An experiment was performed to explore the interactive impacts of zinc oxide nanoparticles (ZnO NPs) and cadmium (Cd) on growth, yield, antioxidant enzymes, Cd and zinc (Zn) concentrations in wheat (Triticum aestivum). The ZnO NPs were applied both in Cd-contaminated soil and foliar spray (in separate studies) on wheat at different intervals and plants were harvested after physiological maturity. Results depicted that ZnO NPs enhanced the growth, photosynthesis, and grain yield, whereas Cd and Zn concentrations decreased and increased respectively in wheat shoots, roots and grains. The Cd concentrations in the grains were decreased by 30–77%, and 16–78% with foliar and soil application of NPs as compared to the control, respectively. The ZnO NPs reduced the electrolyte leakage while increased SOD and POD activities in leaves of wheat. It can be concluded that ZnO NPs (levels used in the study) could effectively reduce the toxicity and concentration of Cd in wheat whereas increase the Zn concentration in wheat. Thus, ZnO NPs might be helpful in decreasing Cd and increasing Zn biofortification in cereals which might be effective to reduce the hidden hunger in humans owing the deficiency of Zn in cereals.

The accurate assessment of soil selenium (Se) bioavailability is crucial for Se biofortification in Se-deficient areas and risk assessment in selenosis areas. However, a universally accepted approach to evaluate Se bioavailability in soil is currently lacking. This research investigated Se bioavailability in six soils treated with selenite (Se(IV)) or selenate (Se(VI)) by comparing diffusive gradients in thin-films (DGT) technique and chemical extraction methods through pot experiments. A bioindicator method was used to evaluate Se concentrations in pak choi and compare the results with the Se concentration measured by other methods. Results showed that chemical extraction methods presented different extraction efficiencies for available Se over a range of soil types, and the same extraction method had various extraction efficiencies for different Se species in the same soil. DGT measured Se concentrations (CDGT−Se) for Se(VI) treatment were 2.3–34.1 times of those for Se(IV) treatment. KH2PO4–K2HPO4 and AB-DTPA extractable Se could predict the bioavailability of soil Se, but they were disturbed by soil properties. HAc extraction was unsuitable for evaluating Se bioavailability in different Se(IV)-treated soils. By contrast, DGT technique was preferable for predicting plant uptake of Se(IV) over chemical extraction methods. Although DGT technique was independent of soil properties, KH2PO4–K2HPO4 extraction provided the best fitting regression equation for Se(VI) when it was dependent on soil organic matter. Thus, KH2PO4–K2HPO4 extraction may be preferred to assess Se(VI) bioavailability in different soil types on a large scale.

Phytoremediation coupled with agro-production is considered a sustainable strategy for remediation of trace element contaminated fields without interrupting crop production. In this study hyperaccumulator Sedum alfredii was intercropped with a leguminous plant fava bean (Vicia fava) in cadmium (Cd) and lead (Pb) co-contaminated field to evaluate the effects of intercropping on growth performance and accumulations of trace elements in plants with plant growth promoting endophyte (PGPE) consortium application. The results showed, compared with monoculture, intercropping coupled with inoculation application promoted biomass as well as Cd and Pb concentrations in individual parts of both plants, thus increasing the removal efficiencies of trace elements (4.49-folds for Cd and 5.41-folds for Pb). Meanwhile, this superposition biofortification measure maintained normal yield and nutrient content, and limited the concentration of Cd and Pb within the permissible limit (<0.2 mg kg⁻¹ FW) in fava bean during the grain production. These results demonstrated a feasible technical system for phytoremediation coupled with agro-production in slightly or moderately Cd and Pb co-contaminated field, and also provided useful information for further investigation of interaction mechanisms between intercropping and PGPEs inoculation.

Selenium (Se) speciation in soil is critically important for understanding the solubility, mobility, bioavailability, and toxicity of Se in the environment. In this study, Se fractionation and chemical speciation in agricultural soils from seleniferous areas were investigated using the elaborate sequential extraction and X-ray absorption near-edge structure (XANES) spectroscopy. The speciation results quantified by XANES technique generally agreed with those obtained by sequential extraction, and the combination of both approaches can reliably characterize Se speciation in soils. Results showed that dominant organic Se (56–81%) and lesser Se(IV) (19–44%) were observed in seleniferous agricultural soils. A significant decrease in the proportion of organic Se to the total Se was found in different types of soil, i.e., paddy soil (81%) > uncultivated soil (69–73%) > upland soil (56–63%), while that of Se(IV) presented an inverse tendency. This suggests that Se speciation in agricultural soils can be significantly influenced by different cropping systems. Organic Se in seleniferous agricultural soils was probably derived from plant litter, which provides a significant insight for phytoremediation in Se-laden ecosystems and biofortification in Se-deficient areas. Furthermore, elevated organic Se in soils could result in higher Se accumulation in crops and further potential chronic Se toxicity to local residents in seleniferous areas.

Micronutrient deficiencies are prevalent health problems worldwide. The maintenance of adequate concentrations of micronutrients in maize grain is crucial for human health. We investigated the overall status and geospatial variation of micronutrients in Chinese maize grains and identified their key drivers. A field survey was conducted in four major maize production areas of China in 2017 with 980 pairs of soil and grain samples collected from famers’ fields. At a national scale, grain zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu) concentrations varied substantially, with average values of 17.4, 17.3, 4.9, and 1.5 mg kg⁻¹, respectively, suggesting a solid gap between grain Zn and Fe concentrations and the biofortification target values. Significant regional difference in the concentrations of Zn, Mn and Cu, but not Fe, were observed in grain, with much higher levels in Southwest China. The nutritional yields of Zn, Fe and Cu were lower than the energy and Mn yields, indicating an unbalanced output between energy and micronutrients in current maize production system. Grain Zn, Fe, Mn and Cu correlated negatively with maize yield in most test regions. Increased nitrogen (N) rate positively affected grain Zn and Cu, while increased phosphorus (P) rate negatively affects grain Zn and Fe. Apart from Fe, available Zn, Mn and Cu in soil exerted significant positive effects on grain Zn, Mn and Cu concentrations, respectively. Decrease in soil pH and increase in the organic matter content may increase the accumulation of Fe and Mn in grain. Grain Zn and Cu concentrations increased as available soil P decreased. Of the factors considered in this study, grain yield, N and P rates, soil pH and organic matter were the main factors that affect grain micronutrient status and should be more extensively considered in the production and nutritional quality of maize grain.

Delay sowing of wheat is a common problem in Punjab that exacerbates serious yield loss. To reduce yield loss and improve yield, different combinations of foliar-applied bioregulator and micronutrients, control (CK), zinc (Zn), boron (B), thiourea (TU), Zn + B (ZnB), Zn + TU (ZnTU), B + TU (BTU), Zn + B + TU (ZnBTU) were applied at booting and grain filling stages in delayed sown wheat in 2017–18 and 2018–19. The results showed that ZnBTU treatment significantly increased leaf area index by 25.06% and 23.21%, spike length by 15.11% and 19.65% in 2017 and 2018, respectively, compared to CK. The ZnBTU treatment also increased 1000-grain weight by 21.96% and 22.01% in 2017 and 2018, respectively, compared to CK. Similarly, higher Zn, B and N contents in straw and grain were recoded for ZnBTU treatment which was statistically similar to ZnB and ZnTU treatments. Overall, ZnBTU treatment also increased the photosynthetic rate, transpiration rate, stomatal conductance by 46.67%, 26.03%, 76.25% and decreased internal CO₂ by 28.18%, compared to CK, respectively. Moreover, ZnBTU also recorded the highest grain yield in 2017–18 (25.05%) and 2018–19 (28.49%) than CK. In conclusion, foliar application of ZnBTU at the booting and grain filling stages of delayed sown wheat could be a promising strategy to increase grain yield.

In plants, excess selenium causes general toxic symptoms. However, salicylic acid plays an important role in alleviating toxic effects of various stresses. This study aimed to clarify the role of exogenous foliar salicylic acid on alleviating selenium toxicity of pak choi exposed to moderately and highly Se-excessive soils (4 mg·kg⁻¹ Se and 10 mg·kg⁻¹ Se, respectively). The results showed that Se stress caused severe lipid peroxidation, desynchronization of the antioxidant enzymatic system, and significant decreases in the measures of photosynthetic activity and shoot biomass. Under Se stress conditions, exogenous foliar salicylic acid significantly increased measures of photosynthetic activity and shoot biomass, increased catalase activity, and decreased measures of oxidative stress. Moreover, exogenous salicylic acid significantly enhanced Se accumulation in shoots under Se stress conditions. We demonstrate here that foliar spraying with salicylic acid is an effective measure to alleviate the adverse effects of Se stress and enhance Se accumulation for optimizing crop Se biofortification in Se-excessive soil.

Agronomic selenium (Se) biofortification of grain crops is considered the best method for increasing human Se intake, which may help people alleviate Se-deficiency. To investigate the efficiency of agronomic Se biofortification of oat, four Se fertilizer application treatments were tested: topsoil (T), foliar (S), the combination of T and S (TS), and control without Se application (CK). Compared with CK, TS significantly increased the 1000-grain weight, grain yield, Se contents in all parts of oats, contents of soil available N, K, and organic matter by 18%, 8.70%, 19.7–60.2%, 6.00%, 8.02%, and 17.95%, respectively. Leaves, roots, and ears had the highest conversion rate of exogenous Se in S (644.63%), T (416.00%), and TS (273.20%), respectively. TS also increased the activities of soil urease, alkaline phosphatase, and sucrose and the diversity of soil bacterial communities. TS and T increased the relative abundance of bacteria involved in the decomposition of organic matter, such as Actinobacteria, Gemmatimonadetes, Chloroflexi, and Bacteroidetes positively correlated with soil nutrients and enzyme activities, and reduced Proteobacteria and Firmicutes negatively correlated with them, Granulicella, Bacillus, Raoultella, Lactococcus, Klebsiella, and Pseudomonas. Furthermore, TS significantly increased the relative abundance of Planctomycetes, Chlorobi, Nitrospinae, Nitrospirae, Aciditeromonas, Gemmatimonas, Geobacter, and Thiobacter. T significantly increased the abundance of Lysobacter, Holophaga, Candidatus-Koribacter, Povalibacter, and Pyrinomonas. S did not significantly change the bacterial communities. Thus, a combined foliar and soil Se fertilizer proved conducive for achieving higher yield, grain Se content, and improving Se transport, the diversity of rhizosphere bacterial community, and bacterial functions in oats.

The biosphere is polluted with metals due to burning of fossil fuels, pesticides, fertilizers, and mining. The metals interfere with soil conservations such as contaminating aqueous waste streams and groundwater, and the evidence of this has been recorded since 1900. Heavy metals also impact human health; therefore, the emancipation of the environment from these environmental pollutants is critical. Traditionally, techniques to remove these metals include soil washing, removal, and excavation. Metal-accumulating plants could be utilized to remove these metal pollutants which would be an alternative option that would simultaneously benefit commercially and at the same time clean the environment from these pollutants. Commercial application of pollutant metals includes biofortification, phytomining, phytoremediation, and intercropping. This review discusses about the metal-accumulating plants, mechanism of metal accumulation, enhancement of metal accumulation, potential commercial applications, research trends, and research progress to enhance the metal accumulation, benefits, and limitations of metal accumulators. The review identified that the metal accumulator plants only survive in low or medium polluted environments with heavy metals. Also, more research is required about metal accumulators in terms of genetics, breeding potential, agronomics, and the disease spectrum. Moreover, metal accumulators’ ability to uptake metals need to be optimized by enhancing metal transportation, transformation, tolerance to toxicity, and volatilization in the plant. This review would benefit the industries and environment management authorities as it provides up-to-date research information about the metal accumulators, limitation of the technology, and what could be done to improve the metal enhancement in the future.

Selenium (Se) is an essential micronutrient for humans and livestock. Its toxicity is prominently observed in soils naturally rich in selenium and its deficiency disorders in low selenium areas. In the present investigation, several fungi were isolated from seleniferous agricultural soils (~ 6 mg Se kg⁻¹ of soil) and tested for selenium tolerance, uptake, and plant growth promotion. Two Se-tolerant fungal isolates (SeF5 and SeF12) were selected and tested for their efficacy to improve plant growth and Se uptake in maize plants grown in seleniferous soils. These fungi were identified as Fusarium equiseti (SeF5) and Pseudopestalotiopsis theae (SeF12) based on their morphology and internal transcribed spacer (ITS) sequence analysis. Inoculation of maize plants with SeF5 and SeF12 significantly increased the growth compared to control. SeF5 inoculation increased the accumulation of Se in the shoots, whereas SeF12 showed greater selenium accumulation in the roots. The present study results suggest that maize crops and Se-tolerant fungi enhance Se accumulating ability in plants, facilitating the potential use for biofortification.