Comparing the effects of calcium and magnesium ions on accumulation and translocation of cadmium in rice

Squaraine dye as a fluorescent probe for highly sensitive detection of pyrophosphate and alkaline phosphatase

We synthesized a squaraine dye (F-0) to develop a method for detecting pyrophosphate (PPi) and alkaline phosphatase (ALP) by modulating the fluorescence of F-0. The fluorescence intensity of the F-0 system was quenched upon the addition of Cu2+ ions; however, it was restored when PPi was introduced due to the formation of a complex between PPi and Cu2+. Since ALP can hydrolyze PPi, the fluorescence of the system was quenched again upon the addition of ALP. Based on these principles, we established a fluorescent probe that exhibits an "off-on-off" fluorescence response. The detection limits of this method for PPi and ALP were 103 nmol dm-3 and 0.18 U dm-3, respectively. Moreover, this method demonstrates good selectivity and specificity and can be applied to the detection of PPi in actual samples.

Integrated physiological, transcriptomic, and metabolomic investigation reveals that MgO NPs mediate the alleviation of cadmium stress in tobacco seedlings through ABA-regulated lignin synthesis

The harmful influence caused by cadmium (Cd) to agriculture is severe and enduring. Efforts to reduce the damage by Cd to crop is an important topic. In this study, we investigated the effect of MgO NPs on tobacco seedlings' growth under Cd stress and explored its mechanism. Results showed Cd inhibited seedling growth, but MgO NPs alleviated this toxicity. With MgO NPs, shoot and root fresh weight increased by 35.12 % and 45.73 %. This was mainly due to MgO NPs reducing Cd accumulation by 40 % in root and 20.48 % in shoot compared to Cd treatment. MgO NPs not only reduced Cd accumulation but redistributed it to inactive cell walls: up to 55 % in shoot and 22 % in root (compared to 47 % and 22 % in Cd treatment). The primary mechanism was the change in cell wall's main ingredient: lignin. MgO NPs increased lignin content by 50.62 % compared to Cd treatment. To further investigate the underlying molecular mechanism, multi-omics analysis was conducted. Comparing Cd + MgO NPs with Cd, 1358 DEGs (694 up, 664 down) and 160 DEMs (44 up, 116 down) were identified. Furthermore, we identified ABA-regulated phenylpropanoid pathway as the key mechanism for lignin synthesis. MgO NPs boosted ABA levels by 6.72 % compared to Cd treatment. The multi-omics analysis revealed upregulation of ABA synthesis and signal transduction, leading to increased phenylpropanoid pathway metabolites and gene expressions. Notably, POD, a key enzyme, increased by 92.05 %. It was concluded that MgO NPs represent a highly efficient alternative for enhancing plant resistance to Cd.

Tomato sprayed monocalcium phosphate had production-phytoremediation dual function with high soil Cd extraction and safer fruit production

In order to make use of the large biomass of tomato plant to fulfill the purpose of remediating-while-producing, two commercial tomato varieties, 'Baiguoqiangfeng' (BG) and 'Ouguan' (OG) were grown in Cd contaminated acidic soil to compare their performance on Cd phytoextraction, and monocalcium phosphate (Ca) was foliar applied to reduce their fruit Cd concentration. The results showed that the BG was a more Cd tolerant variety, comparing with OG, it suffered lighter tissue peroxidation and photosynthesis obstacle, owning weaker amino acid metabolism, secondary metabolism and stress signal transduction under Cd stress. The Ca application reduced its ABA level but increased the GSH, IAA, ZR and GA3 level, and enhanced its lysine degradation, tyrosine metabolism, alanine, asparagine and glutamate metabolism, plant hormone signal transduction and phenylpropanoid biosynthesis under Cd stress. With these metabolic regulations, the Ca application promoted its leaf biomass accumulation, guaranteeing the total Cd extraction amount (0.88 mg pot-1 as 0.20 mg kg -1), and reduced the fruit Cd partition, decreasing the fruit Cd concentration by 71.4% with higher yield. Meanwhile, the OG had lower Cd phytoextraction capacity than the BG, and Ca spray enhanced its cell energy generation, flavonoids biosynthesis and photosynthetic carbon fixation, but had no effect on fruit Cd concentration. The two tomato varieties had different responses to Ca application under Cd stress in their hormone signaling, energy metabolism, secondary metabolism and amino acids metabolism, which furtherly differed their Cd phytoextraction capacity and production safety. Therefore, the monocalcium phosphate spray combined 'Baiguoqiangfeng' tomato realized the dual function of production-phytoremediation, and the mechanism of plant Cd sensitivity adjustment through phenylpropanoid biosynthesis and amino acids metabolism deserved further study.

Calcium-magnesium synergy in reducing cadmium bioavailability and uptake in rice plants

The synergistic application of calcium (Ca) and magnesium (Mg) was investigated to mitigate cadmium (Cd) uptake and translocation in rice grown in Cd-contaminated soil. A pot experiment was conducted using different Ca:Mg molar ratios (Ca1:Mg2, Ca2:Mg1, and Ca1:Mg1) to evaluate their effect on Cd uptake. The results showed that the Ca1:Mg1 treatment achieved the highest reduction in grain Cd content (54.7%, p < 0.05), followed by Ca2:Mg1 (47.6%), and Ca1:Mg2 (40.7%), all below China's National Food Safety Standard (0.2 mg kg-1). Significant reductions were also observed in roots, stems, and leaves (p < 0.05). Ca1:Mg1 minimized Cd translocation by decreasing stem-to-grain transfer by 61.0% and xylem sap Cd by 50.1% (p < 0.05). It also reduced mobile Cd fractions in roots (F_E from 25% to 18%, F_Di from 44% to 37%) and increased DCB-extractable Fe (DCB-Fe) on roots, enhancing Cd immobilization. Ca:Mg treatments raised soil pH by 23.6-25.7% (p < 0.05), shifting Cd from bioavailable forms (F_EX reduced by 9.3%, F_CB by 17.8%) to more stable forms (F_Fe/Mn increased by 15.5%, F_OM by 1.9%). Strong negative correlations (p < 0.05, 0.01) between soil pH, DCB-Fe, Ca, Mg_TF, F_Fe/Mn, and grain Cd indicating their effect in reducing Cd uptake.

Foliar spraying of carbon dots reduces cadmium accumulation in rice by regulating rhizosphere immobilization, root development, and subcellular distribution

Cadmium (Cd) is a toxic heavy metal widespread in rice paddies and threatens food safety and human health. Foliar exposure represents a cost-effective, simple, and time-independent approach to enhance rice resistance and minimize Cd accumulation. Herein, foliar spraying of carbon dots (CDs) was found to significantly reduce Cd accumulation in rice roots and shoots by 31.51 % and 17.93 %, respectively. Gene expression and mineral nutrient analyses indicated that CDs exposure inhibited Cd uptake by suppressing OsNramp1 and increasing competition of Fe and Mn with Cd for OsNramp5. Besides, CDs exposure down-regulated OsHMA2 for Cd transport from roots to aerial parts and up-regulated OsHMA3 for Cd vacuole sequestration. Additionally, CDs treatment promoted rice root development by increasing root biomass, cell walls, and mechanical resistance, which helped to anchor rice plants and impede Cd uptake. Furthermore, CDs spraying increased the organic carbon content and altered the microbial communities in the rice rhizosphere by increasing root exudation. This process facilitated the binding of dissolved Cd in pore water to organic matter and iron‑manganese oxides, ultimately reducing the bioavailability of Cd. This study underscores the effectiveness and mechanism of simple foliar spraying of CDs to mitigate Cd accumulation in rice.

A holistic field experimental inquiry into cadmium's migration and translocation dynamics across the entire growth spectrum of five Japonica rice cultivars

The contamination of farmland soils with cadmium (Cd) poses a substantial threat to agricultural productivity, food security and safety, and ultimately human health. However, little research has been done on the Cd transport mechanisms in highly Cd polluted soil via field experiment. This study, from a field-scale perspective, examines the migration and transformation features of Cd throughout the growth cycle of five (C1, C2, C3, C4, H1) Japonica rice cultivars in Jiangsu Province, China. Analysis of pH, SOM, total Cd, DTPA-Cd, and microbial communities were conducted. C1 ~ C3 were classified as High Cd-accumulating rice (HC), while C4 and H1 were considered as low Cd-accumulating rice (LC) based on the Cd levels in their brown rice. Phloem was confirmed as the main pathway for Cd into rice grains in high-Cd soil. For the HC group, the Cd concentration in brown and polished rice was positively correlated with the Cd concentration in the leaves and spikes; while for the LC group, they were significantly positively correlated with the Cd concentration in both stem and spike (p < 0.05). The husks of the LC group were more effective in intercepting and sequestering Cd. It was revealed that 6 % ~ 9.09 % of the Cd content detected in the rice grains could be attributed to the internal translocation processes occurring within the plant itself, and approximately 90.91 % ~ 93.84 % of the Cd was traced back to the roots' absorption during grouting. Rice polishing decreased the Cd content from the level in the brown rice by 18 % ~ 47 %. Distinct microbial profiles separated rice rhizosphere from bulk soil, with the former favouring copiotrophs in nutrient-rich zones and the latter oligotrophs in lean conditions. This study delivers crucial data support from a field perspective for a deeper understanding and control of Cd migration and transformation processes in highly Cd-contaminated soil.

Milk vetch returning combined with lime materials alleviates soil cadmium contamination and improves rice quality in soil-rice system

Milk vetch (Astragalus sinicus L.) returning and lime materials is employed as an effective strategy for remediating cadmium (Cd)-contaminated paddy fields. However, the combined effects of them on alleviating Cd pollution and the underlying mechanisms remain poorly explored. Therefore, this study investigated the impact of these combined treatments on soil properties, iron oxides, iron plaque, mineral elements, and amino acids through a field experiment. The following treatments were employed: lime (LM), limestone (LS), milk vetch (MV), MV + LM (MVLM), and MV + LS (MVLS), and a control (CK) group with no materials. Results demonstrated that treatments significantly decreased soil available Cd by 19.40-32.55 %, 10.20-39.58 %, and 25.36-40.66 % at tillering, filling, and maturing stages compared to CK, respectively. Moreover, exchangeable Cd was transformed into more stable fractions. Compared with individual treatments, MVLM and MVLS treatments further decreased available Cd and exchangeable Cd. Overall, Cd in brown rice was reduced by 18.97-77.39 % compared with CK. And the Cd in iron plaque decreased by 14.12-31.14 %, 24.65-61.60 %, 2.6-38.28 % across three stages. Furthermore, soil pH, dissolved organic carbon, and cation exchange capacity increased, along with 0.22-62.09 % and 0.57-10.66 % increases in free and amorphous iron oxide contents at all stages, respectively. Compared with lime alone, the integration of MV returning facilitated increased formation of Fed, Feo and enhanced the antagonistic effect among grain Ca with Cd; Additionally, it increased AAs in brown rice, improving rice quality and potentially reducing Cd transport. Mantel tests and Partial least squares path modeling revealed a significant positive correlation between Cd in IP and rice Cd uptake and a significant negative correlation between available Cd, Fed and Feo. These findings provide valuable insights into the mechanisms involved in mitigating soil Cd bioavailability using integrated approaches with MV returning and lime materials.

Cadmium and calcium ions' effects on the growth of Pleurotus ostreatus mycelia are related to phosphatidylethanolamine content

Heavy metal Cd2+ can easily be accumulated by fungi, causing significant stress, with the fungal cell membrane being one of the primary targets. However, the understanding of the mechanisms behind this stress remains limited. This study investigated the changes in membrane lipid molecules of Pleurotus ostreatus mycelia under Cd2+ stress and the antagonistic effect of Ca2+ on this stress. Cd2+ in the growth media significantly inhibited mycelial growth, with increasing intensity at higher concentrations. The addition of Ca2+ mitigated this Cd2+-induced growth inhibition. Lipidomic analysis showed that Cd2+ reduced membrane lipid content and altered lipid composition, while Ca2+ counteracted these changes. The effects of both Cd2+ and Ca2+ on lipids are dose dependent and phosphatidylethanolamine appeared most affected. Cd2+ also caused a phosphatidylcholine/phosphatidylethanolamine ratio increase at high concentrations, but Ca2+ helped maintain normal levels. The acyl chain length and unsaturation of lipids remained unaffected, suggesting Cd2+ doesn't alter acyl chain structure of lipids. These findings suggest that Cd2+ may affect the growth of mycelia by inhibiting the synthesis of membrane lipids, particular the synthesis of phosphatidylethanolamine, providing novel insights into the mechanisms of Cd2+ stress in fungi and the role of Ca2+ in mitigating the stress.

Different stoichiometric ratios of Ca and Cd affect the Cd tolerance of Capsicum annuum L. by regulating the subcellular distribution and chemical forms of Cd

The effect of calcium (Ca)-cadmium (Cd) interactions on the plant Cd bioaccumulation process may be closely related to the ecological Ca/Cd stoichiometry in the substrate. However, owing to the complexity of plant absorption, accumulation mechanisms and influencing factors, the mechanism of Ca-mediated Cd bioaccumulation and Cd tolerance in Capsicum is still unclear. In this study, the bioaccumulation, subcellular distribution and chemical forms of Cd in Capsicum were analysed via pot experiments to reveal the Ca-mediated Cd bioaccumulation process and its detoxification mechanism under different Ca/Cd stoichiometric ratios. The results revealed that an increase in the substrate Ca/Cd ratio promoted the accumulation of Cd in the roots; restricted the transport of Cd to the stems, leaves and peppers; and promoted the accumulation of Cd in the aboveground leaves but decreased its accumulation in edible parts. Cd was enriched mainly in the cell wall and cell-soluble fraction in each tissue and was enriched in only 1 %-13 % of the organelles. The accumulation of Cd in the cell wall and cell-soluble fractions of roots treated with different Ca concentrations increased by 56.57 %-236.98 % and 64.41 %-442.14 %, respectively. The carboxyl, hydroxyl and amino groups on the root cell wall play important roles in binding and fixing Cd2+. Moreover, the increase in the Ca content also increased the proportion of pectin and protein-bound Cd (F-NaCl), insoluble phosphate-bound Cd (F-C) and insoluble oxalate-bound Cd (F-HCl) in the roots, stems and leaves and reduced the proportion of highly active chemical forms such as inorganic acid salt-bound Cd (F-E) and water-soluble phosphate-bound Cd (F-W). Our study revealed that the bioaccumulation of Cd in Capsicum was influenced by the Ca/Cd ratio and that Ca could alleviate Cd stress by regulating the subcellular distribution and chemical form ratio of Cd in different tissues where the cell wall plays an important role in Cd tolerance and detoxification.

Modulation of Cd carriers by innovative nanocomposite (Ca+Mg) and Cd-resistance microbes (Bacillus pumilus): a mechanistic approach to enhance growth and yield of rice (Oryza sativa L.)

Cadmium (Cd) is a well-known pollutant in agricultural soil, affecting human health through the food chain. To combat this issue, Ca + Mg (25 mg L-1) nanocomposite and Bacillus pumilus, either alone or combined, were applied to rice plants under Cd (5 mg kg-1, 10 mg kg-1) contamination. In our study, growth and yield traits demonstrated the beneficial influence of Ca + Mg and B. pumilus application in improving rice defense mechanism by reducing Cd stress. Combined Ca + Mg and B. pumilus application increased SPAD (15), total chlorophyll (18), chlorophyll a (11), chlorophyll b (22), and carotenoids (21%) with Cd (10 mg kg-1), compared to the application alone. Combined Ca + Mg and B. pumilus application significantly regulated MDA (15), H2O2 (13), EL (10), and O2 •- (24%) in shoots under Cd (10 mg kg-1), compared to the application alone. Cd (10 mg kg-1) increased the POD (22), SOD (21), APX (12), and CAT (13%) in shoots with combined Ca + Mg and B. pumilus application, compared to the application alone. Combined Ca + Mg and B. pumilus application significantly reduced Cd accumulation in roots (22), shoots (13), and grains (20%) under Cd (10 mg kg-1), compared to the application alone. Consequently, the combined application of Ca + Mg and B. pumilus is a sustainable solution to enhance crop production under Cd stress.

Joint utilization of Chinese milk vetch and lime materials mitigates soil cadmium risk and improves soil health in a double-cropping rice system

Cadmium (Cd) in paddy soil poses significant risks to humans due to its strong biological migration and toxicity. Chinese milk vetch (MV) is commonly used as green manure in the paddy fields of southern China and its potential to decrease the availability of Cd has been identified. Nevertheless, the effects of MV combined with lime materials (lime, L; limestone, LS) on Cd availability, soil properties, enzyme activity and comprehensive benefits are still not fully understood in double-cropping rice system. A field study was conducted to investigate these changes. The results indicated that all treatments notably decreased soil available Cd (Avail-Cd) by 19.3-44.3% and 14.9-43.1% during early and late rice, compared with CK. Moreover, the Cd fractions transformed to more stable forms. Compared to CK, all treatments reduced brown rice Cd content by 34.6-64.2% and 12.7-52.5% during the two periods. Furthermore, the translocation factors root to shoot, as well as shoot to brown rice, decreased. The combination led to improvements in soil properties, soil enzyme activity. Meantime, Cd in iron-manganese plaque (IMP) decreased by 31.9-51.1% and 29.0-42.7% respectively during two periods in amendments treatments. Soil pH and DOC were more important factors for Cd bioavailability than other properties. Additionally, rice Cd uptake was positively correlated with Cd in IMP. Enzyme activity exhibited a negative correlation with soil active Cd. Partial Least Squares Path Model (PLS-PM) indicated that the mitigation of Cd pollution helped to improve soil enzyme activity. Grey correlation analysis (GRA) indicated that MVLS showed the best comprehensive benefits in soil-plant system. Overall, the combination of MV and lime materials could reduce Cd availability, enhance soil properties and enzyme activity. And this could be strengthened by the combination. These findings will provide valuable insights for Cd-contaminated soil remediation.

Comparing the Effects of Lime Soil and Yellow Soil on Cadmium Accumulation in Rice during Grain-Filling and Maturation Periods

The karst area has become a high-risk area for Cadmium (Cd) exposure. Interestingly, the high levels of Cd in soils do not result in an excessive bioaccumulation of Cd in rice. Carbonate rock dissolution ions (CRIs) could limit the accumulation and translocation of Cd in rice. CRIs can become a major bottleneck in the remediation and management of farmlands in karst areas. However, there is limited research on the effects of CRIs in soils on Cd accumulation in rice. The karst area of lime soil (LS) and the non-karst areas of yellow soil (YS) were collected, and an external Cd was added to conduct rice cultivation experiments. Cd and CRIs (Ca2+, Mg2+, CO32-/HCO3-, and OH-) in the rice-soil system were investigated from the grain-filling to maturity periods. The results showed that CRIs of LS were significantly higher than that of YS in different treatments. CRIs of LS were 2.05 mg·kg-1 for Ca2+, 0.90 mg·kg-1 for Mg2+, and 42.29 mg·kg-1 for CO32- in LS. CRIs could influence DTPA Cd, resulting in DTPA Cd of LS being lower than that of YS. DTPA Cd of YS was one to three times larger than that of YS. Cd content in different parts of rice in YS was higher than that of LS. Cd in rice grains of YS was one to six times larger than that of LS. The uptake of Cd from the soil during Filling III was critical in determining rice Cd accumulation. CRIs in the soil could affect Cd accumulation in rice. Ca2+ and Mg2+ had significant negative effects on Cd accumulation of rice at maturity and filling, respectively. CO32-/HCO3- and OH- had significant negative effects on DTPA Cd in soil.

Biochar impacts on carbon dioxide, methane emission, and cadmium accumulation in rice from Cd-contaminated soils; A meta-analysis

Climate change and cadmium (Cd) contamination pose severe threats to rice production and food security. Biochar (BC) has emerged as a promising soil amendment for mitigating these challenges. To investigate the BC effects on paddy soil upon GHG emissions, Cd bioavailability, and its accumulation, a meta-analysis of published data from 2000 to 2023 was performed. Data Manager 5.3 and GetData plot Digitizer software were used to obtain and process the data for selected parameters. Our results showed a significant increase of 18% in soil pH with sewage sludge BC application, while 9% increase in soil organic carbon (SOC) using bamboo chips BC. There was a significant reduction in soil bulk density (8%), but no significant effects were observed for soil porosity, except for wheat straw BC which reduced the soil porosity by 6%. Sewage sludge and bamboo chips BC significantly reduced carbon dioxide (CO2) by 7-8% while municipal biowaste reduced methane (CH4) emissions by 2%. In the case of heavy metals, sunflower seedshells-derived materials and rice husk BC significantly reduced the bioavailable Cd in paddy soils by 24% and 12%, respectively. Cd uptake by rice roots was lowered considerably by the addition of kitchen waste (22%), peanut hulls (21%), and corn cob (15%) based BC. Similarly, cotton sticks, kitchen waste, peanut hulls, and rice husk BC restricted Cd translocation from rice roots to shoots by 22%, 27%, 20%, and 19%, respectively, while sawdust and rice husk-based BC were effective for reducing Cd accumulation in rice grains by 25% and 13%. Regarding rice yield, cotton sticks-based BC significantly increased the yield by 37% in Cd-contaminated paddy soil. The meta-analysis demonstrated that BC is an effective and multi-pronged strategy for sustainable and resilient rice cultivation by lowering greenhouse gas emissions and Cd accumulation while improving yields under the increasing threat of climate change.

Predicting Cd accumulation in rice and identifying nonlinear effects of soil nutrient elements based on machine learning methods

The spatial mismatch of Cd content in soil and rice causes difficulties in environmental management for paddy soil. To investigate the influence of soil environment on the accumulation of Cd in rice grain, we conducted a paired field sampling in the middle of the Xiangjiang River basin, examining the relationships between soil properties, soil nutrient elements, Cd content, plant uptake factor (PUFCd), and translocation factors in different rice organs (root, shoot, and grain). The total soil Cd (CdT) and available Cd (CdA) contents and PUFCd showed large spatial variability with ranges of 0.31-6.19 mg/kg, 0.03-3.07 mg/kg, and 0.02-3.51, respectively. Soil pH, CdT, CdA, and the contents of soil nutrient elements (Mg, Mn, Ca, P, Si, and B) were linearly correlated with grain Cd content (Cdg) and PUFCd. The decision tree analysis identified nonlinear effects of Si, Zn and Fe on rice Cd accumulation, which suggested that low Si and high Zn led to high Cdg, and low Si and Fe caused high PUFCd. Using the soil nutrient elements as predictor variables, random forest models successfully predicted the Cdg and PUFCd and performed better than multiple linear regressions. It suggested the impacts of soil nutrient elements on rice Cd accumulation should receive more attention.

Effects of blast furnace slag on the immobilization, plant uptake and translocation of Cd in a contaminated paddy soil

The potential toxicity of Cd to soil and rice plant severely threaten human health. This study was conducted to investigate the remediation effects of blast furnace slag (BFS) on the bioavailability of Cd in a contaminated paddy soil from a perspective of soil solution chemistry. Batch experiments, pot culture experiments, and principal analysis (PCA) were used to study the effects and mechanisms of BFS addition changing Cd chemical behavior and Cd toxicity. Results indicated that BFS facilitated Cd adsorption in soils, increased pH, Eh, and EC values in soil solution, whereas reduced dissolved Cd content. BFS amendment was efficient in decreasing root Cd intake and Cd upward transport in rice plant, with the Cd translocation factor in brown rice decreased by ∼ 75% (BFS treatment, 6‰ wt) relative to Cd treatment, which in turn increased rice biomass and grain yield. PCA indicated that the dissolved Cd concentration had a close relationship with soil pH and metal concentration in soil solution. Results from this study indicated that BFS had potential ability for either immobilization or remobilization of Cd in soils, and the findings have important implications for Cd-polluted soil remediation or other resource utilization with slag-based materials.

Different composites inhibit Cd accumulation in grains under the rice-oilseed rape rotation mode of karst area: A field study

Ensuring the safe production of food and oil crops in soils with elevated cadmium (Cd) content in karst regions is crucial. We tested a field experiment to examine the long-term remediation effects of compound microorganisms (CM), strong anion exchange adsorbent (SAX), processed oyster shell (POS), and composite humic acids (CHA) on Cd contamination in paddy fields under a rice-oilseed rape rotation system. In comparison to the control group (CK), the application of amendments significantly increased soil pH, cation exchange capacity (CEC), and soil organic matter (SOM) content while markedly decreasing the content of available Cd (ACd). During the rice cultivation season, Cd was predominantly concentrated in the roots. Relative to the control (CK), the Cd content in each organ was significantly reduced. The Cd content in brown rice decreased by 19.18-85.45%. The Cd content in brown rice following different treatments exhibited the order of CM > POS > CHA > SAX, which was lower than the Chinese Food Safety Standard (GB 2762-2017) (0.20 mg/kg). Intriguingly, during the oilseed rape cultivation season, we discovered that oilseed rape possesses potential phytoremediation capabilities, with Cd mainly accumulating in roots and stems. Notably, CHA treatment alone significantly decreased the Cd content in oilseed rape grains to 0.156 mg/kg. CHA treatment also maintained soil pH and SOM content, consistently reduced soil ACd content, and stabilized Cd content in RSF within the rice-oilseed rape rotation system. Importantly, CHA treatment not only enhances crop production but also has a low total cost (1255.230 US$/hm2). Our research demonstrated that CHA provides a consistent and stable remediation effect on Cd-contaminated rice fields within the crop rotation system, as evidenced by the analysis of Cd reduction efficiency, crop yield, soil environmental change, and total cost. These findings offer valuable guidance for sustainable soil utilization and safe production of grain and oil crops in the context of high Cd concentrations in karst mountainous regions.

Effect of amendments on bioavailability of cadmium in soil-rice system: a field experiment study

The field experiment study investigated the effect of lime (L), manure compost (M), combination of lime and manure (LM), and combinations of lime with four kinds of passivators (LP1, LP2, LP3, and LP4) on the bioavailability of cadmium (Cd) in soil and Cd accumulation in rice plants. These four passivating products were composed of organic and inorganic compounds such as silicon-sulfhydryl group, CaO, SiO₂, and so on. The results indicated that the application of these amendments improved soil pH, organic matter content, and cation exchange capacity (CEC) by 0.19-0.73 unit, 0.6-8.2%, and 5.7-38.9%, respectively; meanwhile, decreased soil acid-extractable Cd by 4.0-13.9% compared with before remediation. Alleviating Cd stress to rice also resulted in a significant increase in rice grains yield, whereas the LP4 showed an increment of 15.8-27.6%. Among these amendments, LP4 had a relatively high effectiveness, it promoted the decrease of extractable Cd by 13.9% and the increase of residual Cd by 8.1%; meanwhile, the bioconcentration factor of rice grain in LP4 decreased by 71.3%. The high pH, CEC, and rich functional groups in amendments might cause soil Cd transform from mobile fraction to residual fraction, and the cation ions in amendments also competed with Cd ions due to the antagonism. Taken all of these effects, the amendments alleviated Cd pollution in soil-rice system, decreasing Cd migration from soil to grain. In future, the long-term field experiment will need to be done for verify the long-term effect of soil amendments.

De Novo transcriptome combined with physiological analyses revealed key genes for cadmium accumulation in Zhe-Maidong (Ophiopogon japonicus)

INTRODUCTION

Cadmium (Cd) is a toxic heavy metal that severely threatens safe food production. Zhe-Maidong, a well-known Chinese traditional herbal medicine, is susceptible to Cd stress. However, the characteristics of Cd transformation and migration, as well as the regulatory system for genes conferring Cd accumulation of Zhe-Maidong, remains an essential issue to be addressed.

METHODS

Zhe-Maidong seedling growth in Cd-contaminated and uncontaminated soil was conducted for 90 days. The Cd concentration was determined by inductively coupled plasma-mass spectrometry, and the Cd²⁺ fluorescence probe detected Cd distributions. The root transcriptome of Zhe-Maidong was then evaluated using various Cd stress hydroponic treatments designated Cd-0, Cd-M, and Cd-H.

RESULTS AND DISCUSSION

The enrichment factor (EF) value in the root was four times that of the leaves, indicating that the root has a high ability to absorb and accumulate Cd. The Cd²⁺ were mainly distributed in the root hair and the epidermis in both roots and leaves, revealing that the epidermal cells of roots may collect Cd²⁺ and also have an outstanding role in Cd²⁺ uptake. A total of 50 DEGs involved in Cd translocation and accumulation were identified. Among these DEGs, ANN, ABCC2/4, HMA1- 5, and CCX gene expression were positively correlated with EF-root, EF-leaf, EF-total, Cd-leaf, Cd-root, and Cd-plant, indicating their role in Cd transport and accumulation under Cd-stress. These data could be helpful in uncovering the Cd accumulation characteristics in Zhe-Maidong, as well as provide a bioinformatic foundation for investigations on finding gene functions and the screening of candidate genes related to Cd accumulation.