Cd Accumulation Research Articles

Enhanced phytoremediation of cadmium-contaminated soil using chelating agents and plant growth regulators: effect and mechanism.

The heavy metal cadmium (Cd) is a major threat to food safety and human health. Phytoremediation is the most widely used remediation technology, and how to improve the remediation efficiency of phytoremediation has become a key issue. In this study, we constructed an intensive phytoremediation technology for remediation of Cd-contaminated soil with biodegradable chelating agent and plant growth regulator combined with maize and investigated the mechanism of this technology. The results showed that the best remediation effect was achieved in the treatment with 10-6 mol l-1 gibberellic acid (GA3) and 6 mmol kg-1 aspartate diethoxysuccinic acid (AES) combined with maize. In this treatment, the total biomass and extraction efficiency of maize were 3.6 and 8.67 times higher than those of the control, respectively, and the antioxidant enzyme activities of maize were also increased. The soil was enriched with dominant bacterial genera that promote plant growth and metabolism and tolerance to heavy metal stress, which in turn promoted maize growth and Cd accumulation. Structural equation modelling results indicated a large effect of plant Cd concentration and plant antioxidant enzyme activity on plant Cd extraction. The enhanced phytoremediation technology showed good potential for safe use of Cd-contaminated soil.

Pretreatment with aqueous Moringa oleifera Lam. leaf extract prevents cadmium-induced hepatotoxicity by improving cellular antioxidant machinery and reducing cadmium accumulation

Cadmium (Cd) is a highly harmful pollutant that poses a serious threat to human health. The liver is the primary organ for Cd accumulation, and Cd-induced hepatotoxicity has been shown to be strongly correlated with an oxidative imbalance in hepatocytes. Our previous studies in the eukaryotic model organism Saccharomyces cerevisiae revealed that not only co-treatment but also pretreatment with aqueous Moringa oleifera Lam. leaf extract (AMOLE) effectively mitigated Cd toxicity by reducing intracellular Cd accumulation and Cd-mediated oxidative stress. In this study, we therefore investigated the preventive effect of AMOLE against Cd toxicity in human HepG2 hepatocytes. The results showed that, similar to the case of the yeast model, pretreatment with AMOLE prior to Cd exposure also significantly inhibited Cd-induced oxidative stress in HepG2 cells. Untargeted LC-MS/MS-based metabolomic analysis of AMOLE revealed that its major phytochemical constituents were organic acids, particularly phenolic acids and carboxylic acids. Additionally, DPPH-HPTLC fingerprints suggested that quercetin and other flavonoids possibly contribute to the antioxidant activities of AMOLE. Based on our findings, it appears that pretreatment with AMOLE prevented Cd-induced hepatotoxicity via three possible mechanisms: i) direct elimination of free radicals by AMOLE antioxidant compounds; ii) upregulation of antioxidant defensive machinery (GPx1, and HO-1) via Nrf2 signaling cascade to improve cellular antioxidant capacity; and iii) reduction of intracellular Cd accumulation, probably by suppressing Cd uptake. These data strongly suggest the high potential of AMOLE for clinical utility in the prevention of Cd toxicity.

Long-term adaptation of water hyacinth to low cadmium involves antioxidant enzyme and metallothionein transcriptional regulation

Cadmium (Cd) is one of the main heavy metal pollutants in environment. Water hyacinth (Eichhornia crassipes) is an effective phytoremediation plant for mitigating Cd stress, though the concentration threshold for its long-term survival remains unclear. Our results indicate that 4 mg L−1 Cd may be the maximum threshold for long-term cultivation of water hyacinth, as it significantly inhibits root growth and photosynthesis. The activity of superoxide dismutase increased under low concentration Cd treatment (0.5 and 1.0 mg L−1), potentially contributing to the reactive oxygen species (ROS) homeostasis in water hyacinth. Additionally, we identified the Cd-induced metallothionein gene MT1, whose heterologous expression in yeast enhanced Cd tolerance despite higher Cd accumulation. The upregulation of MT1 may enhance the detoxification capacity of water hyacinth under Cd stress. Our findings establish the Cd range for long-term cultivation of water hyacinth and elucidated the mechanism of its tolerance to moderate Cd stress.

Aged polylactic acid microplastics with ultraviolet irradiation alleviated the toxic effect of Cd on pakchoi (Brassica chinensis L.) in hydroponics

Biodegradable microplastics (BMPs) and cadmium (Cd) present substantial risks to agricultural systems, primarily affecting plants. Most current studies have focused on the ecological effects of virgin BMPs. However, the effects of ultraviolet (UV)-aged BMPs and their interactions with cadmium (Cd) on pakchoi remain largely unknown. Therefore, this study addressed this gap by aging polylactic acid (PLA) microplastics (MPs) through UV irradiation and conducting an indoor hydroponic experiment. The research systematically examined the individual and combined impacts of Cd, virgin, and UV-aged BMPs on pakchoi (Brassica chinensis L.), focusing on plant growth, photosynthesis, antioxidant systems, and Cd accumulation. The results showed that after 21 days of UV irradiation (UPLA MPs), UPLA MPs with a fractured surface had a more significant impact on pakchoi than untreated PLA MPs. Cd alone inhibited pakchoi growth, development, and photosynthesis, while PLA/UPLA MPs alone promoted these processes. Under the combination of Cd and PLA/UPLA MPs, UPLA MPs could effectively alleviate the toxic effect of Cd on pakchoi. Besides, Cd coexisted with PLA/UPLA MPs, and with the increase of Cd concentration, UPLA MPs(41.22 %, 66.80 %, 45.57 %) decreased the Cd content of pakchoi more significantly than PLA MPs(37.87 %, 55.91 %, 26.35 %). Meanwhile, the results of Partial least squares structural equation models (PLS-SEM) further showed that UPLA MPs could effectively reduce the accumulation of Cd in plants. Therefore, the results of this study can provide a new perspective and reference for the ecological risk evaluation of Cd and BMPs pollution in agricultural soils.

Investigation of Cd and Pb enrichment capacities of Erigeron sumatrensis across three polluted regions: Insights into soil parameters and microbial communities

Erigeron sumatrensis is a vigorously growing invasive plant in mining areas and has been the subject of research for its potential in the phytoremediation of heavy metals. In this study, the bioconcentration factor (BCF) and translocation factor (TF) of E. sumatrensis were assessed to evaluate its phytoaccumulation potential for cadmium (Cd) and lead (Pb) across three distinct zinc mining regions with different degrees of contamination, including Huayuan (HY), Yueyang (YY), and Liuyang (LY) areas. The region of HY is identified as having the most severe Cd contamination, while the most pronounced Pb pollution characterizes the LY area. The findings indicate that E. sumatrensis demonstrated a stronger ability to enrich Cd and Pb in less contaminated areas. To elucidate the underlying mechanisms, high-throughput sequencing of 16S rRNA and internal transcribed spacer (ITS) regions was employed to analyze the rhizosphere bacterial and fungal communities across the three areas. The results revealed significant variations in the microbial community structure, function, and composition, suggesting a complex interplay between the plant and its associated microorganisms. Correlation analysis identified several soil properties, including soil pH, total nitrogen (TN), available nitrogen (AN), organic matter (OM), and available phosphorus (AP), as pivotal factors that may influence the heavy metal enrichment capabilities of the plant. Notably, some microorganisms (e.g., Burkholderia, Brevundimonas, Paraglomus, and Trichoderma) and enzymes (e.g., P-type ATPases, citrate synthase, catalase) of microorganisms were found to be potentially involved in facilitating the accumulation of Cd and Pb by E. sumatrensis. This research contributes to understanding how invasive alien plants can be utilized to remedy contaminated environments. It highlights the importance of modulating critical soil factors to enhance the phytoremediation potential of E. sumatrensis, which could aid in developing strategies to manage invasive plants and mitigate heavy metal pollution in ecosystems.

Genomic and transcriptomic analyses reveal insights into cadmium resistance mechanisms of Cupriavidus nantongensis strain E324

The cadmium-resistant Cupriavidus sp. strain E324 has been previously shown to have a high potential for use in cadmium (Cd) remediation, due to its high capacity for cadmium bioaccumulation. According to the comparative genomic analysis, the strain E324 was most closely related to C. nantongensis X1T, indicating that the strain E324 should be re-identified as C. nantongensis. To unravel the Cd tolerance mechanisms of C. nantongensis strain E324, the transcriptional response of this strain to acute Cd exposure was assessed using RNA-seq-based transcriptome analysis, followed by validation through qRT-PCR. The results showed that the upregulated Differentially Expressed Genes (DEGs) were significantly enriched in categories related to metal binding and transport, phosphate transport, and oxidative stress response. Consistently, we observed significant increases in both the cell wall and intracellular contents of certain essential metals (Cu, Fe, Mn, and Zn) upon Cd exposure. Among these, only the Zn pretreatment resulting in high Zn accumulation in the cell walls could enhance bacterial growth under Cd stress conditions through its role in inhibiting Cd accumulation. Additionally, the promotion of catalase activity and glutathione metabolism upon Cd exposure to cope with Cd-induced oxidative stress was demonstrated. Meanwhile, the upregulation of phosphate transport-related genes upon Cd treatment seems to be the bacterial response to Cd-induced phosphate depletion. Altogether, our findings suggest that these adaptive responses are critical mechanisms contributing to increased Cd tolerance in C. nantongensis strain E324 via the enhancement of metal-chelating and antioxidant capacities of the cells.

IAA is more effective than EDTA in enhancing phytoremediation potential for cadmium and copper contaminated soils

Enhanced phytoremediation offers a rapid and eco-friendly approach for cleaning agricultural soil contaminated with copper and cadmium which pose a direct threat to food scarcity and security. The current study aimed to compare the effectiveness of the two commonly used additives, IAA and EDTA, for the remediation of copper (Cu) and cadmium (Cd) contaminated soils using sunflower and maize. The plants were cultivated in pots under controlled conditions with four sets of treatments: control (0), Cu50/Cd50, Cu50/Cd50 + EDTA, and Cu50/Cd50 + IAA. The results showed that Cu50/Cd50 mg/kg drastically compromised the phytoremediation potential of both plants, as evident by reduced shoot and root length, and lower biomass. However, the augmentation of Cu50/Cd50 with EDTA or IAA improved the tested parameters. In sunflower, EDTA enhanced the accumulation of Cu and Cd by 58% and 21%, respectively, and improved plant biomass by 41%, compared to control treatment. However, IAA exhibited higher accumulation of Cu and Cd by 64% and 25%, respectively, and enhanced plant biomass by 43%. In case of maize, IAA was superior to EDTA which enhanced the accumulation of Cu and Cd by 87% and 32% respectively, and increased the plant biomass by 57%, compared to control treatment. Our findings demonstrate that foliar IAA is more effective than EDTA in enhancing the phytoremediation potential of sunflower and maize for Cu and Cd.

Mechanisms of N-doped microporous biochar decreased Cd transition in rhizosphere soils and its impact on soil bacterial community composition

Soil cadmium (Cd) contamination has garnered considerable attention. This study employed batch sorption experiments and rhizobox experiments to examine the impact of nitrogen-doped microporous biochar (NBB) on the temporal and spatial distribution of Cd in the rhizosphere of rice plants, with the aim of elucidating the underlying mechanisms. The results indicated that the adsorption of Cd(II) onto NBB was predominantly governed by chemical reactions. When applied to soil, the NBB significantly hindered the migration of Cd from the bulk soil to the rhizosphere. Additionally, the application of NBB decreased the redox potential (Eh) in the rhizosphere soil and increased the relative abundance of Anaeromyxobacteraceae, Geobacteraceae, Desulfurisporaceae, and Syntrophomonadaceae, which could facilitate the reduction of soil Cd availability. Furthermore, the NBB2 treatment encouraged the formation of iron plaque on the root surface, thereby limiting the uptake of Cd from the soil into the root system. Moreover, the N-doped microporous biochar treatment resulted in lower Cd levels in the stele of root, an effect that was associated with increased sulfur (S) content in the stele and epidermis, suggesting a potential role for S in Cd sequestration. Ultimately, the application of N-doped microporous biochar resulted in diminished Cd accumulation in the rice tissues.

The MYC2 and MYB43 transcription factors cooperate to repress HMA2 and HMA4 expression, altering cadmium tolerance in Arabidopsis thaliana

Cadmium (Cd) represents a hazardous heavy metal, prevalent in agricultural soil due to industrial and agricultural expansion. Its propensity for being absorbed by edible plants, even at minimal concentrations, and subsequently transferred along the food chain poses significant risks to human health. Accordingly, it is imperative to investigate novel genes and mechanisms that govern Cd tolerance and detoxification in plants. Here, we discovered that the transcription factor MYC2 directly binds to the promoters of HMA2 and HMA4 to repress their expression, thereby altering the distribution of Cd in plant tissues and negatively regulating Cd stress tolerance. Additionally, molecular, biochemical, and genetic analyses revealed that MYC2 interacts and cooperates with MYB43 to negatively regulate the expression of HMA2 and HMA4 and Cd stress tolerance. Notably, under Cd stress conditions, MYC2 undergoes degradation, thereby alleviating its inhibitory effect on HMA2 and HMA4 expression and plant tolerance to Cd stress. Thus, our study highlights the dynamic regulatory role of MYC2, in concert with MYB43, in regulating the expression of HMA2 and HMA4 under both normal and Cd stress conditions. These findings present MYC2 as a promising target for directed breeding efforts aimed at mitigating Cd accumulation in edible plant roots.

In-situ remediation of cadmium contamination in paddy fields: from rhizosphere soil to rice kernel.

Cadmium (Cd) has become an important heavy metal pollutant because of its strong migration and high toxicity. The industrial production process aggravated the Cd pollution in rice fields. Human exposure to Cd through rice can cause kidney damage, emphysema, and various cardiovascular and metabolic diseases, posing a grave threat to health. As modern technology develops, the Cd accumulation model in rice and in-situ remediation of Cd pollution in cornfields have been extensively studied and applied, so it is necessary to sort out and summarize them systematically. Therefore, this paper reviewed the primary in-situ methods for addressing heavy metal contamination in rice paddies, including chemical remediation (inorganic-organic fertilizer remediation, nanomaterials, and composite remediation), biological remediation (phytoremediation and microbial remediation), and crop management remediation technologies.The factors that affect Cd transformation in soil and Cd migration in crops, the advantages and disadvantages of remediation techniques, remediation mechanisms, and the long-term stability of remediation were discussed. The shortcomings and future research directions of in situ remediation strategies for heavily polluted paddy fields and genetic improvement strategies for low-cadmium rice varieties were critically proposed. To sum up, this review aims to enhance understanding and serve as a reference for the appropriate selection and advancement of remediation technologies for rice fields contaminated with heavy metals.

Alleviation of cadmium uptake in rice (Oryza sativa L.) by iron plaque on the root surface generated by Providencia manganoxydans via Fe(II) oxidation.

Iron plaque is believed to be effective in reducing the accumulation of heavy metals in rice. In this work, a known soil-derived Mn(II)-oxidizing bacterium, LLDRA6, which represents the type strain of Providencia manganoxydans, was employed to investigate the feasibility of decreasing cadmium (Cd) accumulation in rice by promoting the formation of iron plaque on the root surface. Firstly, the Fe(II) oxidation ability of LLDRA6 was evaluated using various techniques including Fourier Transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, phenanthroline photometry, and FeS gel-stabilized gradient assays. Subsequently, the formation of iron plaque on the root surface by LLDRA6 was investigated under hydroponic and pot conditions. Finally, Cd concentrations were examined in rice with and without iron plaque through pot and paddy-field tests. The results showed that LLDRA6 played an efficient role in the formation of iron plaque on seedling roots under hydroponic conditions, generating 44.87 and 36.72g kg- 1 of iron plaque on the roots of Huazhan and TP309, respectively. In pot experiments, LLDRA6 produced iron plaque exclusively in the presence of Fe(II). Otherwise, it solely generated biofilm on the root surface. Together with Fe(II), LLDRA6 effectively reduced the concentrations of Cd in Huazhan roots, straws and grains by 25%, 46% and 44%, respectively. This combination also demonstrated a significant decrease in the Cd concentrations of TP309 roots, straws and grains by 20%, 52% and 44%, respectively. The data from the Cd translocation factor indicate that obstruction of Cd translocation by iron plaque predominantly occurred during the root-to-straw stage. In paddy-field tests, the Cd concentrations of grains harvested from the combination treatment of LLDRA6 and Fe(II) exhibited a decline ranging from 40 to 53%, which fell below the maximum acceptable value for Cd in rice grains (0.2mg kg- 1) as per the China national standard for food security (GB2762-2017). Meanwhile, the relevant phenotypic traits regarding the yield were not adversely affected. These findings have demonstrated that LLDRA6 can impede the uptake of Cd by rice in Cd-contaminated soils through the formation of iron plaque on roots, thus providing a promising safe Cd-barrier for rice production.

Significant alleviation of cadmium toxicity in Thalassiosira weissflogii through the combined effect of high silicon and zinc supplementation

Cadmium (Cd), a prevalent pollutant in near-shore seawater ecosystems, poses a significant threat to marine biota. Zinc (Zn) and Cd can have interchangeable physiological effects in marine plankton, and both can influence the synthesis of siliceous walls. Consequently, the concentrations of zinc and silicon may jointly impact the toxicity of Cd. This study endeavors to elucidate the combined effect of silicon (Si) and zinc (Zn) on the growth and physiological responses of the marine diatom species Thalassiosira weissflogii when subjected to Cd-induced stress conditions (190.7 μg L−1). Our results reveal statistically improvements (p<0.05) in biomass production, reductions (p<0.05) in superoxide dismutase (SOD) activity and extracellular secretion in T. weissflogii when high concentrations of Si (172 µmol L−1) and Zn (18.3 nmol L−1) were applied simultaneously. Additionally, examination of Cd bioconcentration factors (BCF) derived from Cd uptake kinetics and intracellular Cd content measurements underscores the ability of elevated Si and Zn concentrations to reduce intracellular Cd accumulation (p<0.05). The ability of Si and Zn to mitigate Cd toxicity was further evidenced by increased cellular biosilica content and maintenance of cell morphology, suggesting a protective role in preserving structural integrity and growth. Our findings underscore the synergistic benefits of Si and Zn in enhancing the resilience of T. weissflogii to Cd stress, providing valuable insights into the potential use of nutrient amendments as a strategy for mitigating heavy metal contamination in marine environments.

Cadmium contamination in sediments from a mangrove wetland: Insights from lead isotopes

Cadmium (Cd) pollution has gained significant attention in mangrove sediments due to its high toxicity and mobility. However, the sources of Cd and the factors influencing its accumulation in these sediments have remained elusive. In this study, we utilized lead (Pb) isotopic signatures for the first time to assess Cd contamination in mangrove sediments from the northern region of the Beibu Gulf. A strong correlation was observed between Cd and Pb concentrations in the mangrove sediments, suggesting a shared source that can be estimated using Pb isotopic signatures. By employing a Bayesian mixing model, we determined that 70.1 ± 8.2 % of Cd originated from natural sources, while 12.9 ± 4.9 %, 9.8 ± 3.7 %, and 7.1 ± 3.4 % were attributed to agricultural activities, non-ferrous metal smelting, and coal combustion, respectively. Our study clearly suggests that natural Cd could also dominate the high Cd content. Agricultural activities were the most important anthropogenic Cd sources, and the increased anthropogenic Cd accumulation in mangrove sediment was related to organic matter. This study introduces a novel approach for assessing Cd contamination in mangrove sediment, providing useful insights into Cd pollution in coastal wetlands.

Role of SbNRT1.1B in cadmium accumulation is attributed to nitrate uptake and glutathione-dependent phytochelatins biosynthesis

Phytoremediation of cadmium (Cd)-polluted soil by using sweet sorghum displays a tremendous potential as it is a fast-growing, high biomass and Cd tolerant energy plant. Previous study has demonstrated SbNRT1.1B expression change is in accordance with enhanced Cd accumulation by external nitrate supply in sweet sorghum. Nevertheless, underlying mechanism of SbNRT1.1B response to Cd stress is still elusive. SbNRT1.1B exhibited a positive response to Cd stress in sweet sorghum. Overexpressing SbNRT1.1B increased primary root length, shoot fresh weight, nitrate and chlorophyll concentrations compared with Col-0 under Cd stress, while complementary SbNRT1.1B rescued these decreased values in mutant chl1–5. Cd concentrations in overexpressing SbNRT1.1B, complementary SbNRT1.1B and Col-0 lines were 3.2–4.1, 2.5–3.1 and 1.2–2.1 folds of that in chl1–5. Consistent with Cd concentrations, non-protein thiol (NPT), reduced glutathione (GSH) and phytochelatins (PCs) concentrations as well as the related genes expression levels showed the same trends under Cd stress. GSH biosynthesis inhibitor failed to reverse the patterns of GSH-dependent PCs concentrations changes in different lines, suggesting that SbNRT1.1B plays an upstream role in GSH-dependent PCs biosynthesis under Cd treatment. Altogether, SbNRT1.1B enhances nitrate concentrations contributing to increased chlorophyll concentrations and GSH-dependent PCs metabolites biosynthesis, thereby improving growth and Cd concentrations in plants.

Endophytic Colletotrichum fructicola KL19 and Its Derived SeNPs Mitigate Cd-Stress-Associated Damages in Spinacia oleracea L.

The application of nanotechnology in agriculture has received much attention in order to improve crop yield, quality and food safety. In the present study, a Cd-tolerant endophytic fungus Colletotrichum fructicola KL19 was first ever reported to produce SeNPs, and the production conditions were optimized using the Box-Behnken design in the Response Surface Methodology (RSM-BBD), achieving a peak yield of 1.06 mM under optimal conditions of 2.62 g/20 mL biomass, 4.56 mM Na2SeO3, and pH 6.25. Following this, the properties of the biogenic SeNPs were elucidated by using TEM, DLS, and FTIR, in which the 144.8 nm spherical-shaped SeNPs were stabilized by different functional groups with a negative zeta potential of -18.3 mV. Furthermore, strain KL19 and SeNPs (0, 5, 10, 20 and 50 mg/L) were inoculated in the root zone of small-leaf spinach (Spinacia oleracea L.) seedlings grown in the soil with 33.74 mg/kg Cd under controlled conditions for seven weeks. Impressively, compared with Cd stress alone, the strain KL19 and 5 mg/L SeNPs treatments significantly (p < 0.05) exhibited a reduction in Cd contents (0.62 and 0.50 folds) within the aboveground parts of spinach plants and promoted plants' growth by improving the leaf count (0.92 and 1.36 folds), fresh weight (2.94 and 3.46 folds), root dry weight (4.00 and 5.60 folds) and root length (0.14 and 0.51 folds), boosting total chlorophyll synthesis (0.38 and 0.45 folds), enhancing antioxidant enzymes (SOD, POD) activities, and reducing the contents of reactive oxygen species (MDA, H2O2) in small-leaf spinach under Cd stress. Overall, this study revealed that utilizing endophytic fungus C. fructicola or its derived SeNPs could mitigate reactive oxygen species generation by enhancing antioxidant enzyme activity as well as diminish the absorption and accumulation of Cd in small-leaf spinach, promoting plant growth under Cd stress.

Predicting Cd accumulation in crops and identifying nonlinear effects of multiple environmental factors based on machine learning models

The traditional prediction of the Cd content in grains (Cdg) of crops primarily relies on the multiple linear regression models based on soil Cd content (Cds) and pH, neglecting inter-factorial interactions and nonlinear causal links between external environmental factors and Cdg. In this study, a comprehensive index system of multi-type environmental factors including soil properties, geology, climate, and anthropogenic activity was constructed. The machine learning models of the tree-based ensemble, support vector regression, artificial neural network for predicting Cdg of rice and wheat based on the environmental factor indexes significantly improved the accuracy than the traditional models of linear regression based on soil properties. Among them, the tree-based ensemble models of XGboost and random forest exhibited highest accuracies for predicting Cdg of rice and wheat, with R2 in the test dataset of 0.349 and 0.546, respectively. This study found that soil properties, including Cds, pH, and clay, have greater impacts on Cdg of rice and wheat, with combined contribution rates accounting for 65.2 % and 29.7 % respectively. Since wheat sampling areas are located in central and northern China, they are more constrained by precipitation and temperature than rice sampling areas in the south. Geologic and climate factors have a greater impact on Cdg of wheat, with a combined contribution rate of 49.9 %, which is higher than the corresponding rate of 20.9 % in rice. Furthermore, the Cdg of rice and wheat did not exhibit an absolute linear relationship with Cds, and excessively high Cds can reduce the bioconcentration factor of Cd accumulation in crops. Meanwhile, other environmental factors such as temperature, precipitation, elevation have marginal effects on the increase of Cdg of crops. This study provides a novel framework to optimize traditional soil plant transfer models, as well as offer a step towards realizing high precision prediction of Cd content in crops.

Spatial distribution and factors influencing the accumulation of toxic metals in soils in mountain agroecosystems, Rio De Janeiro, Brazil.

The concentrations of toxic metals (TM) were analyzed in 498 samples of agricultural soils used for intensive vegetable cultivation in the watershed of Barracão dos Mendes, Brazil. The goal of this study was to characterize the distribution of these elements and the main natural and anthropogenic factors affecting their accumulation. In general, the average concentrations of TM were higher than the reference quality values for cultivated soils in the region, with the exception of Cr, Co, Ni and Mn, and the average concentration of Cd was ten times greater. Three sources of variation in the distribution of TM concentrations were identified: one related to topographic relief, another related to lithology, and one related to the massive use of agrochemicals. These factors contributed to TM accumulation in the soil; moreover, the transport of toxic metal-enriched clay by runoff resulted in higher concentrations of these elements in the lower parts of the slope. The long-term application of massive amounts of fertilizers and pesticides resulted in the accumulation of Cr, Cu, Zn, Ni, Pb and Cd in the vegetable cultivation soils and promoted the enrichment of macronutrients, mainly P and K. Moreover, the spatial distribution of TM in the agricultural soils of this mountain agroecosystem was affected by intensive vegetable cultivation, which altered the natural TM distribution dynamics determined by variations in topographic relief and lithology. In intensive cultivation areas, the TM distribution was also influenced by soil management practices such as tillage along the slope direction and massive mineral and organic fertilization.

Transcriptome analysis of potassium-mediated cadmium accumulation in sweet sorghum

Cadmium (Cd) pollution in the soil is a serious environmental issue worldwide. Phytoextraction of Cd-polluted soil is a cost-effective, sustainable and environmentally-friendly strategy. Agricultural fertilizer management is beneficial for promoting the Cd phytoremediation efficiency. Potassium (K) is the nutrient required in the largest amount cation by plants. Sweet sorghum exhibits a substantial phytoremediation potential of Cd-polluted soil. Clarifying the mechanism of K-mediated Cd accumulation in sweet sorghum is imperative. Sweet sorghum plants were grown hydroponically with an extra K supply in the presence or absence of Cd treatment. An extra K application significantly increased plant growth under non-Cd addition, while K lost the profitable effect under Cd stress. K supplementation remarkably enhanced Cd concentrations and Cd accumulation in shoots and roots of sweet sorghum. Transcriptome analysis demonstrated that zinc ion transport, cysteine and methionine metabolism, flavonoid biosynthesis and phenylpropanoid biosynthesis pathways might contribute to the increased Cd accumulation as affected by an extra K supply. Furthermore, SbZIP9, SbSTP8, SbYS1, SbMAG and SbFOMT-like were targeted as they closely correlated with both plant growth and Cd stress in sweet sorghum. SbFOMT-like showed an independent pathway, while SbZIP9, SbSTP8, SbYS1 and SbMAG displayed positive correlations mutually. Notably, SbZIP9 and SbFOMT-like were highly expressed when compared with other target genes. Taken together, SbZIP9 and SbFOMT-like were upregulated and downregulated by an extra K supply under Cd stress, suggesting that SbZIP9 and SbFOMT-like enhances and declines Cd accumulation as regulated by K addition in sweet sorghum respectively.

Different shifts in growth-defense tradeoff for above- and belowground of Miscanthus floridulus enhance tolerance to cadmium

The growth-defense tradeoff is a central mechanism for plants to cope with environmental challenges. Soil contamination with heavy metals, especially cadmium (Cd), can strongly influence the adaptive capacity of plants by modulating both growth and defense. However, how the growth-defense tradeoff adaptive to Cd stress and its dynamic patterns are not yet known. To elucidate these patterns, we conducted an experiment with the pioneer plant Miscanthus floridulus by subjecting it to a gradient of exogenous Cd concentrations, and calculated root mean square deviation based on 12 traits to decipher the direction and intensity of the growth-defense tradeoff. We observed that growth traits such as photosynthetic rate, chlorophyll content, above- and belowground biomass, root surface area and root diameter decreased under Cd stress, while the antioxidative compounds increased. Notably, both above- and belowground parts showed a preference for growth in the absence of Cd stress (tradeoff intensity= 0.013 and 0.013, respectively, unitless). However, under the high Cd stress (40 mg/kg), the aboveground tradeoff remained towards growth (tradeoff intensity= 0.024), while the belowground tradeoff shifted towards defense (tradeoff intensity= −0.046). Under 10 and 20 mg/kg Cd stress, the shifts were uncertain towards either growth or defense for above and belowground parts, suggesting a complex above-belowground interplay. The belowground tradeoff was mainly influenced by plant Cd accumulation, soil fluorescein diacetate hydrolase (S.FDA), and soil available potassium. In contrast, the aboveground tradeoff was primarily driven by plant hydrogen peroxide (H₂O₂) accumulation, S.FDA, and soil alkaline phosphomonoesterase. Overall, Cd in soil altered physicochemical properties and Cd accumulation, which in turn had a significant impact on belowground defense mechanisms. We revealed that the shifts in growth-defense tradeoff differed between aboveground and belowground under Cd stress. Our results provided a new insight into the physiological and biochemical mechanisms underlying plant adaptation to Cd stress from the perspective of the growth-defense tradeoff.

Remediation of cadmium contaminated soil using electrokinetic-phytoremediation system with rotary switching electrodes.

Considering both electrokinetic remediation and phytoremediation have limitations, an electrokinetic phytoremediation (EP) system was constructed to obtain efficient and environmentally friendly remediation results. This study indicates that the electric field can promote the absorption of Cd by ryegrass with little impact on soil physicochemical properties under the condition of rotary switching electrodes, and the accumulation of Cd in the aboveground and underground parts of ryegrass increased by 145.2% and 93.7%, respectively. The DC electric field combined with ryegrass under rotary switching electrode mode proved to be the optimal condition for the remediation of Cd contaminated soil with a remediation efficiency of 66.7%. Moreover, the rotary switching of the electrodes alleviated the suppression of the growth of ryegrass by the DC electric field. During the EP remediation process, the electric field promoted the transformation of the residue state of Cd to the other forms, which accelerated the desorption rate of Cd from the soil and facilitated the migration of Cd into plants. In conclusion, EP is a green and efficient remediation technology for heavy metal contaminated soil with good application prospects.