Subsurface drip irrigation reduces cadmium accumulation of pepper (Capsicum annuum L.) plants in upland soil

Simulating the effects of drip and flood irrigation on the leaching, migration, and redistribution of heavy metals in contaminated soil

BACKGROUND

The extensive adoption of drip irrigation globally has adverse effects on the ecological integrity of soil, leading to significant changes in the distribution of heavy metals and other pollutants across various soil layers. However, the mechanisms underlying such changes are still unclear.

PURPOSE

This study explores the effects of different irrigation methods (drip and flood irrigation) on the heavy metal behaviors in contaminated soils, including leaching, migration, and redistribution within agricultural practices.

MATERIALS AND METHODS

The soil column leaching experiments simulating drip and flood irrigation were performed. The correlation tests and one-way analysis of variance were used for data analysis.

RESULTS

Compared to flood irrigation, drip irrigation resulted in higher leaching; as high as twice of heavy metal redistribution across soil columns. The average changes in heavy metal concentration before and after drip irrigation and flood irrigation were 16.3 % and 3.3 %, respectively. The soil redox potential and contact time were the main factors affecting the migration of heavy metals during the initial stages of irrigation implementation; however, hydrodynamic factors were also influential.

CONCLUSION

Drip irrigation may pose a serious threat to food safety in the areas with considerable heavy metal pollution due to increased heavy metal leaching and the accumulation of heavy metals near the soil surface, in particular at lower water volume.

Enhancing soil quality in soybean cultivation: Mycorrhizal technology combined with intercropping under high cadmium stress

Cadmium (Cd) contamination presents a serious challenges for sustainable agriculture. This study evaluated the combined impact of arbuscular mycorrhizal fungi (AMF) inoculation and intercropping with Solanum nigrum on soil microbial diversity, enzyme activity, and environmental factors in soybean cultivation under high Cd stress. The combined treatment effectively reduced bioavailable Cd in soil, with the acid-soluble Cd fraction at 19.57 mg/kg and the reducible Cd fraction at 61.35 %, resulting in safe soybean grain Cd levels (2.63 mg/kg, below the 3 mg/kg organic standard). Illumina NovaSeq sequencing analysis revealed that key bacterial taxa, including Bradyrhizobium and PMMR1, were correlated with reduced Cd uptake in grains. Although bacterial α diversity increased, microbial network stability decreased in response to Cd, AMF inoculation, and intercropping. The combined treatment also enhanced soil enzyme activity by regulating the relative abundance of dominant or key genera such as Subgroup_6, Rokubacteriales and Pseudarthrobacter. Notably, catalase activity was 97.25 % higher in the combined treatment compared to monoculture without AMF colonization under high Cd conditions. These findings demonstrate the synergistic potential of AMF inoculation and S. nigrum intercropping as a sustainable approach to mitigate Cd contamination in crops while improving soil health in Cd-contaminated environments.

Comprehensive approach integrating remote sensing, machine learning, and physicochemical parameters to detect hydrodynamic conditions and groundwater quality deterioration in non-rechargeable aquifer systems

The current study integrates remote sensing, machine learning, and physicochemical parameters to detect hydrodynamic conditions and groundwater quality deterioration in non-rechargeable aquifer systems. Fifty-two water samples were collected from all water resources in Siwa Oasis and analyzed for physical (pH, T°C, EC, and TDS) chemical (SO4 2-, HCO3 -, NO3 -, Cl-, CO3 2-, SiO2, Mg2+, Na+, Ca2+, and K+), and trace metals (AL, Fe, Sr, Ba, B, and Mn). A digital elevation model supported by machine learning was used to predict the change in the land cover (surface lake area, soil salinity, and water logging) and its effect on water quality deterioration. The groundwater circulation and interaction between the deep aquifer (NSSA) and shallow aquifer (TCA) were detected from the pressure-depth profile of 27 production wells penetrating NSSA. The chemical facies evolution in the aquifer systems were (Ca-Mg-HCO3) in the first stage (freshwater of NSSA) and changed to (Na-Cl) type in the last stage (brackish water of TCA and springs). Support vector machine successfully predicted the rapid increase of the hypersaline lake area from 22.6 km2 to 60.6 km2 within 30 years, which deteriorated a large part of the cultivated land, reflecting the environmental risk of over-extraction of water for irrigation of agricultural land by flooding technique and lack of suitable drainage network. The waterlogging in the study was due to a reduction in the infiltration rate (low permeability) of the soil and quaternary aquifer. The cause of this issue could be a complete saturation of agricultural water with chrysotile, calcite, talc, dolomite, gibbsite, chlorite, Ca-montmorillonite, illite, hematite, kaolinite and K-mica (saturation index >1), giving the chance of these minerals to precipitate in the pore spaces of the soil and decrease the infiltration rate. The NSSA is appropriate for irrigation, whereas TCA is inappropriate due to potential salinity and magnesium risks. The best way to manage water resources in Siwa Oasis could be to use underground drip irrigation and combine water with TCA and NSSA.

Optimized sand tube irrigation combined with nitrogen application improves jujube yield as well as water and nitrogen use efficiencies in an arid desert region of Northwest China

Efficient water-saving irrigation techniques and appropriate nitrogen (N) application are keys to solving the problems of water scarcity and irrational fertilization in jujube cultivation. In this study, first, the effects of sand tube irrigation (STI) on surface and subsurface wetted characteristics were investigated using in-situ infiltration tests in a jujube garden. Compared with surface drip irrigation (SD), STI reduced surface wetted area by 57.4% and wetted perimeter of the surface wetted circle by 37.1% and increased subsurface maximum infiltration distance of wetting front by 64.9%. At the optimal sand tube depth of 20 cm, surface wetted area of the surface wetted circle decreased by 65.4% and maximum infiltration distance of the wetting front increased by 70.9%, compared with SD. Two-year field experiments then investigated the effects of STI and SD on soil water storage, jujube leaf chlorophyll, net photosynthetic rate, actual water consumption, fruit yield, and water (WUE) and N (NUE) use efficiencies at four levels of N (pure nitrogen: N1, 0; N2, 286 kg ha-1; N3, 381 kg ha-1; N4, 476 kg ha-1) at the same irrigation amount (45 mm irrigation-1, total of 8). Compared with SD, STI increased soil water storage 18.0% (2021) and 15.6% (2022) during the entire growth period and also chlorophyll content, nitrogen balance index, and net photosynthetic rate, with both increasing and then decreasing with increasing N. Compared with SD, STI increased yields by 39.1% and 36.5% and WUE by 44.3% and 39.7% in 2021 and 2022, respectively. Nitrogen use efficiency was 2.5 (2021) and 1.6 (2022) times higher with STI than with SD. STI combined with N3 had the highest yield, WUE, NUE, and net income and is thus recommended as the optimal water-N combination. In conclusion, STI combined with appropriate N application can be an effective water-saving irrigation technology alternative to SD in jujube cultivation in arid areas.

Physiological and biochemical characteristics of high and low Cd accumulating Brassica napus genotypes

Phytoremediation is a widely used and cost-effective technique for in situ remediation of heavy metals. Brassica napus L. genotype with high Cd accumulation and strong Cd tolerance is an ideal candidate for phytoremediation. In this study, a hydroponic experiment was conducted to select a Brassica napus genotype with either high or low Cd accumulation from a panel of 55 genotypes. The physiological mechanisms governing Cd accumulation and Cd tolerance were then explored. BN400 and BN147 were identified as the high and low Cd accumulating genotypes, respectively. Additionally, BN400 exhibited greater tolerance to Cd stress compared to BN147. Root morphology analysis revealed that BN400 exhibited longer root length, smaller root surface area and root volume, and less root tips but bigger root diameter than BN147. Subcellular Cd distribution showed that the Cd concentrations in the cell wall and vacuole in shoot were significantly higher in BN400 than in BN147, whereas the opposite trend was observed in the roots.. Pectate/protein-integrated Cd was found to be the predominant form of Cd in both shoots and roots, with significantly higher levels in BN400 compared to BN147 in the shoot, but the opposite trend was observed in the roots. These results suggest that the long fine roots play a role in Cd accumulation. The high Cd accumulating genotype was able to retain Cd in leaf cell walls and vacuoles, and Cd was mainly present in the form of pectate/protein-integrated Cd, which contributes to its strong Cd tolerance. These findings have important implications for the screening and breeding of Brassica napus genotypes with high Cd accumulation for phytoremediation purposes.

Effect of boron supply on the uptake and translocation of cadmium in Capsicum annuum

Large areas of soil in southern China are contaminated with cadmium (Cd) and are deficient in boron (B). Previously, we suggested that B supplementation could reduce Cd accumulation in hot peppers (Capsicum annuum L.); however, the physiological mechanisms underlying this reduction remain unclear. In this study, the uptake and translocation of Cd in hot pepper plants were investigated using hydroponic experiments with different B and Cd treatments. A pot experiment was performed to verify whether B decreased the Cd concentration in hot peppers by minimizing the Cd translocation rate. The results of the dose- and time-dependent experiments showed that B supplementation reduced root Cd uptake and root-to-shoot Cd translocation. Additionally, B supplementation increased the root length, diameter, volume, surface area, and number of root forks and tips, as well as improving the relative absorbance of carboxyl groups under Cd exposure, leading to enhanced Cd fixation in the cell walls of the roots. As a result, the fruit Cd concentration decreased because B inhibited Cd translocation from the roots. Overall, the results demonstrate that B supplementation can reduce Cd accumulation in hot peppers by promoting normal root growth and development and by limiting the uptake and translocation of Cd.

Organic-inorganic composite modifiers enhance restoration potential of Nerium oleander L. to lead-zinc tailing: application of phytoremediation

Lead-zinc tailings are complex heavy metal solid wastes produced in the mining process. In this study, two kinds of organic-inorganic mixed improvers mushroom residue + calcium carbonate (M + C) and peat soil + calcium carbonate (N + C) were selected. Then, the effect of two improvers and a woody plant, Nerium oleander L., on the combined remediation of lead-zinc tailings was compared, respectively. The results showed that two combined improvers can slightly improve the pH of tailing, significantly increase the activity of phosphatase and catalase, effectively reduce the contents of DTPA-extractable Pb and Zn, and significantly improve the structure of tailing. However, the improvement effect of M + C was better than that of N + C on tailings' physical and chemical properties. Two improvers can reduce the enrichment and the stress degree of Pb and Zn on the N. oleander and increase the accumulation of Pb and Zn while promoting the growth of the N. oleander. The content of Pb and Zn showed the trend of root > stem > leaf under the two improvers, and the content of Zn was basically higher than that of Pb. To sum up, the combination of two modifiers and N. oleander has a good effect on the remediation of lead-zinc tailings, and the remediation effect of M + C was better than N + C.

Determination of cadmium in Chinese pepper and its health implications based on bioaccessibility

The contamination of cadmium (Cd) in agro-products causes major concern because of its potential dietary risks. In this study, a total of 647 pepper samples from 21 provinces in China were randomly collected according to the distribution of pepper production. Cd pollution levels in Chinses pepper and its health risks were evaluated based on bioaccessibility, which was measured by the physiologically based extraction test (PBET). The results showed that Cd concentration in all pepper ranged from 0.002 to 1.470 mg/kg, with an average of 0.222 mg/kg and a median of 0.132 mg/kg. The highest daily intake of Cd was observed in the female child group (4.037 × 10^-5 mg/kg bw/day), which accounted for 4% of the maximum daily permissible dose - 0.001 mg/kg bw/day. The target hazard quotients of Cd were all lower than 1, indicating low potential non-carcinogenic health risks to residents via the consumption of pepper. Notably, carcinogenic risk values suggested potential adverse health effects to adults, while after considering the bioaccessibility of Cd in pepper (mean of 43.07%), those values had fallen under the acceptable level (1 × 10^-4). This may indicate that dietary risk assessment of heavy metals in crops could not be conducted just based on their content; the bioaccessibility of metals is also an important factor for consideration.

Comparison of Phytoremediation Potential of Nerium indicum with Inorganic Modifier Calcium Carbonate and Organic Modifier Mushroom Residue to Lead-Zinc Tailings

At present, the application of phytoremediation technology in the ecological remediation of heavy metal tailings is receiving more and more attention. In this study, the physiological and biochemical response and tolerance mechanism of woody plant Nerium indicum to Pb and Zn under different proportions of inorganic modifier calcium carbonate (C1: 5%, C2: 10%, C3: 15%) and organic modifier mushroom residue (M1: 10%, M2: 20%, M3: 30%) was compared. The results showed that the pH value has a trend of C group > M group > CK group and organic matter has a trend of M group > CK group > C group. Phosphatase activity and catalase activity has a trend of M group > C group > CK group, but catalase was more vulnerable to the calcium carbonate concentration. Both modifiers can promote the transformation of Pb, Zn, Cu, and Cd in tailings to more stable organic bound and residual states. However, the stabilization effect of mushroom residue is better, and its stability is Pb, Zn > Cd, Cu. Both modifiers can increase the biomass of Nerium indicum and the modification effect of mushroom residue is better than calcium carbonate. Pb/Zn content and accumulation in Nerium indicum organs showed root > stem > leaf in all groups. Compared with the CK group, the enrichment coefficient of Pb/Zn in C1 and M1 groups decreased, while the translocation factor of Pb/Zn in C1 and M1 groups increased. With the increase in modifier concentration, the enrichment coefficient increases about 1.75~52.94%, but the translocation factor decreases rapidly (20.01~64.46%). Clearly, both the calcium carbonate and mushroom residue amendment could promote the growth ability of Nerium indicum in lead−zinc tailings and strengthen the phytoremediation potential.

Polymer amendment regulates cadmium migration in cadmium contaminated cotton field: Insights from genetic adaptation and phenotypic plasticity

Polymer materials have been widely used in the remediation of soil heavy metal contamination for their good performance in the absorption of metal ions. To reveal the effect of polymer amendment (PA) on the remediation of cadmium-contaminated cotton fields, the cadmium (Cd) fractions in soil, Cd concentration in cotton organs, bioconcentration factor (BCF) of Cd, translocation factor (TF) of Cd, and the antioxidant capacity and photosynthesis of functional leaves were evaluated combining with the transcriptomic and metabolomic analyses, in barrel experiments in the field at the flowering and boll-forming stage of cotton. The results showed that, cotton improved the tolerance to Cd through self-regulation in Cd-contaminated soil. The expression of oxoglutaric acid and jasmonic acid were down-regulated by the application of PA to improve the photosynthetic rate (7.71%-46.20%), chlorophyll content (17.59%-63.18%), chlorophyll fluorescence (7.66%-32.25%), and antioxidant enzyme activity (15.49%-45.50%) of functional leaves, and the down-regulation of the expression of jasmonic acid and up-regulation of the expression of stearic acid reduced the exchangeable Cd concentration in the soil, which reduced the transport of Cd from the root to the bolls (54.39%). Thereby, the balance of the genetic adaptation and phenotypic plasticity of cotton was achieved, and the cell structure of leaves was restored. This study deepens our understanding of the molecular mechanism of PA in the remediation of Cd contamination in cotton fields, and provides guidance for the remediation of heavy metal contamination in farmland soil and agricultural safety under drip irrigation.