Combined biochar and wheat-derived endophytic bacteria reduces cadmium uptake in wheat grains in a metal-polluted soil.

In this study, two wheat-derived cadmium (Cd)-immobilizing endophytic Pseudomonas paralactis M14 and Priestia megaterium R27 were evaluated for their effects on wheat tissue Cd uptake under hydroponic conditions. Then, the impacts of the biochar (BC), M14+R27 (MR), and BC+MR treatments on wheat Cd uptake and the mechanisms involved were investigated at the jointing, heading, and mature stages of wheat plants under field-plot conditions. A hydroponic experiment showed that the MR treatment significantly decreased the above-ground tissue Cd content compared with the M14 or R27 treatment. The BC+MR treatment reduced the grain Cd content by 51.5%-67.7% and Cd translocation factor at the mature stage of wheat plants and increased the organic matter-bound Cd content by 31%-75% in the rhizosphere soils compared with the BC or MR treatment. Compared with the BC or MR treatment, the relative abundances of the biomarkers associated with Gemmatimonas, Altererythrobacter, Gammaproteobacteria, Xanthomonadaceae, Phenylobacterium, and Nocardioides in the BC+MR-treated rhizosphere microbiome decreased and negatively correlated with the organic matter-bound Cd contents. In the BC+MR-treated root interior microbiome, the relative abundance of the biomarker belonging to Exiguobacterium increased and negatively correlated with the Cd translocation factor, while the relative abundance of the biomarker belonging to Pseudonocardiaceae decreased and positively correlated with the Cd translocation factor. Our findings suggested that the BC+MR treatment reduced Cd availability and Cd transfer through affecting the abundances of these specific biomarkers in the rhizosphere soil and root interior microbiomes, leading to decreased wheat grain Cd uptake in the contaminated soil.

Effect of silicon spraying on rice photosynthesis and antioxidant defense system on cadmium accumulation.

Cadmium (Cd) pollution is a serious threat to food safety and human health. Minimizing Cd uptake and enhancing Cd tolerance in plants are vital to improve crop yield and reduce hazardous effects to humans. In this study, we designed three Cd concentration stress treatments (Cd1: 0.20 mg·kg-1, Cd2: 0.60 mg·kg-1, and Cd3: 1.60 mg·kg-1) and two foliar silicon (Si) treatments (CK: no spraying of any material, and Si: foliar Si spraying) to conduct pot experiments on soil Cd stress. The results showed that spraying Si on the leaves reduced the Cd content in brown rice by 4.79-42.14%. Si application increased net photosynthetic rate (Pn) by 1.77-4.08%, stomatal conductance (Gs) by 5.27-23.43%, transpiration rate (Tr) by 2.99-20.50% and intercellular carbon dioxide (CO2) concentration (Ci) by 6.55-8.84%. Foliar spraying of Si significantly increased the activities of superoxide dismutase (SOD) and peroxidase (POD) in rice leaves by 9.84-14.09% and 4.69-53.09%, respectively, and reduced the content of malondialdehyde (MDA) by 7.83-48.72%. In summary, foliar Si spraying protects the photosynthesis and antioxidant system of rice canopy leaves, and is an effective method to reduce the Cd content in brown rice.

[Immobilization of Heavy Metals by Phosphorus-solubilizing Bacteria and Inhibition of Cd and Pb Uptake by Wheat].

Phosphorus-solubilizing microorganisms convert insoluble phosphorus in the soil into phosphorus that can be absorbed by plants. Soluble phosphate combines with heavy metals to form precipitation, reducing the content of available heavy metals, thereby reducing the absorption of heavy metals by crops, which plays an important role in the remediation of heavy metal-contaminated soil. The effects of the immobilization of Cd and Pb and the release of PO43- by the phosphorus-solubilizing bacterium Klebsiella sp. M2 were studied through solution culture experiments. In addition, the effects of strain M2 on wheat uptake of Cd and Pb and its microbiological mechanism were also explored through pot experiments. The results showed that strain M2 reduced the concentrations of Cd and Pb and increased the concentration of PO43- in the solution through cell wall adsorption and induced phosphate precipitation. Pot experiments showed that compared to those in the CK group and inactivated strain M2 group, inoculation with live strain M2 significantly increased （123%-293%） the contents of Ca2-P and Ca8-P in rhizosphere soil, decreased the content of DTPA-Cd （34.48%） and DTPA-Pb （36.72%） in wheat rhizosphere soil, and thus hindered the accumulation of Cd and Pb in wheat grains. Moreover, high-throughput sequencing results showed that strain M2 significantly increased the diversity of wheat rhizosphere bacterial communities； increased the relative abundance of Proteobacteria, Gemmatimonadetes, and Bacteroidota in wheat rhizosphere soil； and increased the proportion of heavy metal-immobilizing and phosphorus-promoting bacteria in wheat rhizosphere soil （mainly Sphingomonas, Nocardioides, Bacillus, Gemmatimonas, and Enterobacter）. These bacterial genera played an important role in immobilizing heavy metals and preventing wheat from absorbing heavy metals. These results provide bacterial resources and theoretical basis for the bioremediation of heavy metal-contaminated farmland.

Inhibition of microbially mediated total organic carbon decomposition in different types of cadmium contaminated soils with wheat straw addition.

Wheat straw returning is a common agronomic measure in the farmland. Understanding organic carbon transformation is of great significance for carbon budget under the premise of widespread distribution of cadmium (Cd) contaminated soils. An incubation experiment was conducted to assess the influence of Cd contamination on the decomposition and accumulation of total organic carbon (TOC) as well as the composition and abundance of bacterial communities in eight soil types with wheat straw addition. The results showed that inhibition of Cd contamination on microbially mediated organic carbon decomposition was affected by soil types. The lower cumulative C mineralization and higher TOC content could be observed in the acidic soils relative to that in the alkaline soils. The content of Cd in soil exhibits different effects on the inhibition in decomposition of TOC. The high dosage level of Cd had stronger inhibitory impact due to its high toxicity. The decomposition of TOC was restricted by a reduction in soil bacterial abundance and weakening of bacterial activities. Redundancy analysis (RDA) indicated that Proteobacteria and Gemmatimonadetes were abundant in alkaline Cd-contaminated soils with wheat straw addition, while Bacteroidetes dominated cumulative C mineralization in acidic Cd-contamination soils. Moreover, the abundance of predicted functional bacteria indicated that high-dose Cd-contamination and acid environment all inhibited the decomposition of TOC. The present study suggested that pH played an important role on carbon dynamics in the Cd-contaminated soils with wheat straw addition.

Bioaccumulation of Cadmium in Muscle and Liver Tissues of Juvenile Yellowfin Tuna (Thunnus albacares) from the Indian Ocean.

The present study evaluated the cadmium (Cd) levels and temporal variation of Cd in dark muscle, white muscle, and liver of juvenile Thunnus albacares. 72 individuals (Standard length: 50-67 cm; weight: 0.8-2.5 kg) were collected from Indian Oceanic water around Sri Lanka during the period between April 2021 to May 2022. Total Cd levels were analyzed using an Inductively Coupled Plasma Mass Spectrophotometer. The mean Cd levels (mean ± SD mg kg-1 dry weight) in different tissues varied with significantly higher levels in the liver (13.62 ± 0.98, p < 0.05), compared to dark muscle (0.52 ± 0.05), and white muscle (0.42 ± 0.04). Cd levels in liver tissues were positively correlated (p < 0.05) with the fish weight. The Cd levels reported in dark muscles, white muscles, and liver tissues were significantly higher (p < 0.05) during 2nd inter-monsoon than in the other monsoonal regimes and exceeded the maximum permissible level (0.1 mg kg-1 wet weight) set by the European Union (EU). However, the measured Cd levels in white and dark muscles were below the maximum permissible level (0.2 mg kg-1 wet weight) set by FAO/WHO. The Cd levels in all the liver tissues were above the levels set by the EU and FAO/WHO. Accordingly, people should avoid the consumption of liver tissues of T. albacares from the Indian Ocean. A human with a body weight of 60 kg can consume white muscles up to 4.667 kg per week without exceeding the Provisional Tolerable Weekly Intake.

Effect of Genotype on Cadmium and Trace Element Accumulation in Wheat from Weakly Alkaline Cadmium-contaminated Soil.

Cadmium (Cd) contamination of farmland soils leads to Cd accumulation in crops and reduced micronutrient uptake, posing grave risks to food safety. Herein, we investigated the enrichment and transportation patterns of Cd and trace elements in different parts of six wheat genotypes grown in weakly alkaline Cd-contaminated soils via pot experiments. The results revealed that the wheat grain variety with high Cd accumulation (Ningmai13) demonstrated a 1.94-fold increase compared to the variety with low accumulation (Yanong0428). The transfer factor of Cd from wheat straw to grain ranged from 0.319 to 0.761, while the transfer factor of Cd from root to straw ranged from 0.167 to 0.461. Furthermore, the concentrations of other metals in wheat grains followed the order of Zn > Mn > Fe > Cu. There was a significant positive correlation between Cd and Mn in grains, indicating a potential synergistic effect. Overall, this study provides valuable insights into the regulation of micronutrient intake to modulate Cd uptake in wheat.

The effects of monoculture and intercropping on photosynthesis performance correlated with growth of garlic and perennial ryegrass response to different heavy metals.

BACKGROUND: The potential of phytoremediation using garlic monoculture (MC) and intercropping (IC) system with perennial ryegrass to enhance the uptake of cadmium (Cd), chromium (Cr), and lead (Pb) were investigated. RESULTS: Positive correlations were found between MC and IC systems, with varying biomass. Production of perennial ryegrass was affected differently depending on the type of toxic metal present in the soil. Root growth inhibition was more affected than shoot growth inhibition. The total biomass of shoot and root in IC was higher than MC, increasing approximately 3.7 and 2.9 fold compared to MC, attributed to advantages in root IC crop systems. Photosystem II efficiency showed less sensitivity to metal toxicity compared to the control, with a decrease between 10.07-12.03%. Among gas exchange parameters, only Cr significantly affected physiological responses by reducing transpiration by 69.24%, likely due to leaf chlorosis and necrosis. CONCLUSION: This study exhibited the potential of garlic MC and IC with perennial ryegrass in phytoremediation. Although the different metals affect plant growth differently, IC showed advantages over MC in term biomass production.

Unlocking Cd(II) biosorption potential of Candida tropicalis XTA 1874 for sustainable wastewater treatment.

Cd(II) is a potentially toxic heavy metal having carcinogenic activity. It is becoming widespread in the soil and groundwater by various natural and anthropological activities. This is inviting its immediate removal. The present study is aimed at developing a Cd(II) resistant strain isolated from contaminated water body and testing its potency in biological remediation of Cd(II) from aqueous environment. The developed resistant strain was characterized by SEM, FESEM, TEM, EDAX, FT-IR, Raman Spectral, XRD and XPS analysis. The results depict considerable morphological changes had taken place on the cell surface and interaction of Cd(II) with the surface exposed functional groups along with intracellular accumulation. Molecular contribution of critical cell wall component has been evaluated. The developed resistant strain had undergone Cd(II) biosorption study by employing adsorption isotherms and kinetic modeling. Langmuir model best fitted the Cd(II) biosorption data compared to the Freundlich one. Cd(II) biosorption by the strain followed a pseudo second order kinetics. The physical parameters affecting biosorption were also optimized by employing response surface methodology using central composite design. The results depict remarkable removal capacity 75.682 ± 0.002% of Cd(II) by the developed resistant strain from contaminated aqueous medium using 500 ppm of Cd(II). Quantitatively, biosorption for Cd(II) by the newly developed resistant strain has been increased significantly (p < 0.0001) from 4.36 ppm (non-resistant strain) to 378.41 ppm (resistant strain). It has also shown quite effective desorption capacity 87.527 ± 0.023% at the first desorption cycle and can be reused effectively as a successful Cd(II) desorbent up to five cycles. The results suggest that the strain has considerable withstanding capacity of Cd(II) stress and can be employed effectively in the Cd(II) bioremediation from wastewater.

Multifunctional Roles of Zinc in Cadmium Transport in Soil-Rice Systems: Novel Insights from Stable Isotope Fractionation and Gene Expression.

The effect of Zn on Cd accumulation in rice varies under flooding and drainage conditions, and the underlying mechanism during uptake and transport from the soil to grains remains unclear. Isotope fractionation and gene expression were investigated using pot experiments under distinct water regimes and with Zn addition to gain a deeper understanding of the molecular effects of Zn on Cd uptake and transport in rice. The higher OsHMA2 expression but constitutively lower expression of zinc-regulated, iron-regulated transporter-like protein (ZIP) family genes in roots under the drainage regime than the flooding regime caused the enrichment of nonheavy Zn isotopes in the shoots relative to roots but minimally affected Cd isotopic fractionation. Drainage regime seem to exert a striking effect on the root-to-shoot translocation of Zn rather than Cd, and increased Zn transport via OsHMA2. The changes in expression patterns in response to Zn addition were similar to those observed upon switching from the flooding to drainage regime, except for OsNRAMP1 and OsNRAMP5. However, soil solution-to-rice plants and root-to-shoot fractionation toward light Zn isotopes with Zn addition (Δ66Znrice plant-soil solution = -0.49 to -0.40‰, Δ66Znshoot-root = -0.36 to -0.27‰) indicated that Zn transport occurred via nonspecific uptake pathways and OsHMA2, respectively. Accordingly, the less pronounced and minimally varied Cd isotope fractionation suggested that OsNRAMP5 and OsHMA2 are crucial for Cd uptake and root-to-shoot transport, respectively, facilitating Cd accumulation in grains. This study demonstrated that a high Zn supply promotes Cd uptake and root-to-shoot transport in rice by sharing distinct pathways, and by utilizing a non-Zn-sensitive pathway with a high affinity for Cd.

Populus euphratica CPK21 Interacts with NF-YC3 to Enhance Cadmium Tolerance in Arabidopsis.

The toxic metal cadmium (Cd) poses a serious threat to plant growth and human health. Populus euphratica calcium-dependent protein kinase 21 (CPK21) has previously been shown to attenuate Cd toxicity by reducing Cd accumulation, enhancing antioxidant defense and improving water balance in transgenic Arabidopsis. Here, we confirmed a protein-protein interaction between PeCPK21 and Arabidopsis nuclear transcription factor YC3 (AtNF-YC3) by yeast two-hybrid and bimolecular fluorescence complementation assays. AtNF-YC3 was induced by Cd and strongly expressed in PeCPK21-overexpressed plants. Overexpression of AtNF-YC3 in Arabidopsis reduced the Cd inhibition of root length, fresh weight and membrane stability under Cd stress conditions (100 µM, 7 d), suggesting that AtNF-YC3 appears to contribute to the improvement of Cd stress tolerance. AtNF-YC3 improved Cd tolerance by limiting Cd uptake and accumulation, activating antioxidant enzymes and reducing hydrogen peroxide (H2O2) production under Cd stress. We conclude that PeCPK21 interacts with AtNF-YC3 to limit Cd accumulation and enhance the reactive oxygen species (ROS) scavenging system and thereby positively regulate plant adaptation to Cd environments. This study highlights the interaction between PeCPK21 and AtNF-YC3 under Cd stress conditions, which can be utilized to improve Cd tolerance in higher plants.

Preparation of porous biochar from fusarium wilt-infected banana straw for remediation of cadmium pollution in water bodies.

The problem of cadmium pollution and its control is becoming increasingly severe issue in the world. Banana straw is an abundant bio raw material, but its burning or discarding in field not only causes pollution but also spreads fusarium wilt. The objective of this paper is to utilize biochar derived from the wilt-infected banana straw for remediation of Cd(II) pollution while to eliminate the pathogen. The activity of wilt pathogen in biochar was determined by PDA petri dish test. The Cd(II) adsorption of the biochar was determined by batch adsorption experiments. The effects of KOH concentration (0.25, 0.5 and 0.75 M) on the physicochemical characteristics of the biochar were also observed by BET, SEM, FTIR, XRD and XPS. Results showed that pristine banana straw biochar (PBBC) did not harbor any pathogen. The specific surface area (SSA) and Cd(II) adsorption capacity of 0.75 M KOH modified banana straw biochar (MBBC0.75M) were increased by 247.2% and 46.1% compared to that of PBBC, respectively. Cd(II) adsorption by MBBC0.75M was suitable to be described by the pseudo-second-order kinetic model and Freundlich isotherm. After Cd(II) adsorption, the CdCO3 were confirmed by XRD and observed through SEM. The weakness and shift of oxygen-containing functional groups in MBBC0.75M after Cd(II) adsorption implied that those groups were complexed with Cd(II). The results showed that pyrolysis could not only eliminate banana fusarium wilt, but also prepare porous biochar with the wilt-infected banana straw. The porous biochar possessed the potential to adsorb Cd(II) pollutants.

[Effects of Four Amendments on Cadmium Bioavailability and Enzyme Activity in Purple Soil].

In this study, the effects of four types of amendments on effective Cd and Cd content in different parts of prickly ash soil and soil enzyme activity were studied, which provided scientific basis for acidification improvement of purple soil and heavy metal pollution control. A field experiment was conducted. Six treatments were set up:no fertilizer (CK), only chemical fertilizer (F), lime + chemical fertilizer (SF), organic fertilizer + chemical fertilizer (OM), biochar + chemical fertilizer (BF), and vinasse biomass ash + chemical fertilizer (JZ). Soil pH; available Cd (DTPA-Cd); Cd content in branches, leaves, shells, and seeds of Zanthoxylum; as well as the activities of catalase (S-CAT), acid phosphatase (S-ACP), and urease (S-UE) in different treatments were studied, and their relationships were clarified. The results showed following:① The two treatments of vinasse biomass ash + chemical fertilizer and lime + chemical fertilizer significantly increased soil pH (P < 0.05) to 3.39 and 2.25 units higher than that in the control, respectively. Compared with that in the control treatment, the content of available Cd in soil under vinasse biomass ash + chemical fertilizer and lime + chemical fertilizer treatment decreased by 28.91 % and 20.90 %, respectively. ② The contents of Cd in leaves, shells, and seeds of Zanthoxylum were decreased by 31.33 %, 30.24 %, and 34.01 %, respectively. The Cd enrichment ability of different parts of Zanthoxylum was different, with the specific performances being leaves > branches > seeds > shells. Compared with that of the control, the enrichment coefficient of each part of Zanthoxylum treated with vinasse biomass ash + chemical fertilizer decreased significantly(P < 0.05)by 27.54 %-40.0 %. ③ The changes in catalase and urease activities in soil treated with amendments were similar. Compared with those in the control group, the above two enzyme activities were significantly increased by 191.26 % and 199.50 %, respectively, whereas the acid phosphatase activities were decreased by 16.45 %. Correlation analysis showed that soil available Cd content was significantly negatively correlated with soil pH value(P < 0.01), S-CAT and S-UE enzyme activities were significantly positively correlated with soil pH(P < 0.01), and the soil available Cd content was significantly negatively correlated (P < 0.01); the S-ACP enzyme showed the complete opposite trends. The application of lime and vinasse biomass ash to acidic purple soil had the most significant effect on neutralizing soil acidity. It was an effective measure to improve acidic purple soil and prevent heavy metal pollution by reducing the effective Cd content in soil and improving the soil environment while inhibiting the absorption and transfer of Cd in various parts of Zanthoxylum.

[Effect of Exogenous Chitosan on Physiological Properties, Antioxidant Activity, and Cadmium Uptake of Wheat (Triticum aestivum L.) Seedlings Under Cadmium Stress].

This research aimed to clarify the effects of exogenously applied chitosan on the physiological characteristics, antioxidant activities, and Cd accumulation of wheat (Triticum aestivum L.) seedlings under cadmium (Cd) stress and to identify the key indicators based on the partial least squares model. The wheat variety studied was Bainong207 (BN207), and Cd-stress was achieved by growing seedlings in a hydroponic culture experiment with 10 and 25 µmol·L-1 Cd2+ added to the culture solution. It was found that both Cd-stress at 10 and 25 µmol·L-1 significantly inhibited the chlorophyll content, photosynthesis, and biomass accumulation of wheat seedlings. Seedling roots became shorter and thicker, and the lateral roots decreased under Cd-stress. The Cd-stress also increased H2O2 and MDA accumulation and the degree of cell membrane lipid peroxidation and affected the activities of antioxidant enzymes such as superoxide dismutase (SOD) and peroxidase (POD). Under Cd stress, exogenous chitosan decreased the Cd content in the aboveground and underground parts of wheat by 13.22 %-21.63 % and 7.92 %-28.32 % and reduced Cd accumulation in the aboveground and underground parts by 5.37 %-6.71 % and 1.91 %-4.09 %, respectively. Whereas exogenous chitosan application significantly reduced the content of H2O2 in roots and aboveground parts of wheat by 38.21 %-47.46 % and 45.81 %-55.73 % and MDA content by 37.65 %-48.12 % and 29.87 %-32.51 %, it increased the activities of SOD and POD in roots by 2.78 %-5.61 % and 13.81 %-18.33 %, respectively. In summary, exogenous chitosan can improve the photosynthetic characteristics and antioxidant enzyme activities of wheat seedlings under Cd stress, reduce the content and accumulation of Cd in the root and aboveground parts of wheat, and alleviate the damage of lipid peroxidation to the cell membrane. All of these results provide the basal data for the application of exogenous chitosan to alleviate Cd toxicity to wheat seedlings.

Metabolic regulation mechanism of melatonin for reducing cadmium accumulation and improving quality in rice.

Melatonin acts as a potential regulator of cadmium (Cd) tolerance in rice. However, its practical value in rice production remains unclear. To validate the hypothesis that melatonin affects Cd accumulation and rice quality, a series of experiments were conducted. The results showed that exogenous melatonin application was associated with reduced Cd accumulation (23-43%) in brown rice. Fourier transform infrared spectroscopy (FTIR) analysis showed that exogenous melatonin affected the rice protein secondary structure and starch short-range structure. Metabolomics based on LC-MS/MS revealed that exogenous melatonin altered the brown rice metabolic profile, decreased fatty acid metabolite content, but increased amino acid metabolite, citric acid, melatonin biosynthetic metabolite, and plant hormone contents. These findings indicate that exogenous melatonin can effectively reduced Cd accumulation and improve rice quality through metabolic network regulation, serving as an effective treatment for rice cultivated in Cd-contaminated soil.

Conjoint analysis of physio-biochemical, transcriptomic, and metabolomic reveals the response characteristics of solanum nigrum L. to cadmium stress.

Cadmium (Cd) is a nonessential element in plants and has adverse effects on the growth and development of plants. However, the molecular mechanisms of Cd phytotoxicity, tolerance and accumulation in hyperaccumulators Solanum nigrum L. has not been well understood. Here, physiology, transcriptome, and metabolome analyses were conducted to investigate the influence on the S. nigrum under 0, 25, 50, 75 and 100 µM Cd concentrations for 7 days. Pot experiments demonstrated that compared with the control, Cd treatment significantly inhibited the biomass, promoted the Cd accumulation and translocation, and disturbed the balance of mineral nutrient metabolism in S. nigrum, particularly at 100 µM Cd level. Moreover, the photosynthetic pigments contents were severely decreased, while the content of total protein, proline, malondialdehyde (MDA), H2O2, and antioxidant enzyme activities generally increased first and then slightly declined with increasing Cd concentrations, in both leaves and roots. Furthermore, combined with the previous transcriptomic data, numerous crucial coding-genes related to mineral nutrients and Cd ion transport, and the antioxidant enzymes biosynthesis were identified, and their expression pattern was regulated under different Cd stress. Simultaneously, metabolomic analyses revealed that Cd treatment significantly changed the expression level of many metabolites related to amino acid, lipid, carbohydrate, and nucleotide metabolism. Metabolic pathway analysis also showed that S. nigrum roots activated some differentially expressed metabolites (DEMs) involved in energy metabolism, which may enhance the energy supply for detoxification. Importantly, central common metabolism pathways of DEGs and DEMs, including the "TCA cycle", "glutathione metabolic pathway" and "glyoxylate and dicarboxylate metabolism" were screened using conjoint transcriptomics and metabolomics analysis. Our results provide some novel evidences on the physiological and molecular mechanisms of Cd tolerance in hyperaccumulator S. nigrum plants.

Influences of earthworm activity and mucus on Cd phytoremediation based on harvesting different leaf types of tall fescue (Festuca arundinacea).

To explore cost-effective and efficient phytoremediation strategies, this study investigated the distinct roles of earthworm activity and mucus in enhancing Cd phytoextraction from soils contaminated by Festuca arundinacea, focusing on the comparative advantages of selective leaf harvesting versus traditional whole-plant harvesting methods. Our study employed a horticultural trial to explore how earthworm activity and mucus affect Festuca arundinacea' s Cd phytoremediation in soils using control, earthworm, and mucus treatments to examine their respective effects on plant growth and Cd distribution. Earthworm activity increased the dry weight of leaves by 13.5% and significantly increased the dry weights of declining and senescent leaves, surpassing that of the control by more than 40%. Earthworm mucus had a similar, albeit less pronounced, effect on plant growth than earthworm activity. This study not only validated the significant role of earthworm activity in enhancing Cd phytoextraction by Festuca arundinacea, with earthworm activity leading to over 85% of Cd being allocated to senescent tissues that comprise only approximately 20% of the plant biomass, but also highlighted a sustainable and cost-effective approach to phytoremediation by emphasizing selective leaf harvesting supported by earthworm activity. By demonstrating that earthworm mucus alone can redistribute Cd with less efficiency compared to live earthworms, our findings offer practical insights into optimizing phytoremediation strategies and underscore the need for further research into the synergistic effects of biological agents in soil remediation processes.

Ecotoxicity of Cadmium along the Soil-Cotton Plant-Cotton Bollworm System: Biotransfer, Trophic Accumulation, Plant Growth, Induction of Insect Detoxification Enzymes, and Immunocompetence.

Cadmium (Cd) is a hazardous element that may jeopardize environmental safety and human health through biotransfer and trophic accumulation. Here, we tested Cd toxicity on cotton plants, cotton bollworms, and their responses. Results demonstrated that Cd accumulated in plant roots, aerial parts, insect larvae, pupae, and frass in a dose-dependent pattern. The ∼9.35 mg kg-1 of Cd in plant aerial parts, ∼3.68 in larvae, ∼6.43 in pupae, and high transfer coefficient (∼5.59) indicate significant mobility. The ∼19.61 mg kg-1 of Cd in larvae frass suggests an effective detoxification strategy, while BAFcotton (∼1.14) and BAFworm (∼0.54) indicated low bioaccumulation. Cadmium exposure resulted in compromised plant growth and yield as well as alterations in photosynthetic pigment contents, antioxidant enzyme activities, and certain life history traits of cotton bollworms. Furthermore, carboxylesterase activity and encapsulation rates of insect larvae decreased with increasing Cd concentrations, whereas acetylcholinesterase, phenol oxidase, glutathione S-transferase, and multifunctional oxidase exhibited hormesis responses.

Prediction of the bioaccessibility and accumulation of cadmium in the soil-rice-human system based on optimized DGT and BCR coupled models.

Cadmium, as a typical heavy metal, has the potential to induce soil pollution and threaten human health through the soil-plant-human pathway. The conventional evaluation method based on the total content in soil cannot accurately represent the content migrated from the food chain to plants and the human body. Previous studies focused on the process of plant enrichment of heavy metals in soil, and very few studies directly predicted human exposure or risk through the labile state of Cd in soil. Hence, a relatively accurate and convenient prediction model of Cd release and translocation in the soil-rice-human system was developed. This model utilizes available Cd and soil parameters to predict the bioavailability of Cd in soil, as well as the in vitro bioaccessibility of Cd in cooked rice. The bioavailability of Cd was determined by the Diffusive Gradients in Thin-films technology and BCR sequential extraction procedure, offering in-situ quantification, which presents a significant advantage over traditional monitoring methods and aligns closely with the actual uptake of heavy metals by plants. The experimental results show that the prediction model based on the concentration of heavy metal forms measured by BCR sequential extraction procedure and diffusive gradients in thin-films technique can accurately predict the Cd uptake in rice grains, gastric and gastrointestinal phase (R2=0.712, 0.600 and 0.629). This model accurately predicts Cd bioavailability and bioaccessibility across the soil-rice-human pathway, informing actual human Cd intake, offering scientific support for developing more effective risk assessment methods.

Effects of Cd(II) on nitrogen removal by a heterotrophic nitrification aerobic denitrification bacterium Pseudomonas sp. XF-4.

Simultaneous heterotrophic nitrification and aerobic denitrification (SND) is gaining tremendous attention due to its high efficiency and low cost in water treatment. However, SND on an industrial scale is still immature since effects of coexisting pollutants, for example, heavy metals, on nitrogen removal remains largely unresolved. In this study, a HNAD bacterium (Pseudomonas sp. XF-4) was isolated. It could almost completely remove ammonium and nitrate at pH 5-9 and temperature 20 ℃-35 ℃ within 10 h, and also showed excellently simultaneous nitrification and denitrification efficiency under the coexistence of any two of inorganic nitrogen sources with no intermediate accumulation. XF-4 could rapidly grow again after ammonium vanish when nitrite or nitrate existed. There was no significant effects on nitrification and denitrification when Cd(II) was lower than 10 mg/L, and 95 % of Cd(II) was removed by XF-4. However, electron carrier and electron transport system activity was inhibited, especially at high concentration of Cd(II). Overall, this study reported a novel strain capable of simultaneous nitrification and denitrification coupled with Cd(II) removal efficiently. The results provided new insights into treatment of groundwater or wastewater contaminated by heavy metals and nitrogen.

Effect of exogenous γ-aminobutyric acid on physiological property, antioxidant activity, and cadmium uptake of quinoa seedlings under cadmium stress.

Increasing cadmium (Cd) pollution has negative effects on quinoa growth and production. Gamma-aminobutyric acid (GABA) confers plants with stress resistance to heavy metals; however, the mechanism remains unclear. We explored the effects of exogenous GABA on the physiological characteristics, antioxidant capacity, and Cd accumulation of quinoa seedlings under Cd stress using hydroponic experiments. Partial least-squares regression was used to identify key physical and chemical indices of seedlings affecting Cd accumulation. Compared with those of the CK group, exposure to 10 and 25 µmol·L-1 Cd significantly reduced the photosynthetic pigment contents, photosynthesis, and biomass accumulation of quinoa seedlings; resulted in shorter and thicker roots; decreased the length of the lateral roots; decreased the activities of superoxide dismutase (SOD) and peroxide (POD); and increased H2O2 and malondialdehyde (MDA) contents. Exogenous GABA reduced the Cd content in the stem/leaves and roots of quinoa seedlings under Cd stress by 13.22-21.63% and 7.92-28.32%, decreased Cd accumulation by 5.37-6.71% and 1.91-4.09%, decreased the H2O2 content by 38.21-47.46% and 45.81-55.73%, and decreased the MDA content by 37.65-48.12% and 29.87-32.51%, respectively. GABA addition increased the SOD and POD activities in the roots by 2.78-5.61% and 13.81-18.33%, respectively, under Cd stress. Thus, exogenous GABA can reduce the content and accumulation of Cd in quinoa seedlings by improving the photosynthetic characteristics and antioxidant enzyme activity and reducing the degree of lipid peroxidation in the cell membrane to alleviate the toxic effect of Cd stress on seedling growth.