Remediation Of Cd-contaminated Soils Research Articles

Cadmium phytoremediation potential of Houttuynia cordata: Insights from growth, uptake, and rhizosphere mechanisms

Cadmium (Cd) pollutes 7.0 % of China’s land area. This study examined the potential of Houttuynia cordata for Cd phytoremediation because of its ability to accumulate Cd in its growth matrix. H. cordata were planted in plastic pots filled with paddy field soils having low (LCd), medium (MCd), and high (HCd) Cd levels of 0.19, 0.69, and 2.91 mg/kg, respectively. After six months of growth, harvested plant parts were evaluated for Cd uptake and tolerance mechanisms. Metabolomics and metagenomics approaches were employed to investigate the soil rhizosphere mechanism. Results showed that the average plant biomass increased as soil Cd increased. The biomass Cd contents surpassed the allowable Cd limits for food (≤ 0.2 mg/kg) and medicinal uses (≤ 0.3 mg/kg). Cd contents were higher in H. cordata roots (30.59–86.27 mg/kg) than in other plant parts (0.63–2.90 mg/kg), with significantly increasing values as Cd soil level increased. Phenolic acids, lipids, amino acids and derivatives, organic acids, and alkaloids comprised the majority (69 in MCd vs HCd and 73 % in LCd vs HCd) of the shared upregulated metabolites. In addition, 13 metabolites specific to H. cordata root exudates were significantly increased. The top two principal metabolic pathways were arginine and proline metabolism, and beta-alanine metabolism. H. cordata increased the abundance of Firmicutes and Glomeromycota across all three Cd levels, and also stimulated the growth of Patescibacteria, Rozellomycota, and Claroideoglomus in HCd. Accordingly, H. cordata demonstrated potential for remediation of Cd-contaminated soils, and safety measures for its production and food use must be highly considered.

The immobilization of cadmium by rape straw derived biochar in alkaline conditions: Sorption isotherm, molecular binding mechanism, and in-situ remediation of Cd-contaminated soil

The issue of cadmium (Cd) contamination in alkaline soils is escalating, necessitating the prompt implementation of effective passivation strategies. Biochar has gained significant attention for its potential in immobilizing heavy metals; however, the suitability of biochar as a remediation material and its micro-scale interaction mechanisms with Cd under alkaline conditions remain unclear. Rape straw (RS) were pyrolyzed at 400 °C (RB400) and 700 °C (RB700) to produce biochar. Adsorption and soil incubation experiments were carried out to assess the feasibility of using rape straw derived biochar pyrolyze at different temperatures and understanding their remediation mechanisms in alkaline environments. The sorption capacity for Cd immobilization was evaluated using sorption isotherms, revealing that RB700 exhibited enhanced Cd sorption performance with a maximum sorption capacity of 119.33 mg g−1 calculated from the Langmuir isotherm equation at pH 8. Cd L3-edge X-ray absorption near-edge structure (XANES) spectroscopy analysis confirmed that the dominant sorption species of Cd were organic Cd in RB400, with CdCO3 precipitation increased to 73.9% in RB700. Solid-state 13C nuclear magnetic resonance (13C-NMR) spectroscopy demonstrated that aromatic and carboxyl C functional groups are involved in the organic sorption of Cd through complexation and Cd2+-π interactions in alkaline solutions. The precipitation of CdCO3 in RB700 may resulted in a more effective passivation effect compared to RB400, leading to a significant 15.54% reduction in the DTPA-Cd content in Cd-contaminated soil. These findings highlight the effective Cd passivation Cd in alkaline environments by rape straw derived biochar, providing new molecular insights into the Cd retention mechanism of biochar. Furthermore, it presents novel ideas for improving remediation approaches for alkaline Cd-contaminated soils.

Remediation of cadmium-contaminated soil by biochar-loaded nano-zero-valent iron and its microbial community responses

At present, cadmium (Cd)-contaminated soil has been increasingly serious, which is adverse to soil health. In this study, biochar (BC) and biochar-loaded nanoscale zero-valent iron (nZVI@BC) were synthesized for remediation of Cd-contaminated soil. The effects of various factors including reaction time, dosage, nZVI loading on Cd fractionation, soil available iron, pH, CEC, and soil enzyme activity were comprehensively discussed. It can be concluded that nZVI@BC exhibited more excellent immobilization effect of Cd, and was positively correlated with dosage and reaction time, but negatively related to nZVI loading. As a result, 5% nZVI@BC(1:3) performed the best. Soil available iron, pH, and CEC were significantly enhanced with increasing nZVI loading. The immobilization mechanism was analyzed, including ion exchange, physical adsorption, surface complexation, electrostatic attraction as well as co-precipitation. Besides, nZVI@BC remarkably promoted soil catalase activity, but inhibited urease and FDA hydrolase activities. Furthermore, the effects and differences on the diversity, abundance, and species composition of soil microbial communities were deeply explored. The order of bacterial community richness in each group was CK > Cd > BC > nZVI@BC, and the bacterial community diversity was CK > nZVI@BC > Cd > BC. The greatest difference of species abundance composition was observed between nZVI@BC treatment group and the control. Additionally, forty-three biomarkers were screened, which primarily belonged to Proteobacteria, Gemmatimonadetes, Firmicutes, and Actinobacteria. This study will provide the profound theoretical basis for nZVI@BC remediation of Cd-contaminated soil and its microbial community responses.

Enhancing soil redox dynamics: Comparative effects of Fe-modified biochar (N–Fe and S–Fe) on Fe oxide transformation and Cd immobilization

Biochar and modified biochar have gained wide attention for Cd-contaminated soil remediation. This study investigates the effects of rape straw biochar (RSB), sulfur-iron modified biochar (S–FeBC), and nitrogen-iron modified biochar (N–FeBC) on soil Fe oxide transformation and Cd immobilization. The mediated electrochemical analysis results showed that Fe modification effectively enhanced the electron exchange capacity (EEC) of biochar. After 40 days of anaerobic incubation, compared to the treatment without biochar (CK), the concentrations of CaCl2-extractable Cd in N–FeBC, S–FeBC, and RSB treatments decreased by 79%, 53%, and 23%, respectively. Compared with S–FeBC, N–FeBC significantly decreased the soil Eh and increased soil pH within the first 15 days, which could be attributed to its higher EEC and alkalinity. There is a negative correlation between the concentration of CaCl2-extractable Cd and soil pH (p < 0.01). The sequential extraction results showed that both N–FeBC and S–FeBC promoted Cd transfer from acid-soluble to Fe/Mn oxides bound fraction (Fe/Mn–Cd). N–FeBC significantly increased the concentration of amorphous Fe oxides (amFeox) from 4.0 g kg−1 in day 1 to 4.6 g kg−1 in day 15 by promoting the NO3−-reducing Fe(II) oxidation process, while S–FeBC significantly increased amFeox from 4.0 g kg−1 in day 15 to 4.8 g kg−1 in day 40 by promoting the Fe(II) recrystallization. There is a positive correlation between the concentration of amFeox and Fe/Mn–Cd (p < 0.01). The scanning electron microscopy analysis showed that Cd was bound to the amFeox coating on the surface of Fe-modified biochar. By acting as an electron shuttle, the active surface of Fe-modified biochar may serve as a hotspot for Fe transformation, which promotes amFeox formation and Cd immobilization. This study highlights the potential of Fe-modified biochar for the remediation of Cd-contaminated soils and provides valuable insights into the development of effective remediation approaches for Cd-contaminated soils.

Copper-dependent control of uptake, translocation and accumulation of cadmium in hyperaccumlator Sedum alfredii

Cadmium (Cd) is detrimental to plant growth and threatens human health. Here, we investigated the potential for remediation of Cd-contaminated soil with high copper (Cu) background using Cd hyperaccumulator ecotype (HE) Sedum alfredii. We assessed effects of Cu on Cd accumulation, compartmentation and translocation in HE S. alfredii, and compared with those in a related non-accumulator ecotype (NHE). We found that Cu supply significantly induced Cd accumulation in roots and shoots of long-term soil-cultivated HE S. alfredii. A large fraction of root Cd was accumulated in the organelles, but a small fraction was stored in the cell wall. Importantly, Cu addition reduced Cd accumulation in the cell wall and the organelles in root cells. Furthermore, leaf cell capacity to sequestrate Cd in the organelles was greatly improved upon Cu exposure. We also found that genes involving metal transport and cell wall remodeling were distinctly regulated to mediate Cd accumulation in HE S. alfredii. These findings indicate that Cu-dependent decrease of root cell-wall-bound Cd, and stimulation of efflux/influx of organelle Cd transport in root and leaf cells plays a role in the dramatic Cd hyperaccumulation expressed in naturally survived HE S. alfredii.

Kitchen compost-derived humic acid application promotes ryegrass growth and enhances the accumulation of Cd: An analysis of the soil microenvironment and rhizosphere functional microbes

Phytoremediation is an environmentally friendly and safe approach for remediating environments contaminated with heavy metals. Humic acid (HA) has high biological activity and can effectively complex with heavy metals. However, whether HA affects available Cd storage and the Cd accumulation ability of plants by altering the soil microenvironment and the distribution of special functional microorganisms remains unclear. Here, we investigated the effects of applying kitchen compost-derived HA on the growth and Cd enrichment capacity of ryegrass (Lolium perenne L.). Additionally, the key role of HA in regulating the structure of rhizosphere soil bacterial communities was identified. HA promoted the growth of perennial ryegrass and biomass accumulation and enhanced the Cd enrichment capacity of ryegrass. The positive effect of HA on the soil microenvironment and rhizosphere bacterial community was the main factor promoting the growth of ryegrass, and this was confirmed by the significant positive correlation between the ryegrass growth index and the content of SOM, AP, AK, and AN, as well as the abundance of rhizosphere growth-promoting bacteria such as Pseudomonas, Steroidobacter, Phenylobacterium, and Caulobacter. HA passivated Cd and inhibited the translocation capacity of ryegrass. The auxiliary effect of resistant bacteria on plants drove the absorption of Cd by ryegrass. In addition, HA enhanced the remediation of Cd-contaminated soil by ryegrass under different Cd levels, which indicated that kitchen compost-derived HA could be widely used for the phytoremediation of Cd-contaminated soil. Generally, our findings will aid the development of improved approaches for the use of kitchen compost-derived HA for the remediation of Cd-contaminated soil.

Comparative efficacy of wheat-straw biochar and chicken-waste compost on cadmium contaminated soil remediation, reducing cadmium bioavailability and enhancing wheat performance under cadmium stress

Cadmium (Cd) pollution of soil and food crops is a widespread environmental issue caused by excessive industrialization, unsustainable urbanization, and intensive farming practices. Cd, a hazardous element, poses significant risks to agro-environmental sustainability, food safety, and human health. Using organic materials such as biochar and compost to stabilize Cd in contaminated soil is an environmentally benign and cost-effective strategy for remediating moderately to highly polluted soil. However, in response to the scarcity of comparative studies on biochar and compost efficacy, this research explores the impact of wheat-straw biochar and chicken waste compost on Cd-contaminated soil remediation. A greenhouse experiment using two application rates (1.5 % and 2.5 %) of biochar and compost in 10 mg kg−1 Cd-contaminated soil revealed significant (p≤0.05) effects. The 2.5 % compost application increased soil organic carbon (SOC) from 0.45 % to 0.85 %, while 2.5 % biochar enhanced soil pH from 7.1 to 7.7 and electrical conductivity (EC) from 0.33 to 0.44 dSm−1. Notably, 2.5 % biochar significantly reduced Cd bioavailability from 9.49 to 4.90 mg kg−1, root accumulation from 29.8 to 16.4 mg kg−1 and shoot translocation from 16.8 to 8.4 mg kg−1. This reduction was confirmed through translocation factor (51.5 %) and immobilization efficiency (48.4 %). Furthermore, 2.5 % biochar improved chlorophyll content (a, b, and total) and wheat morphological attributes under Cd stress in soil. Overall, higher rates of biochar (2.5 %) and compost (2.5 %) effectively mitigate Cd uptake, improve soil properties, and enhance physiological and morphological responses, suggesting their promise for sustainable soil management practices.

Inoculation of cadmium-tolerant bacteria to regulate microbial activity and key bacterial population in cadmium-contaminated soils during bioremediation

The perennial ryegrass Lolium perenne can be used in conjunction with cadmium (Cd)-tolerant bacteria such as Cdq4–2 (Enterococcus spp.) for bioremediation of Cd-contaminated soil. In this study, a theoretical basis was provided to increase the efficiency of L. perenne remediation of Cd-contaminated soil using microorganisms to maintain the stability of the soil microbiome. The experimental design involved three treatment groups: CK (soil without Cd addition) as the control, 20 mg·kg–1 Cd-contaminated soil, and 20 mg·kg–1 Cd-contaminated soil + Cdq4–2, all planted with L. perenne. The soil was collected on day 60 to determine the soil microbial activity and bacterial community structure and to analyze the correlation between soil variables, the bacterial community, available Cd content in the soil, Cd accumulation, and L. perenne growth. The soil microbial activity and bacterial community diversity decreased under Cd stress, and the soil microbial community composition was changed; while inoculation with Cdq4–2 significantly increased soil basal respiration and the activities of urease, invertase, and fluorescein diacetate (FDA) hydrolase by 83.65%, 79.72%, 19.88%, and 96.15% respectively; and the stability of the community structure was also enhanced. The Actinobacteriota biomass, the amount of available Cd, and the above- and belowground Cd content of L. perenne were significantly negatively correlated with the total phosphorus, total potassium, and pH. The activity of urease, invertase, and FDA hydrolase were significantly positively correlated with the biomasses of Acidobacteriota and L. perenne and significantly negatively correlated with the Chloroflexi biomass. Further, the available soil Cd content and the above- and belowground Cd levels of L. perenne were significantly positively correlated with the Actinobacteriota biomass and significantly negatively correlated with the Gemmatimonadetes biomass. Overall, inoculating Cd-tolerant bacteria improved the microbial activity, diversity, and abundance, and changed the microbial community composition, facilitating the remediation of Cd-contaminated soil by L. perenne.

Study on the solidification/stabilization of cadmium-contaminated soil by red mud-assisted blast furnace slag under excitation conditions

In the context of contaminated soils and industrial solid waste utilizations, a low-carbon curing agent (RAS) was synthesized in this study using red mud (RM), blast furnace slag (GGBS), calcium carbide residue (CCR), and phosphogypsum (PG) for solidification/stabilization (S/S) of cadmium (Cd)-contaminated soils. The effects of Cd contents, RAS dosages, and curing times on the strength and leaching properties of the solidified/stabilized soil were investigated in this study. In addition, the main mechanisms governing the RAS-based S/S of the Cd-contaminated soil were revealed using an improved four-step extraction method (BCR), mercury intrusion porosimetry (MIP), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The results showed that the RAS binder significantly enhanced the compressive strength and Cd chemical stability of the Cd-contaminated soil, thereby reducing Cd2+ leaching amounts and soil porosity. The soil strength and Cd2+ leaching amounts from the solidified/stabilized soil met their corresponding standards after 14 days of curing. The main products of the solidified/stabilized soil consisted of Cd precipitates, ettringite (AFt), and calcium silicate hydrate (C–S–H). Their contents were related to the initial soil Cd content, RAS dosage, and curing time. The Cd precipitate, C–S–H, and AFt products can not only fill inter-particle voids of the soil but also exhibit physical encapsulation, surface complexation, co-precipitation, electrostatic adsorption, and ion exchange effects on Cd. The results of this study can provide a novel approach for treating and utilizing solid wastes and an environmentally friendly, economical, and efficient curing agent for the remediation of Cd-contaminated soils.

Effects of Nano-zero-valent Iron and Earthworms on Soil Physicochemical Properties and Microecology in Cadmium-Contaminated Soils

The capacity of nano-zero-valent iron (nZVI) and soil animals to remediate heavy metal–contaminated soil has been widely studied. However, the synergistic effect of soil animals and nZVI has not been thoroughly investigated. Here, we studied the combined effect of earthworms and nZVI on soil physicochemical properties and microecology during remediation of cadmium (Cd)–contaminated soil. The results showed that although amendment with nZVI reduced earthworm survival and biomass, the combination of nZVI and earthworms was effective at reducing the available Cd (ACd) content of soil and improving its quality. ACd most effectively reduced by 75.3% in the presence of earthworms under the 0.25% nZVI combination. Meanwhile, the combined action of earthworms and nZVI significantly improved soil properties and increased the diversity of soil microorganisms. In the earthworm-free system, nZVI reduced ACd by increasing soil pH and the abundance of Stenotrophobacter in Cd-contaminated soil, in addition to the co-precipitation and adsorption reported in previous studies. Correlation analysis revealed that the combination of nZVI and earthworms synergistically decreased ACd by decreasing soil OM and increasing the relative abundance of Opitutus and Gemmatta. Overall, our study indicates that the combination of nano-zero-valent iron and earthworms is a potential system for in situ remediation of Cd-contaminated soils and provides a deep understanding of the mechanisms involved in remediation.

The effects of titanium dioxide nanoparticles on cadmium bioaccumulation in ramie and its application in remediation of cadmium-contaminated soil

Cadmium (Cd) is a toxic heavy metal contaminant in agricultural soils. Phytoremediation using hyperaccumulator plants is a promising remediation strategy. This study investigated the effects of TiO2 NPs on Cd uptake and accumulation in the hyperaccumulator ramie (Boehmeria nivea L.) grown in Cd-spiked soil. The aim was to evaluate the potential application of TiO2 NPs to enhance the phytoextraction efficiency of ramie for removing Cd from contaminated soils. Ramie was cultivated in soil spiked with 5 mg/kg Cd, with or without 500 mg/kg TiO2 NPs. The results showed TiO2 NPs significantly increased Cd concentrations in roots, stems, and leaves of ramie by 35%, 75%, and 278% respectively, compared to control plants. Cd levels reached 146 mg/kg in roots and 102 mg/kg in leaves with TiO2 NPs. The bioconcentration factor rose from 21.6 to 29.2 and translocation factor from 0.3 to 0.7 with nanoparticles. This indicates TiO2 NPs increased Cd bioavailability in soil and translocation to shoots. The higher Cd accumulation, especially in leaves, demonstrates the potential of TiO2 NPs to improve ramie's phytoextraction capacity. With TiO2 NP treatment, soil Cd levels decreased by an estimated 20–30% after 8 weeks of ramie cultivation, indicating enhanced phytoextraction. This study provides evidence that the application of TiO2 NPs can enhance the efficiency of phytoremediation using hyperaccumulator plants like ramie for remediation of Cd-contaminated soils.

Integration with carbon capture technology enables a positive carbon balance for sustainable rice paddy remediation with calcium‑silicon composites

In situ stabilization technologies based on lime-derived materials are extensively used for remediating Cd-contaminated paddy soils. However, the environmental impacts and carbon budget associated with these technologies throughout the paddy soil remediation life cycle are gaining increasing attention. Herein, through paddy field trials, two representative lime-derived materials, quicklime and calcium–silicon composite (Ca/Si), are evaluated for their remediation effectiveness and environmental sustainability in the remediation of Cd-contaminated soils. The results demonstrate that both quicklime and Ca/Si can reduce Cd bioavailability and enable the safe use of rice grain. Nevertheless, the life cycle assessment score of the quicklime case is 4.4 times that of the Ca/Si case, indicating that the quicklime case has a greater negative impact on the environment. Furthermore, the net ecosystem carbon budget analysis reveals that both lime-derived materials exhibit outward carbon emissions throughout their life cycle, in which the carbon emission of the quicklime case (−20.2 t CO2-eq/ha) is 20 times that of the Ca/Si case (−1 t CO2-eq/ha). Moreover, the implementation of carbon capture technology results in the Ca/Si case achieving a positive carbon budget and contributing to a carbon neutrality plan. Conversely, the quicklime case falls short, affording only a 24.8 % reduction in carbon emissions. Overall, this study provides valuable insights into the environmental sustainability of different lime-derived materials for paddy soil remediation and carbon mitigation.

Screening of Cadmium-Resistant Microbes to Improve the Tolerance of Sorghum bicolor (L.) Moench Against Cadmium

To improve the cadmium (Cd) resistance and the remediation ability of Sorghum bicolor (L.) Moench, fourteen Cd-resistant bacteria were screened from cadmium-contaminated soil, together with two strains preserved in the laboratory. It was found that 3 strains (ZR451, ZR452, and ZJSH1) significantly promoted the growth of Cd-stressed S. bicolor in hydroponics and mitigated Cd toxicity to plants, and SR8, ZRK1, and ZR211 promoted sorghum growth lightly. Further studies indicated that strains SR8, ZR211, and ZJSH1 were Cd-resistant and acid-resistant strains. Strains ZR211and ZR121 significantly produced two hormones (SA and GA), ZJSH1 significantly produced IAA and SA, and strains SR8, ZR451 and ZR452 produced one hormone. Strains SR8, ZR451, ZR452, and ZJSH1 produced siderophores. In addition, strain ZJSH1fixed nitrogen and produced ACC deaminase, while ZR451 and ZJSH1 solubilized phosphorus Correlation analysis showed that the Cd resistance of the strains was significantly and positively correlated with their IAA and GA production. The screening of the three cadmium resistant strains ZJSH1 (Sphingomonas paucimobilis), ZR451 (Bacillus cereus) and ZR452 (Bacillus cereus) provided bacterial resources for the efficient remediation of Cd-contaminated soils by bacterial - S. bicolor combination.

Exploring cadmium stress responses in sisal roots: Insights from biochemical and transcriptome analysis.

Sisal is a leaf fiber crop with a high integrated value and a wide range of uses in the application of soil remediation of heavy metal contamination. This study provides a preliminary understanding of how sisal responds to Cd stress and presents a theoretical basis for exploring the potential of sisal in the remediation of Cd-contaminated soils. In this work, the activities of the antioxidant enzymes (SOD, POD, and CAT) of sisal were measured by hydroponics with the addition of CdCl2·2.5H2O and different concentrations of Cd stress. Whole transcriptome sequencing (RNA-Seq) analysis was performed with lllumina sequencing technology, and qRT-PCR was conducted to verify the differential genes. The results obtained were as follows: (1) Short-term low concentration of Cd stress (20 mg/kg) had a transient promotion effect on the growth of sisal roots, but Cd showed a significant inhibitory effect on the growth of sisal roots over time. (2) Under different concentrations of Cd stress, the Cd content in sisal root was greater than that in sisal leaf, and Cd accumulated mainly in sisal roots. (3) With the increase of Cd stress concentration, the antioxidant enzyme catalase activity increased, peroxidase activity showed a decreasing trend, and superoxide dismutase showed a trend of increasing and then decreasing. (4) Transcriptome sequencing analysis detected 123 differentially expressed genes (DEGs), among which 85 genes were up-regulated and 38 genes were down-regulated. The DEGs were mainly concentrated in flavonoid biosynthesis and glutathione metabolism, and both processes had some regulatory effects on the Cd tolerance characteristics of sisal. This study elucidated the physiological, biochemical and transcriptomic responses of sisal under cadmium stress, and provided a theoretical basis for the ecological restoration function of sisal.

Enhanced Cd activation by Coprinus comatus endophyte Bacillus thuringiensis and the molecular mechanism

Fungal endophytes not only tolerate and activate Cd in soil but also promote host growth, yet its Cd activation capacity and mechanism remain unrevealed. Our previous study isolated a robust endophyte Bacillus thuringiensis L1 from Coprinus comatus fruiting body with splendid Cd resistance and activation abilities under laboratory conditions. In this study, those peculiarities were investigated in the actual soil environment. L1 could significantly increase the soil bioavailable Cd content and effectively compensate for alkali-hydro nitrogen losses and microbial inhibition caused by Cd. Furthermore, L1 inoculation improved the soil's bacterial community structure and increased the relative abundance of Cd-resistant bacteria, such as Actinobacteria, Chloroflexi, Acidobacter, and Firmicutes, closely associated with the soil enzyme activity shift. The genome sequencing analysis revealed the presence of genes related to growth promotion, resistance to Cd stress, and Cd activation, which were significantly up-regulated under Cd stress. Notably, L1 mainly activates Cd in soil by secreting citric acid, succinic acid, siderophore, and soluble phosphorus substances to chelate with Cd or dissolve bounded Cd. Meanwhile, the metal-responsive transcription repressor (CadC) and the Cd-translocating protein P-type ATPase (CadA) can help the L1 to suppress the toxicity of Cd. Those results help to unveil the possible mechanism of L1 in Cd-contaminated soil remediation, providing a clear strategy for Cd bio-extraction from soil.

A WRKY transcription factor, PyWRKY71, increased the activities of antioxidant enzymes and promoted the accumulation of cadmium in poplar

Cadmium (Cd) pollution poses significant threats to the ecological environment and human health. Currently, phytoremediation is recognized as an environmentally friendly approach for mitigating Cd pollution, with increasing attention on the utilization of transgenic plants in Cd-contaminated soil remediation. In this study, we isolated and cloned PyWRKY71 from Populus yunnanensis and conducted a pot experiment to validate its enhanced functionality in conferring Cd tolerance to woody plants (poplar). During the experiment, the increase in plant height of the OE-87 line (overexpression poplar) was 1.46 times than that of the wild type (WT). Moreover, PyWRKY71 significantly promoted the accumulation of Cd in poplar, especially in the roots, where the Cd content in the OE-45 and OE-87 lines was 1.42 times than that in the WT. The chlorophyll content of transgenic poplar leaves was higher than that of the WT, reflecting a protective mechanism of PyWRKY71. Additionally, the activities of other antioxidants, including POD, SOD, CAT, and MDA, were elevated in transgenic poplars, bolstering their tolerance to Cd stress. In summary, PyWRKY71 exhibits substantial potential in regulating plant tolerance to Cd stress. This study not only provides a solid scientific foundation but also introduces a novel modified poplar variety for the remediation of Cd pollution.

Keystone taxa of phoD-harboring bacteria mediate alkaline phosphatase activity during biochar remediation of Cd-contaminated soil

Phosphorus (P)-modified biochar can efficiently remediate cadmium (Cd)-contaminated soil. However, the mechanisms of responses of alkaline phosphatase (ALP) and phoD-harboring microorganisms, which are notably sensitive to Cd and P, are not clear during the remediation process. In this study, apple (Malus domestica) tree branches were co-pyrolyzed with tripotassium phosphate (K3PO4) to prepare P-modified biochar, which was used to remediate Cd-soil contaminated soil collected near a mine site. The effect of P-modified biochar on the composition of the phoD-harboring microbial community and its mechanism of interacting with ALP were analyzed. The results showed that the application of P-modified biochar to Cd-contaminated soil promoted the co-precipitation of Cd and phosphate and reduced the content of bioavailable Cd by 69.77 %. P-modified biochar improved the complexity and stability of the soil phoD-harboring microbial community. Furthermore, this study clarified that ALP activity was not completely regulated by the abundance of phoD, but Priestia and Massilia that contain phoD genes dominated the activity of ALP in rhizosphere and bulk soils, respectively. It is notable that bioavailable Cd significantly stimulated Priestia, Massilia, and ALP activity. These findings provide a theoretical basis for the application of P-modified biochar to the remediation of soil contaminated with Cd with respect to P functional microorganisms.

The responses of soil Cd fractions to disinfestation regimes associated with microbial communities

While reductive soil disinfestation (RSD)-related practices have been shown to mediate soil cadmium (Cd) fraction to a certain extent, the underlying mechanisms remain unclear. Here, a pot experiment was conducted to investigate the effects of various reductive soil disinfestation regimes on Cd fraction and its driving mechanisms underlying them. Five Cd fractions, soil physicochemical properties as well as microbial communities were simultaneously measured. Results revealed that, relative to the control treatment, all RSD-related regimes contributed to decrease exchangeable Cd fraction (EX-Cd) by transforming it to unexchangeable Cd fractions (RES-Cd CB/OX-Cd fractions) (P < 0.05). RSD with Hermetia illucens L. feces treatment (abbr.: HI treatment) had the greatest reduction rate (9.7 %), which higher than that of other treatment (3.5 % and 2.6 %), this largely attributed to more functional genera in association with Cd fixation and Fe (III) reduction enriched. In addition, soil disinfestation regimes altered soil microbial community composition and structure, which was a critical factor responsible for the changes of soil Cd fraction. Correlation analysis showed that the changes of Cd fraction were closely related to biotic and abiotic factors. Both pH and soil organic material were main abiotic factors, while microbial groups, including Bacteroidetes, Hydrogenedentes (Hydrogenispora), Ascomycota, Acidobacteria and Verrucucomicrobia were key biotic factors for Cd conversion and immobilization. The validation experiment in four vegetables further confirmed that RSD-related regimes were indeed favorable for decreasing soil availability and plant uptake of Cd by improving soil pH, and HI treatment showed optimal remediation and utilization potential to Cd-contaminated soils. Together, the results provide a theoretical basis and reference for the RSD-related disinfestation regimes in remediation of Cd-contaminated soils, and highlighted the significant potential of Hermetia illucens L. feces as a novel addition in RSD technology for reducing available Cd from soils.

Synergistic passivation performance of cadmium pollution by biochar combined with sulfate reducing bacteria

The use of sulfate-reducing bacteria (SRB) for the remediation of Cd-contaminated soil is an attractive option. However, there are various factors that limit the activity of free SRB in soil, which hinders the rapid reduction of sulfate. The immobilized SRB technology has been proposed as a possible solution to overcome this barrier. This study aimed to isolate an Enterobacter sp. strain (SRB15-3-2) with high resistance to Cd2+ from a tailing. Wheat, maize, and rice straws were selected to prepare biochar for inoculating the screened bacteria. The results showed that wheat straw biochar pyrolyzed at 700 °C (WS700) had the highest performance in carrying SRB for Cd2+ immobilization. Furthermore, the WS700 was found to promote SRB15-3-2 for offering S2− and functional groups (C-S, C=O, C=C, C-C=O, and C-O-C, etc.) during the immobilization process. The immobilized SRB with WS700 (ISRBWS700) agglomerated and reacted with Cd2+ to form metal precipitations, predominantly CdS and CdCO3. Which lead to a significant decrease of exchangeable-Cd in contaminated soil (with initial Cd concentrations of 1, 5, and 20 mg/kg) by 18.5%–31.6% after applying the ISRBWS700, indicating that the indigenous soil microbes were been protected from Cd toxicity. Additionally, ISRBWS700 exhibited a synergistic effect in enhancing SRB15-3-2 propagation and the activities of saccharase, urease, and acid phosphatase, compared to the separate treatment of SRB15-3-2 and WS700. Overall, ISRBWS700 prepared in this study represented an accessible way to resolve Cd-contaminated soil, which provided new theoretical insights into eco-friendly technologies for Cd-polluted soil remediation both in development and sustainable aspects.

NPs-Ca promotes Cd accumulation and enhances Cd tolerance of rapeseed shoots by affecting Cd transfer and Cd fixation in pectin

The use of rapeseed (Brassica napus) as a hyperaccumulator plant has shown great promise for the remediation of cadmium (Cd) contaminated soils. Nanosized materials (NPs) have been shown to mitigate heavy metal toxicity in plants, but it is unknown how l-aspartate nano-calcium (NPs-Ca) affects Cd uptake, transport, and tolerance in rapeseed. A soil pot experiment was conducted with two treatments: a control treatment (CK) with 2.16 g CaCl2 and NPs-Ca treatment with 6.00 g NPs-Ca, to evaluate the effects and mechanisms of NPs-Ca on Cd tolerance in rapeseed. Compared to CaCl2, NPs-Ca promoted Cd transportation from roots to shoots by up-regulating the expression of Cd transport genes (ABCC12, HMA8, NRAM6, ZIP6, CAX4, PCR2, and HIP6). Therefore, NPs-Ca increased Cd accumulation in rapeseed shoots by 39.4%. Interestingly, NPs-Ca also enhanced Cd tolerance in the shoots, resulting in lower hydrogen peroxide (H2O2) accumulation and proline content, as well as higher antioxidant enzyme activities (POD, CAT). Moreover, NPs-Ca reduced the activity of pectin-degrading enzymes (polygalacturonase: PG, β-galactosidase: β-GAL), promoted the activity of pectin methyl esterase (PME), and changed transcription levels of related genes (PME, PMEI, PG, PGIP, and β-GAL). NPs-Ca treatment also significantly increased the Cd content in cell walls by 59.8%, that is, more Cd was immobilized in cell walls, and less Cd entered organelles in shoots of NPs-Ca treatment due to increased pectin content and degree of pectin demethylation. Overall, NPs-Ca increased Cd accumulation in rapeseed shoots by promoting Cd transport from roots to shoots. And meantime, NPs-Ca enhanced Cd tolerance of shoots by inhibiting pectin degradation, promoting pectin demethylation and increasing Cd fixation in pectin. These findings suggest that NPs-Ca can improve the potential of rapeseed as a hyperaccumulator for the remediation of Cd-contaminated soil and the protection of the environment. Furthermore, the study provides a theoretical basis for the application of NPs-Ca in the phytoremediation of Cd-contaminated soils with hyperaccumulating plants.