd bioavailability, total Cd accumulation by rice, and rhizosphere bacterial community in Cd-contaminated paddy fields located in a tropical region is still at its infancy. In this study, a commercial MgO-CaO-SiO2 conditioner (A), biochar (B), and a combination of the commercial MgO-CaO-SiO2 conditioner and biochar with a ratio of 1:1 (C) were applied at two different doses [2250 kg ha−1 (A150, B150, C150), 4500 kg ha−1 (A300, B300, C300)] to investigate their impacts on soil Cd stabilization and total Cd uptake of rice straw and grain in a Cd-contaminated remediation field experiment. Rhizosphere bacterial community diversity and composition were also assessed using high-throughput sequencing based on 16S rRNA genes. Compared with non-amendment treatment (CK), soil pH, cation exchange capacity (CEC), organic matter (OM), total nitrogen (TN), available nitrogen (AN), and nitrate (NO3−) concentrations were significantly elevated, whereas ammonium (NH4+) and soil available Cd concentrations were reduced by soil amendment treatments. Meanwhile, soil amendments significantly decreased concentrations of total Cd in both rice straw and grain, with the lowest Cd concentration in the C300 treatment. Soil pH and CEC were significantly and negatively associated with soil Cd availability and rice straw and grain Cd concentrations, while NH4+ concentration was positively correlated with soil available Cd concentration, and OM, TN, and NO3− concentrations were positively linked with rice grain Cd concentration. Soil amendments significantly increased bacterial Chao 1 and Shannon indexes and altered bacterial community composition in rhizosphere soil, due to changes in the composition of the community primarily influenced by variations in soil pH, CEC, and soil available Cd, NH4+, available phosphorous (AP) and available Potassium (AK) concentrations. Furthermore, the abundant bacterial species (Pseudomonas) and rare bacterial species (Bacillus, Candidatus_Solibacter and Streptomyces) have been up-regulated by different soil amendments, which might be in favour of soil Cd immobilization. A structural equation model also showed that soil amendments could improve bacterial diversity and change soil pH and CEC, which were conducive to hindering the removal and conversion of Cd. Overall, these results indicate that biochar-(MgO-CaO-SiO2) mixed amendments at high dosage exerted better performance compared with single application soil amendment A and B. The changes in soil chemical properties, available Cd content, and rhizosphere bacterial community assembly induced by soil amendments are closely correlated with the decrease in rice’s ability to accumulate Cd.

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 Reduction in Spring Wheat: Root Exudate Composition Affects Cd Partitioning Between Roots and Shoots

Cadmium (Cd) in cereals is one of the major sources of Cd intake by human diets, and solutions to reduce Cd concentrations in wheat still need to be developed. Plant breeding, by selecting low-Cd varieties, can be an important tool to reduce Cd in crops. Knowing the genotypic variation in Cd accumulation and furthering our understanding of the impact of root exudates composition on Cd accumulation in crops may provide valuable information for plant breeding. In this study, we selected nine spring wheat varieties and analysed the accumulation and distribution of Cd in shoots, roots, root surfaces and kernels in relation to their qualitative and quantitative composition of root exudates, determined by 1H-NMR (Proton Nuclear Magnetic Resonance). Results showed that the Cd concentration in shoots at an early stage could be used as a predictor for Cd concentration in kernels. Total Cd uptake was not correlated to the mobility of Cd in the rhizosphere, but total Cd was negatively correlated to Cd adsorbed at the root surface. Furthermore, (i) exudation of organic acids (primarily succinate and acetate) increased Cd concentration in shoots, and (ii) exudation of nucleosides, DNA (deoxyribonucleic acid) degradation products, increased Cd adsorption at the root surface. Therefore, root exudates composition should be taken into account when selecting for low-Cd wheat traits.

Combined effects of zinc oxide nanoparticles and melatonin on wheat growth, chlorophyll contents, cadmium (Cd) and zinc uptake under Cd stress

Zinc oxide nanoparticles (ZnONPs) and melatonin (MT) have been known to regulate heavy metal toxicities in plants in some studies, the effect of their combined use on cadmium (Cd) uptake by wheat (Triticum aestivum L.) and underlying mechanisms is largely unknown. Thus, plant growth, uptake and translocation of Cd mediated by soil applied ZnONPs and foliar applied MT were investigated in wheat grown in Cd polluted soil under ambient conditions. The results depicted that ZnONPs stimulated the growth, chlorophyll contents, and yield of wheat in a dose additive way and this effect was further increased with foliar application of MT. 100 mg/kg of ZnONPs alone enhanced the grain yield by 60.5 % and this increase was about 177.5 % under combined ZnONPs and 100 μM MT treatment. ZnONPs treatments decreased Cd concentration whereas increased zinc (Zn) concentrations in shoots, roots, husks and grains and the effect was further increased with exogenous MT combined with NPs in a dose-additive way. 50 and 100 mg/kg ZnONPs treatments alone decreased grain Cd by 6.5 %, and 20 % and increased the Zn concentration by 20.1 % and 24 % than control. 100 mg/kg ZnONPs +100 μM MT treatment decreased the grain Cd by 63.5 % and increased grain Zn by 51 % than control treatment. Total Cd uptake (tissues biomass × Cd concentration in respective tissues) in shoots, roots, husks and grains increased with ZnONPs alone or combined with MT than control whereas soil post-harvest bioavailable Cd concentration decreased with treatments than control. The Cd reduction in grains was due to increase in biomass and Zn concentration thereby decreasing bioavailable Cd in soil and its accumulation in plants. This study suggested that combined use of ZnONPs and MT may provide new approaches for minimizing Cd and biofortification of Zn in edible parts of plants.

Field-scale remediation of cadmium-contaminated farmland soil by Cichorium intybus L.: Planting density, repeated harvests, and safe use of its Cd-enriched biomass for protein feed

Chicory ( Cichorium intybus L.) is a perennial herb cultivated worldwide that has a wide range of industrial uses, produces large yields, and also has strong cadmium (Cd) accumulation ability. In field experiments in two farmlands with acidic soils, chicory potential to remove Cd from contaminated soils was evaluated at different planting densities and with repeated harvesting. To determine whether Cd-contaminated biomass could be used as a feed ingredient, efficacy of detoxification was measured with successive extractions using different concentrations of HCl. Biomass per plant decreased with an increase in planting density, and maximum biomass per plant in the two experimental fields was 17.11 and 13.89 g·plant −1 . However, the increase in plant numbers at high planting density increased total biomass per hectare, and maximum accumulated biomass at the highest planting density in the two experimental fields was 14,226 and 22,020 kg·ha −1 . The highest Cd concentrations were at the first harvest and were 27.68 and 19.27 mg·kg −1 Cd in the two fields, resulting in bioconcentration factors (BCFs) of 24.94 and 24.39, respectively. With the increase in number of harvests, aboveground Cd concentrations and BCFs decreased. Planting density had no consistent effect on aboveground Cd concentrations at the first two harvests, whereas Cd concentration decreased gradually with the increase in density at the last three harvests. Collectively, after five repeated harvests, total Cd uptake was highest at the highest planting density, reaching 237.55 g·ha −1 (field 2), and the corresponding phytoextraction efficiency was 11.57%. Two consecutive extractions with 0.5% HCl removed 96.30% of Cd in leaf meal, which reduced Cd concentration below the threshold for feed safety while retaining most of the crude protein, there remained a substantial crude protein content with 173.1 g·kg −1 . Thus, biomass of forage crops used for phytoremediation may also provide economic gain. • Phytoextraction efficiency of chicory was not inferior to that of hyperaccumulators. • High planting density and repeated harvesting promote Cd phytoextraction. • Two consecutive extractions with 0.5% HCl removes 96.30% of Cd in biomass. • Protein from leaf after Cd extraction can be a potential source of feed protein.

Continuously applying compost for three years alleviated soil acidity and heavy metal bioavailability in a soil-asparagus lettuce system.

Soil acidification and heavy metal pollution are two common barrier factors threatening plant growth and agro-product quality. Applying manure compost is promising to alleviate soil acidity, while it may increase heavy metal accumulation in soil. In a 3-year field experiment, compost was applied for 12 consecutive harvest seasons at 15, 30, and 45 t ha−1 in a slightly acidic soil. Samples were taken at the twelfth season to examine the changes of soil properties, vegetable productivity, heavy metal accumulation and bioavailability in the soil-asparagus lettuce system. The results showed that the pH values of the topsoil were increased by 0.49–0.75 units in compost added soils compared with no compost control, soil organic matter (SOM) contents and cation exchange capacity (CEC) were increased by 34–101% and 43–44%, respectively. The soil nutrient contents were also increased in compost treatments. Continuously applying compost increased Cd, Cu, and Zn concentrations in topsoil by up to 32, 20, and 22% and decreased Pb by 10%, while soil available Cd and Zn concentrations were reduced by up to 54 and 86%, and available Cu was increased by 19–63%. The biomass of asparagus lettuce was increased by 30–59% in compost treatments, with Cd and Zn concentrations in the plant tissues reduced by 28–50% and 14–67%. Cu concentrations in the lettuce shoots were increased by 20–39%. The concentration factor and total uptake of Cd and Zn in lettuce were effectively reduced in compost treatments. Cd was more prone to be taken up, translocated and accumulated from soil to the lettuce plant than the other heavy metals. Continuously applying compost over 3 years increased soil pH, SOM, CEC, nutrient contents, and lettuce productivity, decreased Cd and Zn bioavailability in the soil-lettuce system, while posing a risk of increasing heavy metal accumulation in topsoil.

Two plant growth-promoting bacterial Bacillus strains possess different mechanisms in affecting cadmium uptake and detoxification of Solanum nigrum L.

Microorganisms affect cadmium (Cd) extraction by hyperaccumulators to varying degrees, but the potential mechanism has not been completely studied. Here, two plant growth-promoting bacteria (PGPB, Bacillus paranthracis NT1 and Bacillus megaterium NCT-2) were assessed for their influence on Cd uptake by Solanum nigrum L. and their influence mechanisms. The results showed that both two strains could regulate phytohormones secretion, alleviate oxidative stress and promote S. nigrum growth when exposed to Cd (dry weight was significantly increased by 21.51% (strain NCT-2) and 21.23% (strain NT1) compared with the control, respectively). Additionally, strain NCT-2 significantly elevated the translocation factor (TF) and bioconcentration factor (BCF), and thus significantly facilitated total Cd uptake by 41.80% of S. nigrum, whereas strain NT1 significantly reduced the BCF and TF, resulting in insignificant effect on total Cd uptake of S. nigrum compared with the control. Results of qPCR illustrated that the two strains influenced the detoxification of Cd in S. nigrum by affecting the expression of antioxidant enzyme genes and gene PDR2. Moreover, the differential expression of heavy metal transport genes IRT1 and HMA may lead to the difference of Cd accumulation in S. nigrum. Principal component analysis and Pearson correlation coefficient analysis further verified the positive roles of salicylic acid and indole-3-acetic acid on Cd detoxification of S. nigrum, and the positive correlation relationship between transportation of Cd from underground to shoot, plant biomass and Cd uptake. Altogether, our results demonstrated that these two PGPB have great potential in helping plants detoxify Cd and could provide insights into the mechanism of PGPB-assisted phytoremediation of Cd-contaminated soil.

Deciphering distinct root exudation, ionomics, and physio-biochemical attributes of Serratia marcescens CP-13 inoculated differentially Cd tolerant Zea mays cultivars.

Cadmium (Cd) being a non-essential, mobile, and toxic heavy metal, negatively affects the plant growth and physiology. Current work investigated the impact of Serratia marcescens CP-13 inoculation on root organic acids and nutrient exudates of two maize cultivars varying in Cd tolerance under induced Cd toxicity. Seedlings of Cd-sensitive (Sahiwal-2002) and Cd-tolerant (MMRI-Yellow) cultivars were grown either inoculated or non-inoculated with CP-13 in Petri plates having various Cd stress levels (0, 6, 12, 18, 24, 30μM). Seedlings were transferred to rhizoboxes for the collection of root exudates and analysis of physio-biochemical traits. Both maize cultivars exuded higher organic acids and nutrient exudates under non-inoculated conditions as compared to inoculated ones. Non-inoculated tolerant cultivar exhibited higher nutrient accumulation, biomass, antioxidants, total chlorophyll, Cd release meanwhile reduced Cd uptake, lipid peroxidation, exudation of organic acids, and nutrients than the sensitive one. However, under CP-13 inoculation, Cd sensitive cultivar exhibited less exudation of organic acids (citric acid, acetic acid, malic acid, glutamic acid, formic acid, succinic acid, and oxalic acid), nutrients mobilization (K, Na, Zn, Ca, and Mg), total chlorophyll, antioxidants (APX, SOD, POD), total soluble sugar, diminished MDA, and Cd uptake. The significant reduction in release of root exudates by both cultivars was likely due to the plant growth promoting traits of CP-13 which confer Cd tolerance. The maximum release of rhizospheric root exudates were documented at 30μM applied Cd stress. Therefore, the Serratia sp. CP-13 was proposed as a potential inoculant for bioremediation of Cd together with maize cultivars.

Identifying adsorption sites for Cd(II) and organic dyes on modified straw materials

Turning agricultural waste into effective remediation materials is a highly promising approach for reducing in-field crop burning and promoting affordable wastewater treatment. This comparative study aims to identify active adsorption sites for methylene blue (MB), crystal violet (CV), and cadmium (Cd) as model pollutants on wheat straw materials modified by a thermal partial-oxidation process. The optimal modification temperature was found to be 160–180 °C for MB and CV adsorption, which is much lower than that of Cd(II) at 220–240 °C. A strong linear correlation exits between total surface group concentrations and Cd(II) uptake, indicating that both acidic and basic functional groups are favourable adsorption sites of Cd(II). By contrast, basic groups generated at higher modification temperatures might have adverse effects on MB and CV adsorption. These results provided mechanistic insights and predictive approach into reuse of agricultural waste for environmental remediation.

Cadmium Uptake and Growth Responses of Potted Vegetables to the Cd-Contaminated Soil Inoculated with Cd-Tolerant Purpureocillium lilacinum N1

Bioremediation of Cd- (cadmium) contaminated soil using Cd-tolerant fungus is considered an eco-friendly and cost-effective technique. In this study, we isolated one fungal strain that was hyper-tolerant to Cd from a highly polluted river and conducted pot experiments to evaluate its effects on bioremediation. We found that the fungal strain belonging to the genus, Purpureocillium lilacinum, tolerated 12,000 mg/L Cd. SEM manifested that Cd can be bioaccumulated on the crumpled mycelial surface, generating plenty of metal precipitation particles. In addition, pot experiments showed that the inoculation of P. lilacinum N1 could reduce the total Cd content in soil (2.09% in low contaminated soil and 12.56% in high contaminated soil) and greatly promote plant growth (2.16~3.13 times). Although the Cd concentration of plants was increased by 112.8% in low contaminated soil and decreased by 9.5% in highly contaminated soil with the inoculation of P. lilacinum N1, the total uptake of Cd by plants was greatly improved—1.84~3.6 times higher than that in CK groups. All our results suggest that P. lilacinum N1 is a valuable candidate for the bioremediation of Cd-contaminated soils because of its dual effects on the total Cd content in soil and Cd uptake in plants.

Zinc promotes cadmium leaf excretion and translocation in tall fescue (Festuca arundinacea)

Phytoexcretion is a novel strategy to remediate cadmium (Cd) pollution by leaf excretion in tall fescue (Festuca arundinacea), which involves the processes of Cd leaf excretion, root-to-leaf translocation, and root uptake. A hydroponic experiment was designed to investigate a series of 11 zinc (Zn) concentrations on Cd leaf excretion in tall fescue under 75 μM Cd stress. The results showed that the promotions of Zn on Cd leaf excretion, root-to-leaf translocation, and leaf accumulation were concentration-dependent in tall fescue. Zn treatments at 90 and 135 μM resulted in the highest Cd leaf excretion with 118.1 and 123.6 mg/kg of Cd excretion amount and 27.0 and 26.6% of excretion ratio, which were 2.6 and 2.7 fold of the control (15 μM of Zn), respectively. Cd leaf excretion was decreased when Zn treatments reached 180 μM, which could be toxic to plants as indicated by the decline of plant biomass. Zn also promoted leaf Cd accumulation and Cd translocation from roots to leaves and reached the highest at 90 and 180 μM respectively. Root Cd accumulation decreased with the increase of Zn concentrations, but the total plant Cd uptake did not decrease significantly until Zn concentration reached 90 μM. Our results indicate that 90 μM of Zn treatment can be served as the threshold to promote Cd leaf excretion and improve the efficiency of Cd phytoexcretion in tall fescue.

Cadmium-resistant and arginine decarboxylase-producing endophytic Sphingomonas sp. C40 decreases cadmium accumulation in host rice (Oryza sativa Cliangyou 513)

In this study, an cadmium (Cd)-immobilizing and arginine decarboxylase-producing endophytic Sphingomonas sp. strain C40 obtained from the seeds of Oryza sativa Cliangyou 513 was characterized for its Cd availability and Cd uptake in host rice using hydroponic and soil experiments. The Cd concentration decreased by 51–95% compared to the control, while the spermidine concentration increased by 19–25% with Cd compared with no Cd in the strain C40-inoculated solution. Strain C40 decreased the above-ground tissue Cd content by 27–37% and increased spermine and spermidine contents by 28–67% and the expression levels of genes involved in spermine and spermidine production by 29–217% in rice roots compared to the controls. Furthermore, correlation analyses showed the significantly negative correlation between rice root spermine and spermidine contents and above-ground tissue Cd content. In the Cd-added soil, strain C40 promoted the rice biomass by 29–36% and decreased rice root, above-ground tissue, and grain Cd contents by 18, 16, and 33% and total grain Cd uptake by 14% compared with the controls at the maturity stage. Strain C40 decreased the exchangeable Cd content by 27% and increased the Fe and Mn oxides-bound Cd content by 45% in the rice rhizosphere soils at the maturity stage compared with the controls. These results suggested that the endophytic bacterial strain C40 increased rice root polyamine production and their related gene expression and the transformation of available Cd to unavailable Cd, leading to reduced Cd accumulation and translocation from the rice roots to grains.

Cadmium phytoextraction by Helianthus annuus (sunflower), Brassica napus cv Wichita (rapeseed), and Chyrsopogon zizanioides (vetiver)

The use of phytoextraction plant species to accumulate soil metals into harvestable plant parts is a method used for managing soils with high cadmium (Cd). We evaluated three Cd accumulating species recently recommended for such use in cacao farms where Cd removal is needed to maintain markets: Helianthus annuus (sunflower), Brassica napus (rapeseed), and Chyrsopogon zizanioides (vetiver). Plants were grown in two greenhouse pot experiments with different Cd-spiked growth media: (sand plus perlite) and a natural soil. Plant total Cd and Cd uptake in shoot biomass of all species, across both experiments, increased linearly with increasing amounts of added Cd. Rapeseed had the highest plant total Cd and sunflower had the highest Cd uptake in shoot biomass. The highest application of Cd corresponded to the highest plant total Cd and shoot biomass Cd uptake, regardless of species. The bioconcentration factor (BCF) for each species increased in a curvilinear manner with added Cd, with maximum BCF values for plants grown in the sand and perlite matrix at 2.5 mg kg−1 added Cd and in the natural soil at 5.0 mg kg−1 added Cd. We conclude that the Cd uptake (shoot biomass only) capability of the three species examined is greatest for sunflower given its increased uptake with Cd additions, its BCF value > 1, and lack of observed visual Cd toxicity symptoms, fungus and insect damage. Although these species had BCF >1, the potential annual removal of Cd would have been too small to support a meaningful phytoextraction practice.

Effects of Burkholderia sp. D54 on growth and cadmium uptake of tomato, ryegrass and soybean plants

Cadmium (Cd) contamination of agricultural soil is a serious global problem. Plant growth-promoting bacteria could modulate growth and Cd uptake of plants. In this study, the effects of rhizobacterium Burkholderia sp. D54 on growth and Cd uptake of tomato, ryegrass and soybean plants were investigated. The bacterial inoculation increased at least one pigment content of all tested plants. In soybean plants, chlorophyll a, chlorophyll b and carotenoid concentrations were increased by 63.19%, 73.15% and 57.58%, respectively. The dry mass of aerial parts was increased by 67.38%, 19.13% and 67.41% in tomato, ryegrass and soybean plants, respectively. The total Cd uptake in tomato and ryegrass plants was increased upon bacterial inoculation, while the Cd concentration varied among plant species. Burkholderia sp. D54 inoculation decreased Cd concentration in aerial parts of tomato and Cd translocation from roots to aerial parts (p < 0.05). The Cd concentration in roots and aerial parts of ryegrass was increased, and Cd translocation from roots to aerial parts was enhanced. By contrast, Cd concentration in aerial parts and roots of the soybean plants was decreased. Burkholderia sp. D54 also modulated the nutrient uptake of the tested plants. The K, Ca and Zn concentrations were decreased in tomato and soybean but enhanced in ryegrass. These results indicated that Burkholderia sp. D54 could modulate growth, nutrient element concentration and Cd uptake of the tested plants. This study might provide a promising way of using PGPR control Cd uptake in food crops or assisting phytoremediation by hyperaccumulators.

Distribution and accumulation of inorganic elements in Ligusticum chuanxiong

Aiming at the phenomenon of heavy metal Cd exceeding the standard of Chuanxiong medicinal materials,the accumulation of 12 inorganic elements,including heavy metals,in Ligusticum chuanxiong was studied in this paper. It was found that the contents and distribution of most inorganic elements in the stems and leaves of L. chuanxiong were higher than those in the rhizomes at seedling and shooting stages. The content of most elements in rhizome reached the highest at harvest stage,and the distribution ratio of some elements in rhizome was higher than that in stem and leaf at harvest stage. But rhizome,stem and leaf of L. chuanxiong have relatively stable absorption capacity and enrichment effect on different elements,and are less affected by growth period and position. Rhizomes and stems and leaves of L. chuanxiong were enriched with Cd,and stems and leaves also accumulated Pb at seedling stage and stem stage. The absorption capacity of Pb in stems and leaves of L. chuanxiong was higher than that of rhizomes,and the ability of absorbing Cd was less than that of rhizomes at harvest time. The total uptake of Cd and Pb by L. chuanxiong decreased with the prolongation of growth time,but the proportion of Cd and Pb in rhizome increased,so that the content of Cd and Pb increased with the prolongation of growth time.

Residual effect of cadmium applications in different crop rotations and environments on durum wheat cadmium accumulation

Cadmium (Cd) is one of the heavy metals commonly present in soils that is toxic for living organisms and carcinogenic in humans. The uptake of Cd by a crop depends on various factors such as soil properties, plant-soil interaction, fertilizer management, and previous crop. The aim of the present study was to evaluate the residual effect of three Cd rates applied in three preceding crops (durum wheat [Triticum turgidum L. var durum], white lupine [Lupinus albus L.], and narrow-leafed lupine [Lupineus angustifolius L.]) on total dry matter, grain yield, and Cd concentration and uptake in three durum wheat cultivars in four environments. The residual effect of a cadmium chloride (CdCl2) dose applied in the preceding crop to durum wheat was affected by location and previous crop, with the greatest effect in La Serena with narrow-leafed lupines as the preceding crop. Finally, in soils where a critical level of Cd is present, narrow-leafed lupines should not be used as a previous crop to durum wheat.

Cadmium (Cd) concentration in wheat (Triticum aestivum) grown in Cd-spiked soil varies with the doses and biochar feedstock

Biochar is considered a promising amendment for the reduction of metal concentration in plants; however, the effects of biochar in terms of dose and feedstock on metal uptake by plants remain widely unclear. In the current study, three individual biochars were prepared at 450 °C from different feedstocks (wheat straw, sukh chain (Pongamia pinnata), and cotton sticks). The main aim was to evaluate their ability to remediate cadmium (Cd)-spiked soil in terms of growth response and Cd uptake by wheat (Triticum aestivum) tissues. Biochars were separately applied at 0, 1, and 2% (w/w) in Cd-spiked soil and wheat was grown until maturity in pots and then morphological and physiological parameters and Cd concentrations in grains, roots, and shoots were determined. The post-harvest soil was analyzed for extractable Cd concentrations. Plants grown in Cd-spiked soil treated with biochars had higher seed germination, lengths of roots, shoots, and spikes, grains per spike and leaf relative water contents, chlorophyll contents, and dry weight of roots, shoots, and grains as compared to the untreated control. Biochar treatments significantly decreased the Cd concentrations in shoots, roots, and grains as well as total Cd uptake by grains. Soil extractable Cd concentrations were significantly decreased with biochar treatments. The application of 2.0% wheat straw biochar was the most efficient treatment in increasing grain yield and decreasing Cd in grains as well as soil extractable Cd than the other two biochars and doses applied.

Low root/shoot (R/S) biomass ratio can be an indicator of low cadmium accumulation in the shoot of Chinese flowering cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) cultivars.

Chinese flowering cabbage is a commonly consumed vegetable that accumulates Cd easily from Cd-contaminated soils. Cultivations of low-Cd cultivars are promising strategies for food safety, but low-Cd-accumulating mechanisms are not fully elucidated. To address this issue, 37 cultivars were screened to identify high- and low-Cd cultivars upon exposure to sewage-irrigated garden soil pretreated with different Cd concentrations (1.81, 2.90, and 3.70mgkg-1dry soil). The results showed that shoot Cd concentrations differed among the cultivars by maximum degrees of 2.67-, 3.71-, and 3.00-fold under control and treatments, respectively. Soil-pot trial and hydroponic trial found no significant difference in Cd and Ca mobilization, uptake, and transport ability by root per weight between high- and low-Cd cultivars. Interestingly, a stable R/S ratio difference among cultivars (p < 0.01) was observed, and the cultivar variation of Cd accumulation in shoots was mainly dependent on their R/S ratios. R/S ratio was also statistically positively associated with Cd and Ca accumulation in high- and low-Cd cultivars (p < 0.05), both in soil and hydroponics culture. This was mainly due to the lower root biomass of low-Cd cultivars resulted in lower total release of root exudates, lower total Cd and Ca mobilization in rhizosphere soil, and lower total Cd and Ca uptake and transport. The higher shoot biomass of low-Cd cultivars also has dilution effects on Cd concentration in shoot. Overall, low R/S ratio may be regarded as a direct and efficient indicator of low Cd accumulation in the shoot of Chinese flowering cabbage. These findings provided the possibilities to screening low-Cd cultivars using their R/S ratio.