Maria Manzoor

Cadmium (Cd) contamination in soil poses significant risks to environmental and crop safety. One of the most important parameters controlling Cd uptake by plants from soil is pH. The role of soil pH in regulating Cd availability and its uptake by plants has been studied; however, no study has yet compared how pH changes in the rhizosphere and bulk soil differentially influence these processes. This study examined how nitrification inhibitor (3,4-Dimethylpyrazole phosphate (DMPP)) and lime affect Cd availability and concentration in wheat via modulating pH and calcium (Ca) availability in rhizosphere and bulk soil. Wheat was grown in acidic sandy soil under three lime application rates and two DMPP levels to investigate Cd accumulation. Our results indicated that DMPP application was associated with decreased rhizosphere pH, exchangeable Ca and Cd accumulation in wheat shoots. The impact of lime on shoot Cd varied depending on the presence of DMPP. Liming generally increased soil pH and exchangeable Ca and was associated with decreased plant-available Cd (CaCl₂-extractable Cd) in both bulk soil and the rhizosphere. In the absence of DMPP, liming was associated with a greater increase in exchangeable Ca in the rhizosphere and reduction in plant-available Cd (CaCl₂-extractable Cd) in the rhizosphere and bulk soil. Despite the decline in soil Cd availability, these changes were associated with higher Cd concentration and content in wheat shoots. In contrast, under DMPP application, liming decreased shoot Cd concentration but did not affect shoot Cd content, suggesting that DMPP may influence the response of shoot Cd concentration to liming. The results provide useful insights into Cd management in agricultural systems and may contribute to strategies for reducing Cd-related risks in crop production.

Cadmium accumulation in wheat as a daily food, even in low concentrations, is a serious threat to human health. Previous studies have reported conflicting results on the impact of calcium treatments on cadmium uptake and translocation in plants due to the complex soil conditions. Our hydroponic study offers clearer insights into how specific calcium treatment parameters influence cadmium uptake and translocation in wheat. The hydroponic medium was contaminated by cadmium (CdCl₂) and the following treatments were applied: CaCO₃, CaSO₄, CaCl₂, CaCO₃ + CaSO₄, CaCO₃ + CaCl₂, and CaSO₄ + CaCl₂. After harvesting, the wheat was analyzed for Cd²⁺ uptake characteristics including translocation factor, bioconcentration factor, and uptake. Furthermore, physiological growth parameters and plant nutrients were also determined. Applying CaCO₃ significantly decreased wheat Cd²⁺ concentration by about three times in CaCO₃ and two times in CaCO₃ + CaSO₄ and CaCO₃ + CaCl₂ treatments than in Cd-control. This study clearly elucidates that pH and CO₃²⁻ were crucial in reducing Cd²⁺ concentration in wheat. SO₄²⁻, Cl⁻, and Ca²⁺ showed no effect on Cd²⁺ concentration. Ca²⁺ only reduced the translocation factor (TF) of Cd²⁺ in plants. CaCO₃ also declined cadmium interference in the Mg²⁺, Mn²⁺, and Cu²⁺ uptake. Therefore, this study provides novel insight into the pure effects of calcium treatments on controlling cadmium contamination in plants, independent of soil effect.

Cadmium (Cd), being a highly toxic heavy metal, significantly impacts plant growth and development by altering nutrient uptake and causing oxidative and structural damage, resulting in reduced yield. To combat Cd toxicity and accumulation in wheat, it was hypothesized that co-application of Selenium (Se) and Silicon (Si) can reduce the adverse effect of Cd and regulate Cd resistance while improving Se fortification in wheat. Therefore, this study evaluated the comparative effect of Se and Si on the growth and antioxidant defense systems of wheat plants grown in a hydroponic setup. Briefly, the plants were acclimatized to the hydroponic solution for 1 week and then exposed to 10 µmol Cd. Afterwards, the treatments, including 0.2 mmol Si and 1.5 µmol Se, were applied as a root and foliar application, respectively. Plants supplemented with both Se and Si showed improved biomass and other physiological growth attributes, and this response was associated with improved activity/contents of antioxidants, including glutathione (GSH) content, glutathione reductase (GR), ascorbate peroxidase (APX), and catalase (CAT), with related lowering of hydrogen peroxide, malondialdehyde content, and structural damages. Moreover, by Se + Si supplementation, a decrease in total S levels in plant tissues was observed, whereas an increase in total protein concentration and GSH indicated a different and novel mechanism of Cd tolerance and S homeostasis in the plant. It was observed that Si was more involved in significantly reducing Cd translocation by stabilizing Cd in the root and reducing its content in the soluble fraction in both the root and shoot. Whereas Se was found to play the main role in reducing the oxidative damage caused by Cd, and the effect was more profound in the shoot. In addition, this study also observed a positive correlation between Si and Se for relative uptake, which had not been reported earlier. Our findings show that the Se and Si doses together benefit growth regulation and nutrient uptake; additionally, their combinations support the Cd resistance mechanism in wheat through upregulation of the antioxidant system and control of Cd translocation and subcellular distribution, ultimately contributing to the nutritional quality of wheat produced. Thus, it is concluded that the co-application of Se and Si has improved the nutritional quality while reducing the Cd risk in wheat and therefore needs to be employed as a potential strategy to ensure food safety in a Cd-contaminated environment.

Lead (Pb) is well known for the containment of soil surfaces. In the last few decades, phytoremediation has been the most ideal technology to extract Pb from soil, involving numerous chemical reactions and cost analysis. The aim of this study is to model and to optimize Pb extraction from the contaminated soil via Pelargonium hortorum by comparing two modeling approaches: response surface methodology (RSM) and artificial neural networks (ANNs) with the genetic algorithm (GA). To determine the significance of the proposed solution, in vitro essays were performed to check the Pb tolerance of bacterial strains (NCCP 1844, 1848, 1857, and 1862), followed by the co-application of bacteria and citric acid on a Pb hyperaccumulator (Pelargonium hortorum L.) on Murashige and Skoog (MS) agar medium. Afterwards, a pot culture experiment was performed to optimize Pb extraction competency from Pb-spiked (0 mg kg⁻¹, 500 mg kg⁻¹, 1000 mg kg⁻¹, and 1500 mg kg⁻¹) soil by Pelargonium hortorum L., to which citric acid (5 and 10 mmol L⁻¹) and Microbacterium paraoxydance (1 and 1.5 OD) were applied. Plants were harvested at 30, 60, and 90 day intervals, and they were analyzed for dry biomass and Pb uptake characteristics. The maximum Pb extraction efficiency of 86.0% was achieved with 500 mg kg⁻¹ soil Pb for 60 days. Furthermore, RSM, based on the Box–Behnken design (BBD) and the ANN-based Levenberg–Marquardt Algorithm (LMA), were applied to model Pb extraction from the soil. The significance of the predicted values from RSM and LMA were close to 36.0% and 86.05%, respectively, compared to the laboratory values. The comprehensive evaluation of these findings encouraged the accuracy, reliability, and efficiency of the ANN for the optimization process. Therefore, experimental results showed that ANN is an accurate technique to optimize an integrated phytoremediation system for sustainable Pb removal, besides being environmentally friendly and potentially cost-effective.