Search Results (102)

This investigation examines the influence of P. dabryanus density on the growth performance of P. nigromaculatus and the structural and functional dynamics of paddy soil microbial communities within a rice–frog–loach integrated aquaculture system. Field experiments were conducted with five density gradients of P. dabryanus (0.5, 1.0, 1.5, 2.0, and 2.5 × 10⁴ individuals/667 m²), designated as RFLS0.5, RFLS1.0, RFLS1.5, RFLS2.0, and RFLS2.5, respectively. Control treatments included rice monoculture (RM) and rice–frog co-culture (RFS). These findings demonstrated that as the density of loach increased, the weight gain ratio of P. nigromaculatus showed a unimodal pattern, reaching its peak in RFLS1. Metagenomic analysis on paddy soil revealed that the RFLS1 facilitated the enrichment of nitrogen-fixing bacteria (Proteobacteria), while concurrently suppressing proliferation of the potential pathogen Pseudomonas aeruginosa and microbial markers in metal-contaminated environments of Usitatibacter rugosus. Further, functional profiling indicated that RFLS1 group reached a peak activity in amino acid metabolism (14.52 ± 0.09%) and carbohydrate metabolism (14.44 ± 0.06%) and showed a higher proportion of glycosyltransferase (GT) abundance (41.93 ± 0.02%) than other groups. In summary, the optimal stocking density of P. dabryanus in rice–frog–loach integrated systems was determined to be 1.0 × 10⁴ individuals/667 m². This density not only promotes the growth of P. nigromaculatus but also improves the structure of paddy soil microbial communities. Full article

Arsenic (As) and cadmium (Cd) in rice grains are major global food safety concerns. Iron (Fe) can help reduce both, but current Fe treatments suffer from poor stability, low leaf absorption, and fast soil immobilization, with unclear underlying mechanisms. To address these issues, an Fe-based metal–organic framework (MIL-88) was modified with sodium alginate (SA) to form MIL-88@SA. Its stability as a foliar inhibitor and its leaf absorption were tested, and its effects on As and Cd accumulation in rice were compared with those of soluble Fe (FeCl₃) and chelating Fe (HA + FeCl₃) in a field study on As–Cd co-contaminated rice paddies. Compared with the control, MIL-88@SA outperformed or matched the other Fe treatments. A single foliar spray during the tillering stage increased the rice yield by 19% and reduced the inorganic As and Cd content in the grains by 22.8% and 67.8%, respectively, while the other Fe treatments required two sprays. Its superior performance was attributed to better leaf affinity and thermal stability. Laser ablation inductively coupled plasma–mass spectrometry (LA–ICP–MS) and confocal laser scanning microscopy (CLSM) analyses revealed that Fe improved photosynthesis and alleviated As–Cd stress in leaves, MIL-88@SA promoted As and Cd redistribution, and Fe–Cd co-accumulation in leaf veins enhanced Cd retention in leaves. Full article

Heavy metal contamination in paddy fields poses serious risks to food safety and crop productivity. This study evaluated the potential of native soil fungi as bioinoculants to reduce metal uptake in rice cultivated under contaminated conditions. Eight fungal strains—four indigenous and four allochthonous—were selected based on their plant growth-promoting traits, including siderophore production and phosphate solubilization. Additional metabolic analysis confirmed the production of bioactive secondary metabolites. In a greenhouse experiment, three rice cultivars were grown under permanent flooding (PF) and alternate wetting and drying (AWD) in soil enriched with arsenic, cadmium, chromium, and copper. Inoculation with indigenous fungi under AWD significantly reduced the arsenic accumulation in rice shoots by up to 75%. While AWD increased cadmium uptake across all cultivars, fungal inoculation led to a moderate reduction in cadmium accumulation—ranging from 15% to 25%—in some varieties. These effects were not observed under PF conditions. The results demonstrate the potential of native fungi as a nature-based solution to mitigate heavy metal stress in rice cultivation, supporting both environmental remediation and sustainable agriculture. Full article

The co-contamination of arsenic (As) and cadmium (Cd) in paddy soils threatens rice safety, yet synergistic mitigation strategies using silicon (Si) and ferrous sulfate (FeSO₄) remain underexplored. This study integrated hydroponic and soil pot experiments to evaluate Si-FeSO₄ interactions on As/Cd accumulation and rice growth. Hydroponic trials employed 21-day-old rice seedlings exposed to 0.5 mg As(III)/Cd(II) L⁻¹ with/without 70 mg Si L⁻¹ and 30–70 mg Fe L⁻¹, followed by sequential harvesting at 14 and 21 days. Soil experiments utilized co-contaminated paddy soil (50 mg As kg⁻¹ and 1.2 mg Cd kg⁻¹) amended with Si (80 or 400 mg kg⁻¹) and Fe (100 or 1000 mg kg⁻¹), with pore water dynamics monitored over 120 days. Hydroponic results demonstrated that 70 mg Si L⁻¹ combined with 30 or 70 mg Fe L⁻¹ enhanced shoot biomass by 12–79% under As stress, while simultaneously reducing shoot As concentrations by 76–87% and Cd concentrations by 14–33%. Iron plaque induced by FeSO₄ exhibited contrasting adsorption behaviors: hydroponic roots immobilized both As and Cd (p < 0.01), whereas roots in soil primarily retained Cd (p < 0.05). In soil experiments, the optimal treatment of 100 mg Fe kg⁻¹ and 400 mg Si kg⁻¹ (Fe₁ + Si₂) increased grain biomass by 54%, while reducing As and Cd concentrations by 37% and 42%, respectively. However, a higher Fe dosage (Fe₂: 1000 mg kg⁻¹ Fe) paradoxically increased grain Cd concentrations. Mechanistically, Si amendment elevated soil pH (Δ + 0.72), facilitating Cd immobilization, while FeSO₄ lowered pH (Δ−0.07–0.53), increasing Cd mobility. A strong correlation between soluble Cd and plant uptake was observed (p < 0.01), while changes in As accumulation were unrelated to aqueous behavior. The optimized Si/Fe molar ratio of 7.95:1 effectively mitigated As and Cd co-accumulation, offering a dual-functional strategy for safe rice cultivation in contaminated soils. Full article

(1) Background: Road traffic emissions significantly influence heavy metal accumulation in roadside agricultural soils, posing risks to food safety. (2) Methods: This study investigated the concentrations of heavy metals (As, Cd, Cu, Cr, Hg, Ni, Pb, and Zn) in paddy soils at 96 soil samples along National Highways G107 and G312 in southern Henan, China, to evaluate the contamination situation and ecological risks using a multimetric approach. (3) Results: Cd, Hg, Cu, and Zn exceeded provincial background levels. Cd dominated contamination, showing heavy pollution (single factor index, P_i > 5) within 40 m of G107 and moderate/heavy levels (P_i = 2–5) along G312. The Nemerow index (P_N) classified both highways as slightly polluted (P_N = 0.70–0.81), with higher contamination along G107. Geoaccumulation indices identified Cd as mildly/moderately polluted within 40 m of G107 and G312 and Zn as slightly contaminated within 20–40 m of G107. Despite low total ecological risk, Cd contributed >75% to cumulative risk due to its high toxicity (Tr = 30). (4) Conclusions: Road traffic constitutes one of the contributors to heavy metal accumulation in paddy soils along national highways in southern Henan Province, while agricultural cultivation adjacent to transportation corridors poses potential food safety risks. Full article

Cadmium (Cd) contamination in paddy soils severely threatens rice safety and human health. Currently, the high costs and technical barriers of existing Cd remediation methods limit their development, so it’s urgent to find an economical and feasible method. Herein, the synergistic effects of rhodochrosite slag and biochar on Cd immobilization in slightly acidic Cd-contaminated paddy soils have been investigated. A field experiment with four treatments—control (CK), rhodochrosite slag (R), biochar (B), and combined rhodochrosite slag + biochar (RB)—was conducted in Hunan Province, China. Results demonstrated that RB treatment significantly increased soil pH, transferred the mobile Cd to the residual fraction, and reduced Cd availability in the soil. Cd concentrations in rice roots, stems, leaves, and brown rice decreased by 26.37%, 47.20%, 31.03%, and 51.85%, respectively, under RB treatment, achieving the lowest TF and BCF values. Furthermore, RB treatment increased rice yield by 18.73%. The synergistic interaction between biochar’s adsorption capacity and rhodochrosite slag-derived competitive ions effectively transformed Cd into stable fractions, reducing bioavailability. This study proposes a novel remediation strategy that not only enhances the Cd immobilization ability of biochar but also achieves simultaneous waste valorization and soil remediation. Full article

The contamination of paddy soils with arsenic (As) and cadmium (Cd), coupled with the depletion of soil organic carbon (SOC), poses significant threats to rice yields and quality. There is an urgent need to identify a suitable soil additive capable of achieving simultaneous heavy metal remediation and promotion of organic matter enrichment. The current study introduced two novel iron (Fe)/magnesium (Mg)-based bimetal-oxide-modified rice straw biochar (RSB), namely RSB-Fe/Mn and RSB-Fe/Mg. It evaluated their effectiveness in As/Cd immobilization and SOC preservation. An 8-week cultivation experiment was carried out in sequential drying–flooding moisture fluctuation conditions, with the soil pore water As/Cd (PWAs/Cd) and SOC fractions monitored. The mechanisms of As/Cd immobilization were investigated using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) characterizations. Results revealed that PWAs and PWCd were reduced by up to 67.1% and 80.2% during the drying period and by 27.0% and 76.5% during the flooding period, respectively. Additionally, SOC content increased by 16.3% and 33.9% with RSB-Fe/Mn addition during the drying and flooding period, respectively, with an increase in the mineral-associated organic carbon (MAOC) fraction. The study proves that RSB-Fe/Mn and RSB-Fe/Mg are effective for soil As/Cd passivation and SOC stabilization, offering a promising solution to mitigate As and Cd pollution in paddy soils while maintaining soil quality. Full article

Potentially toxic elements (PTE), such as cadmium (Cd), lead (Pb), and arsenic (As), threaten rice (Oryza sativa L.) crop productivity and pose significant risks to human health when they are present in soil. This review summarizes the current understanding of soil and rice contamination with As, Cd, and Pb to provide an in-depth understanding of the dynamics of these contaminants and the mechanisms regulating their flow from soil to plants. It focuses on the following aspects: (1) these metals’ geochemical distribution and speciation in soil–rice systems; (2) factors influencing the transformation, bioavailability, and uptake of these metals in paddy soils; (3) metal uptake, transport, translocation, and accumulation mechanisms in rice grains; and (4) the roles of transporters involved in metal uptake, transport, and accumulation in rice plants. Moreover, this review contributes to a clearer understanding of the environmental risks associated with these toxic metals in soil–rice ecosystems. Furthermore, it highlights the challenges in simultaneously managing the risks of As, Cd, and Pb contamination in rice. The study findings may help inspire innovative methods, biotechnological applications, and sustainable management strategies to mitigate the accumulation of As, Cd, and Pb in rice grains while effectively addressing multi-metal contamination in paddy soils. Full article

Cadmium (Cd) pollution in paddy soils causes a great threat to safe rice production in China. In this review, we summarized the key advances in the research of Cd pollution sources and statuses in Chinese soil and rice, explore the mechanisms of Cd transformation in the rice–soil system, discuss the agronomic strategies for minimizing Cd accumulation in rice grains, and highlight advancements in developing rice cultivars with low Cd accumulation. Anthropogenic activity is a main source of Cd in farmland. Cd in soil solutions primarily enters rice roots through a symplastic pathway facilitated by transporters like OsNRAMP5, OsIRT1, and OsCd1, among which OsNRAMP5 is identified as the primary contributor. Subsequently, Cd translocation is from roots to grains through the xylem and phloem, regulated by transporters such as OsHMA2, OsLCT1, and OsZIP7. Meanwhile, Cd sequestration in vacuoles controlled by OsHMA3 plays a crucial role in regulating Cd mobility during its translocation. Cd accumulation in rice was limited by the available Cd concentration in soil solutions, Cd uptake, and translocation in rice plants. Conventional agronomic methods aimed at reducing grain Cd in rice by suppressing Cd bio-availability without decreasing soil Cd content have been proven limited in the remediation of Cd-polluted soil. In recent years, based on the mechanisms of Cd absorption and translocation in rice, researchers have screened and developed low-Cd-accumulation rice varieties using molecular breeding techniques. Among them, some new cultivars derived from the null mutants of OsNRAMP5 have demonstrated a more than 93% decrease in grain Cd accumulation and can be used for applications in the next years. Therefore, the issue of Cd contamination in the rice of China may be fully resolved within a few years. Full article

Alkaline fertilizers demonstrate significant potential in mitigating rice cadmium (Cd) accumulation, yet the combined effects of calcium–magnesium phosphate (CMP) with potassium (K) fertilizer types and split application strategies remain unclear. Through multi-site field trials in Cd-contaminated paddy soils, we evaluated split applications of K₂CO₃, K₂SO₄, and K₂SiO₃ at tillering and booting stages following basal CMP amendment. Optimized K regimes reduced brown rice Cd concentrations (up to 89% reduction) compared to conventional fertilization. Notably, at the CF site, split K₂SiO₃ application (TB-K₂SiO₃) and single tillering-stage K₂SO₄ (T-K₂SO₄) achieved brown rice Cd levels of 0.13 mg/kg, complying with China’s food safety standard (≤0.20 mg/kg), thereby eliminating non-carcinogenic risks. Mechanistically, TB-K₂SiO₃ enhanced soil pH by 0.21 units and increased available K (AK) by 50.26% and available Si (ASi) by 21.35% while reducing Cd bioavailability by 43.55% compared to non-split K₂SiO₃. In contrast, T-K₂SO₄ elevated sulfate-driven Cd immobilization. Structural equation modeling prioritized soil available Cd, root Cd, and antagonistic effects of AK and ASi as dominant factors governing Cd accumulation. The integration of CMP with split K₂SiO₃ application at the tillering and booting stages or single K₂SO₄ application at the tillering stage ensures safe rice production in Cd-contaminated soils, offering scalable remediation strategies for paddy ecosystems. Full article

Microplastics have a large surface area and hydrophobic characteristics, which helps them to easily adsorb organic matter and trace metals in soil. This interaction has the potential to alter soil physicochemical properties, affect the bioavailability of metals, and finally influence the toxicity of organisms. In the present study, we exposed Cd or As (Cd/As) to the earthworm Eisenia fetida (Savigny, 1826) in uncontaminated paddy soil, both in the presence and absence of polystyrene (PS) MPs (100~300 μm). The results show that MPs exhibit a significant influence on the physicochemical properties of As-contaminated soil, notably reducing the pH while increasing the electrical conductivity (EC), redox potential (Eh), and dissolved organic carbon (DOC), relative to single As treatment. At a Cd concentration of 40 mg·kg⁻¹, the addition of MPs substantially altered the soil properties, decreasing the pH while increasing the EC and DOC. The effect of MPs on the bioavailable Cd content in soil was associated with Cd concentration. Specifically, MPs significantly increased the content of DGT (diffusion gradient technology)-Cd at a Cd concentration of 60 mg·kg⁻¹. Regarding the bioavailable As content in the soil, MPs led to an increase at a high As concentration (40 mg·kg⁻¹). Moreover, the addition of MPs amplified the uptake rate constants (k_u) of DGT-Cd/As at various exposure concentrations, expediting the uptake of Cd/As by earthworms. In addition, compared to Cd treatment, the growth inhibition of earthworms in the As-treatment group was more significant due to microplastics. The results show that MPs in terrestrial environments magnify the negative effects of (semi-)metals, a phenomenon intricately tied to the degree of contamination by (semi-)metals. The interaction between MPs and metals may induce higher ecological risks for organisms. Full article

Biochar is a stabilised, carbon-rich material created when biomass is heated to temperatures usually between 450 and 550 °C, under low-oxygen concentrations. This study evaluated the effectiveness of sawdust, cocoa pod ash and rice husk biochars in remediating metal-contaminated paddy soil in Nobewam, Ghana. Biochar was applied 21 days before cultivating the rice for 120 days, followed by soil sampling and rice harvesting for metals and physicochemical analyses. Compared to the untreated soils, biochar treatments exhibited an enhancement in soil quality, characterised by an increase in pH of 1.01–1.20 units, an increase in available phosphorus (P) concentration of 6.76–13.05 mg/kg soil and an increase in soil total nitrogen (N), and organic carbon (OC) concentration, ranging from 0.02% to 0.12%. Variabilities in electrical conductivity and effective cation exchange capacity were observed among the treated soils. Concentrations of potentially toxic metals (arsenic, cadmium, copper, mercury, lead and zinc) in paddy soils and rice analysed by atomic absorption spectroscopy showed significant differences (p < 0.05) among the sampled soils. The concentrations of arsenic and lead in all soil samples exceeded the Canadian Council of Ministers of the Environment soil quality guideline for agricultural soils, with untreated soils having the highest levels among all the soils. Cadmium had a potential ecological risk index > 2000 and a geoaccumulation index above 5, indicating pollution in all samples. In contrast, arsenic and mercury contamination were only found in the untreated soils. Among the tested treatments, rice husk and its combinations, particularly with cocoa pod ash, showed significant efficacy in reducing metal concentrations in the soils. The potential non-carcinogenic human health risks associated with the consumption of rice grown in biochar-treated soils were lower for all the metals compared to the control samples. Future research should focus on long-term field studies to validate these findings and explore the underlying mechanisms governing metal immobilization in paddy fields. Full article

17β-estradiol (E2) contamination resulting from the widespread use of animal manure poses a new threat to the agricultural environment. Since anaerobic environments have been reported to significantly extend the persistence of E2, estrogen pollution of anaerobic farmland soils (e.g., paddy soils) is of particular concern, necessitating the development of in situ high-efficiency E2 bioremediation microorganisms. In this work, six E2-degrading strains were isolated from paddy soils, including strains from Elizabethkingia, Stenotrophomonas, Microbacterium, Ochrobactrum, Gordonia, and Acinetobacter. Among these strains, Ochrobactrum sp. AEPI-SP11 and Acinetobacter sp. AEPI-SP17 were able to degrade over 90% of 20 mg/L E2 within 5 days. Although both AEPI-SP11 and AEPI-SP17 exhibited strong tolerance to pH, temperature, and initial E2 concentrations (2, 5, 20, and 50 mg/L), only AEPI-SP17 was capable of biodegrading E2 under anaerobic conditions. Based on genomic analysis, we further obtained the whole genome sequences of AEPI-SP11 and AEPI-SP17 and identified and compared potential genes responsible for estrogen degradation in the two strains. Overall, this work significantly enhances our understanding of E2-degrading strains in paddy soils, offers valuable insights into the degradation mechanisms under varying conditions, and provides potential microbial resources for the effective control of E2 pollution in farmlands. Full article

The unreasonable application of nitrogen (N) fertilizer leads to high nutrient losses and severe potential of agricultural non-point source contamination, which threatens water quality in the upper Yellow River Basin. Therefore, the aim of this study is to explore the effects of N application rates and various control measures on rice yield and N leaching in paddy fields in the Yellow River irrigation area. Four treatments were employed in this study, CK (no N fertilizer application, 0 kg N∙ha⁻¹), CRU (controlled-release urea application, 180 kg N∙ha⁻¹), OPT (optimal N fertilizer application, 210 kg N∙ha⁻¹), and FP (N fertilizer application based on farmer experience, 240 kg N∙ha⁻¹), to examine paddy yield, N use efficiency (NUE), N concentrations in leaching water at various soil depths, and N contents along the 0–100 cm depth of the soil profile. The results indicated that the amount of TN leached was 25.14–48.04 kg∙ha⁻¹ after different N applications, and the TN leaching coefficients of FP, OPT, and CRU were 10.88%, 11.27%, and 7.07%. Compared to FP and OPT, the CRU significantly reduced the concentrations of TN, ammonium N (NH₄⁺-N), and nitrate N (NO₃⁻-N) in the surface and soil water, with average TN leaching decreasing by 31.55% and 27.35% in the years 2022 and 2023, respectively. NO₃⁻-N was identified as the primary form of N leached from the paddy fields. Compared to FP and OPT treatments, the CRU treatment increased the average paddy yield by 19.99–20.66% and improved the average NUE by 19.04–16.38%. This study revealed that the application of high amounts of N positively affected soil N leaching, and controlled-release urea demonstrates superior efficacy compared to conventional fertilization. The application of controlled-release urea at a rate of 180 kg N∙ha⁻¹ not only ensures a good paddy yield but also reduce N losses, which should be recommended to local farmers. Full article

Bioremediation is widely recognized as a promising and efficient approach for the elimination of Cd from contaminated paddy soils. However, the Cd removal efficacy achieved through this method remains unsatisfactory and is accompanied by a marginally higher cost. Cysteine has the potential to improve the bioleaching efficiency of Cd from soils and decrease the use cost since it is green, acidic and has a high Cd affinity. In this study, different combination modes of cysteine and microbial inoculant were designed to analyze their effects on Cd removal and the soil microbial community through the sequence extraction of Cd fraction and high-throughput sequencing. The results demonstrate that the mixture of cysteine and the microbial inoculant was the best mode for increasing the Cd removal efficiency. And a ratio of cysteine to microbial inoculant of 5 mg:2 mL in a 300 mL volume was the most economically efficient matching. The Cd removal rate increased by 7.7–15.1% in comparison with the microbial inoculant treatment. This could be ascribed to the enhanced removal rate of the exchangeable and carbonate-bound Cd, which achieved 94.6% and 96.1%, respectively. After the treatment, the contents of ammonium nitrogen (NH₃–N), total phosphorus (TP), available potassium (AK), and available phosphorus (AP) in the paddy soils were increased. The treatment of combinations of cysteine and microbial inoculant had an impact on the soil microbial diversity. The relative abundances of Alicyclobacillus, Metallibacterium, and Bacillus were increased in the paddy soils. The microbial metabolic functions, such as replication and repair and amino acid metabolism, were also increased after treatment, which benefitted the microbial survival and adaptation to the environment. The removal of Cd was attributed to the solubilizing, complexing, and ion-exchanging effects of the cysteine, the intra- and extracellular adsorption, and the production of organic acids of functional microorganisms. Moreover, cysteine, as a carbon, nitrogen, and sulfur source, promoted the growth and metabolism of microorganisms to achieve the effect of the synergistic promotion of microbial Cd removal. Therefore, this study underscored the potential of cysteine to enhance the bioremediation performance in Cd-contaminated paddy soils, offering valuable theoretical and technical insights for this field. Full article