Foliar Application of Low Concentrations of Titanium Dioxide and Zinc Oxide Nanoparticles to the Common Sunflower under Field Conditions

Green synthesis and characterization of Fe2O3, ZnO and TiO2 nanoparticles and searching for their potential use as biofertilizer on sunflower

Nanoparticles, thanks to their superior properties such as large surface area and high reactivity, can be an alternative to traditional fertilizers for improving nutrient uptake. Furthermore, considering that chemical and physical synthesis methods require high energy consumption and cause environmental pollution, plant-mediated green synthesis of NPs has attracted great attention since it provides eco-friendly, biocompatible, and inexpensive solutions. In this present study, plant mediated green synthesis of Iron Oxide (Fe2O3), Zinc Oxide (ZnO) and Titanium Dioxide (TiO2) nanoparticles by using Laurus nobilis leaves (bay leaves) were carried out and their structural properties were characterized by UV visible spectra, Dynamic Light Scattering (DLS), Fourier Transform Infrared (FTIR), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). UV spectrum and FTIR analysis exhibited characteristic peaks indicating the presence of the desired NPs, while DLS analysis and TEM images confirmed that synthesized particles are in nano-scale. The potential of nanoparticles as biofertilizer in agricultural uses were assessed by investigating their effects on sunflower growth in hydroponic system. TEM images of the NP applied plant tissues proved the uptake and translocation of NPs from root to leaf. Furthermore, Fe2O3, ZnO and TiO2 NP applications on sunflower up to 5 ppm generally improved physiological growth parameters such as root length, fresh weight and leaf surface area while 20 ppm of Fe2O3 and ZnO NPs application cause a significant decrease.

Graphical abstract

Nanoparticle-plant interactions: Physico-chemical characteristics, application strategies, and transmission electron microscopy-based ultrastructural insights, with a focus on stereological research

Ensuring global food security is pressing among challenges like population growth, climate change, soil degradation, and diminishing resources. Meeting the rising food demand while reducing agriculture's environmental impact requires innovative solutions. Nanotechnology, with its potential to revolutionize agriculture, offers novel approaches to these challenges. However, potential risks and regulatory aspects of nanoparticle (NP) utilization in agriculture must be considered to maximize their benefits for human health and the environment. Understanding NP-plant cell interactions is crucial for assessing risks of NP exposure and developing strategies to control NP uptake by treated plants. Insights into NP uptake mechanisms, distribution patterns, subcellular accumulation, and induced alterations in cellular architecture can be effectively drawn using transmission electron microscopy (TEM). TEM allows direct visualization of NPs within plant tissues/cells and their influence on organelles and subcellular structures at high resolution. Moreover, integrating TEM with stereological principles, which has not been previously utilized in NP-plant cell interaction assessments, provides a novel and quantitative framework to assess these interactions. Design-based stereology enhances TEM capability by enabling precise and unbiased quantification of three-dimensional structures from two-dimensional images. This combined approach offers comprehensive data on NP distribution, accumulation, and effects on cellular morphology, providing deeper insights into NP impact on plant physiology and health. This report highlights the efficient use of TEM, enhanced by stereology, in investigating diverse NP-plant tissue/cell interactions. This methodology facilitates detailed visualization of NPs and offers robust quantitative analysis, advancing our understanding of NP behavior in plant systems and their potential implications for agricultural sustainability.

Nanoparticle-mediated defense priming: A review of strategies for enhancing plant resilience against biotic and abiotic stresses

Nanotechnology has emerged as a promising field with the potential to revolutionize agriculture, particularly in enhancing plant defense mechanisms. Nanoparticles (NPs) are instrumental in plant defense priming, where plants are pre-exposed to controlled levels of stress to heighten their alertness and responsiveness to subsequent stressors. This process improves overall plant performance by enabling quicker and more effective responses to secondary stimuli. This review explores the application of NPs as priming agents, utilizing their unique physicochemical properties to bolster plants' innate defense mechanisms. It discusses key findings in NP-based plant defense priming, including various NP types such as metallic, metal oxide, and carbon-based NPs. The review also investigates the intricate mechanisms by which NPs interact with plants, including uptake, translocation, and their effects on plant physiology, morphology, and molecular processes. Additionally, the review examines how NPs can enhance plant responses to a range of stressors, from pathogen attacks and herbivore infestations to environmental stresses. It also discusses NPs' ability to improve plants' tolerance to abiotic stresses like drought, salinity, and heavy metals. Safety and regulatory aspects of NP use in agriculture are thoroughly addressed, emphasizing responsible and ethical deployment for environmental and human health safety. By harnessing the potential of NPs, this approach shows promise in reducing crop losses, increasing yields, and enhancing global food security while minimizing the environmental impact of traditional agricultural practices. The review concludes by emphasizing the importance of ongoing research to optimize NP formulations, dosages, and delivery methods for practical application in diverse agricultural settings.

Enhancing Maize Yield and Quality with Metal-Based Nanoparticles without Translocation Risks: A Brief Field Study

Our previous studies have shown physiological and yield intensification of selected crops with the application of nanoparticles (NPs). However, the impact on the quantitative, qualitative, and yield parameters of maize (Zea mays L.) in field conditions remains highly debated. This study aimed to evaluate the effects of zinc oxide (ZnO-NPs), gold NPs anchored to meso-biosilica (Au-NP-bioSi), and titanium dioxide (TiO2-NPs) as biological stimulants under field conditions during the vegetation season of 2021 in the Central European region. The study assessed the effects on the number of plants, yield, yield components, and nutritional quality, including mineral nutrients, starch, and crude protein levels. The potential translocation of these chemically-physically stable NPs, which could pose a hazard, was also investigated. The results indicate that Au-NP-bioSi and ZnO-NPs-treatments were the most beneficial for yield and yield components at a statistically significant level. Mineral nutrient outcomes were varied, with the NP-free variant performing the best for phosphorus-levels, while Au-NP-bioSi and ZnO-NPs were optimal for crude protein. Starch content was comparable across the TiO2-NPs, Au-NP-bioSi, and control variants. Importantly, we observed no hazardous translocation of NPs or negative impacts on maize grain quality. This supports the hypothesis that NPs can serve as an effective tool for precise and sustainable agriculture.

An assessment of nanotechnology-based interventions for cleaning up toxic heavy metal/metalloid-contaminated agroecosystems: Potentials and issues

Heavy metals (HMs) are among the most dangerous environmental variables for a variety of life forms, including crops. Accumulation of HMs in consumables and their subsequent transmission to the food web are serious concerns for scientific communities and policy makers. The function of essential plant cellular macromolecules is substantially hampered by HMs, which eventually have a detrimental effect on agricultural yield. Among these HMs, three were considered, i.e., arsenic, cadmium, and chromium, in this review, from agro-ecosystem perspective. Compared with conventional plant growth regulators, the use of nanoparticles (NPs) is a relatively recent, successful, and promising method among the many methods employed to address or alleviate the toxicity of HMs. The ability of NPs to reduce HM mobility in soil, reduce HM availability, enhance the ability of the apoplastic barrier to prevent HM translocation inside the plant, strengthen the plant's antioxidant system by significantly enhancing the activities of many enzymatic and nonenzymatic antioxidants, and increase the generation of specialized metabolites together support the effectiveness of NPs as stress relievers. In this review article, to assess the efficacy of various NP types in ameliorating HM toxicity in plants, we adopted a 'fusion approach', in which a machine learning-based analysis was used to systematically highlight current research trends based on which an extensive literature survey is planned. A holistic assessment of HMs and NMs was subsequently carried out to highlight the future course of action(s).

Tapioca-starch-based bionanocomposites with fructose and titanium dioxide for food packaging and fertilization applications

Bionanocomposites offer a promising solution to the plastic waste crisis. Although tapioca starch shows potential as a bioplastic material, it is characterized by low mechanical properties, poor thermal stability, and high water absorption owing to its hydrophilic nature. To increase the flexibility of the material and reduce the transmission rate of oxygen and water vapor, additives such as fructose and titanium dioxide (TiO2) can be incorporated into the material. TiO2 nanoparticles are commonly utilized in agriculture to enhance nutrient release and promote plant growth. In this study, X-ray diffraction analysis revealed that TiO2 reduced crystal size while increasing the crystallinity of bionanocomposites. Fourier-transform infrared spectroscopy analysis revealed an absorption peak at 3397 cm-1, indicating hydrogen bonding between TiO2 and starch-OH groups, and a peak at 773 cm-1, indicating an increase in the intensity of Ti-O-Ti stretching vibrations with the incorporation of TiO2. Water absorption rate results confirmed that TiO2 addition enhanced bionanocomposite resistance to water vapor and moisture, evidenced by increased tensile strength from 0.11 to 0.49 MPa and Young's modulus from 2.48 to 5.26 MPa, as well as decreased elongation at break from 21.46 % to 2.36 % in bionanocomposites with TiO2. Furthermore, with TiO2 addition, the biodegradation rate of the bionanocomposites decreased, which is beneficial for enhancing plant nutrient content.

Advancement of metal oxide nanomaterials on agri-food fronts

The application of metal oxide nanomaterials (MOx NMs) in the agrifood industry offers innovative solutions that can facilitate a paradigm shift in a sector that is currently facing challenges in meeting the growing requirements for food production, while safeguarding the environment from the impacts of current agriculture practices. This review comprehensively illustrates recent advancements and applications of MOx for sustainable practices in the food and agricultural industries and environmental preservation. Relevant published data point out that MOx NMs can be tailored for specific properties, enabling advanced design concepts with improved features for various applications in the agrifood industry. Applications include nano-agrochemical formulation, control of food quality through nanosensors, and smart food packaging. Furthermore, recent research suggests MOx's vital role in addressing environmental challenges by removing toxic elements from contaminated soil and water. This mitigates the environmental effects of widespread agrichemical use and creates a more favorable environment for plant growth. The review also discusses potential barriers, particularly regarding MOx toxicity and risk evaluation. Fundamental concerns about possible adverse effects on human health and the environment must be addressed to establish an appropriate regulatory framework for nano metal oxide-based food and agricultural products.

Green-synthesized zinc oxide nanoparticles by Enterobacter sp.: unveiling characterization, antimicrobial potency, and alleviation of copper stress in Vicia faba (L.) plants

BACKGROUND

The biosynthesis of zinc oxide nanoparticles (ZnO NPs) using Enterobacter sp. and the evaluation of their antimicrobial and copper stress (Cu+ 2)-reducing capabilities in Vicia faba (L.) plants. The green-synthesized ZnO NPs were validated using X-ray powder diffraction (XRD); Fourier transformed infrared (FTIR), Ultraviolet-Visible spectroscopy (UV-Vis), Transmission electron microscope (TEM) and scanning electron microscopy (SEM) techniques. ZnO NPs could serve as an improved bactericidal agent for various biological applications. as well as these nanoparticles used in alleviating the hazardous effects of copper stress on the morphological and physiological traits of 21-day-old Vicia faba (L.) plants.

RESULTS

The results revealed that different concentrations of ZnO NPs (250, 500, or 1000 mg L-1) significantly alleviated the toxic effects of copper stress (100 mM CuSO4) and increased the growth parameters, photosynthetic efficiency (Fv/Fm), and pigments (Chlorophyll a and b) contents in Cu-stressed Vicia faba (L.) seedlings. Furthermore, applying high concentration of ZnO NPs (1000 mg L-1) was the best dose in maintaining the levels of antioxidant enzymes (CAT, SOD, and POX), total soluble carbohydrates, total soluble proteins, phenolic and flavonoid in all Cu-stressed Vicia faba (L.) seedlings. Additionally, contents of Malondialdehyde (MDA) and hydrogen peroxide (H2O2) were significantly suppressed in response to high concentrations of ZnO NPs (1000 mg L-1) in all Cu-stressed Vicia faba (L.) seedlings. Also, it demonstrates strong antibacterial action (0.9 mg/ml) against various pathogenic microorganisms.

CONCLUSIONS

The ZnO NPs produced in this study demonstrated the potential to enhance plant detoxification and tolerance mechanisms, enabling plants to better cope with environmental stress. Furthermore, these nanoparticles could serve as an improved bactericidal agent for various biological applications.

Recent Trends in Foliar Nanofertilizers: A Review

It is estimated that 40-70%, 80-90% and 50-90% of the conventional macronutrients N, P and K applied to the soil are lost, respectively, resulting in considerable loss of resources. Compared to conventional fertilizers, nanofertilizers have the advantages of controlled release, high nutrient utilization, low cost and relatively low environmental pollution due to their small size (1-100 nm) and high specific surface area. The application of nanofertilizers is an up-and-coming field of agricultural research and is an attractive and economical substitute for common fertilizers which can boost global food productivity sustainably. Foliar fertilization is a popular way to satisfy the needs of higher plants. Because of its small application dose, faster nutrient uptake than soil application and relatively less environmental pollution, foliar fertilization is more popular among plants. It can be seen that nanofertilizers and foliar fertilization are the hotspots of attention at present and that current research on the foliar application of nanofertilizers is not as extensive as that on soil application. Based on this background, this paper provides an overview of various applications of foliar spraying of nanofertilizers in agriculture, including applications in improving crop yield and quality as well as mitigating heavy metal stress, salt stress and drought stress.

Functional impacts of polyaniline in composite matrix of photocatalysts: an instrumental overview

The challenges associated with photocatalysts including their agglomeration, electron-hole recombination and limited optoelectronic reactivity to visible light during the photocatalysis of dye-laden effluent make it necessary to fabricate versatile polymeric composite photocatalysts, and in this case the incredibly reactive conducting polyaniline can be employed. The selection of polyaniline among the conducting polymers is based on its proficient functional impacts in composite blends and proficient synergism with other nanomaterials, especially semiconductor catalysts, resulting in a high photocatalytic performance for the degradation of dyes. However, the impacts of PANI in the composite matrix, which result in the desired photocatalytic activities, can only be assessed using multiple characterization techniques, involving both microscopic and spectroscopic assessment. The characterization results play a significant role in the detection of possible points of agglomeration, surface tunability and improved reactivity during the fabrication of composites, which are necessary to improve their performance in the photocatalysis of dyes. Accordingly, studies revealed the functional impacts of polyaniline in composites including morphological transformation, improved surface functionality, reduction in agglomeration and lowered bandgap potential employing different characterization techniques. In this review, we present the most proficient fabrication techniques based on the in situ approach to achieve improved functional and reactive features and efficiencies of 93, 95, 96, 98.6 and 99% for composites in dye photocatalysis.

Agronomic Investigation of Spray Dispersion of Metal-Based Nanoparticles on Sunflowers in Real-World Environments

In environmental and agronomic settings, even minor imbalances can trigger a range of unpredicted responses. Despite the widespread use of metal-based nanoparticles (NPs) and new bio-nanofertilizers, their impact on crop production is absent in the literature. Therefore, our research is focused on the agronomic effect of spray application of gold nanoparticles anchored to SiO₂ mesoporous silica (AuSi-NPs), zinc oxide nanoparticles (ZnO-NPs), and iron oxide nanoparticles (Fe₃O₄-NPs) on sunflowers under real-world environments. Our findings revealed that the biosynthetically prepared AuSi-NPs and ZnO-NPs were highly effective in enhancing sunflower seasonal physiology, e.g., the value of the NDVI index increased from 0.012 to 0.025 after AuSi-NPs application. The distribution of leaf trichomes improved and the grain yield increased from 2.47 t ha^-1 to 3.29 t ha^-1 after ZnO-NPs application. AuSi-NPs treatment resulted in a higher content of essential linoleic acid (54.37%) when compared to the NPs-free control (51.57%), which had a higher determined oleic acid. No NPs or residual translocated metals were detected in the fully ripe sunflower seeds, except for slightly higher silica content after the AuSi-NPs treatment. Additionally, AuSi-NPs and NPs-free control showed wide insect biodiversity while ZnO-NPs treatment had the lowest value of phosphorus as anti-nutrient. Contradictory but insignificant effect on physiology, yield, and insect biodiversity was observed in Fe₃O₄-NPs treatment. Therefore, further studies are needed to fully understand the long-term environmental and agricultural sustainability of NPs applications.

Nanoparticulate Silica Internalization and Its Effect on the Growth and Yield of Groundnut (Arachis hypogaea L.)

In recent years, foliar applications of nanoparticles are increasingly being employed in agricultural fields as fertilizers to enhance crop yields. However, limited studies are available on the foliar uptake of nanoscale nutrients and their interaction with plants. In this study, we reported the effects of foliar spray with varied concentrations of nanoscale silica (N-SiO₂) and bulk tetraethyl orthosilicate (TEOS at 2000 ppm) on the growth and yield of groundnut. Nanosilica was prepared by a sol-gel method and characterized by transmission electron microscopy, dynamic light scattering, and X-ray diffraction. The size and zeta potential of N-SiO₂ were found to be 28.7 nm and 32 mV, respectively. The plant height, number of branches, total dry weight, SPAD chlorophyll meter reading, photosynthetic rate, water use efficiency, number of nodules, and ascorbic acid content were increased significantly with the N-SiO₂ foliar application at 400 ppm over control. The number of filled pods increased significantly by 38.78 and 58.60% with N-SiO₂ at 400 ppm application over TEOS and control, respectively. The pod yield per plant in N-SiO₂ at 400 ppm increased by 25.52 and 31.7% higher over TEOS and control, respectively. Antioxidant enzyme activities enhanced significantly in N-SiO₂ at 200 and 400 ppm over control, indicating a stimulatory effect on the plant growth. In addition, confocal microscopy revealed that fluorescein isothiocyanate (FITC)-N-SiO₂ entered through stomata and then transported to vascular bundles via apoplastic movement. Our study for the first time demonstrated that N-SiO₂ can significantly modulate multiple complex traits in groundnut through an eco-friendly and sustainable approach.

Phytochemical and physiological reactions of feverfew (Tanacetum parthenium (L.) Schultz Bip) to TiO2 nanoparticles

Nanomaterials can be used as elicitors for improving the biosynthesis of secondary metabolites in medicinal plants. The present study was conducted to assay the titanium dioxide-nanoparticles (TiO₂-NPs) effects on feverfew (Tanacetum parthenium) as an anti-cancer plant. The study showed that TiO₂-NPs application increased the amounts of the main compounds and oxygenated monoterpene in essential oils, thereby causing an improvement in the quantity and quality of the essential oils compared to control. The highest effect was related to 1500 ppm TiO₂-NPs concentration. Regarding parthenolide, TiO₂-NPs had no positive effect on parthenolide content and the highest content was observed in control. Increasing the concentrations over 1500 ppm resulted in a decrease in chlorophyll content, capitule diameter, flower yield, and harvest index compared to other concentrations and control. Additionally, the results indicated that TiO₂-NPs foliar spray reduced flower number, biological yield, fresh weight, and dry weights compared with untreated plants. The increase in quality and content of essential oil and lack of increase in parthenolide content, and reproductive and vegetative characteristics showed that TiO₂-NPs mainly affected the content and composition of essential oil. Totally, the application of TiO2-NPs in terms of positive effect on the yield and metabolites (without damaging biological effects) can be recommended and followed up to the concentration of 1000 ppm. Overall, the results indicated that improving the synthesis of valuable medicinal metabolites using TiO₂-NPs has promising results depending on the type of species, concentration used and target metabolites.

The behavior, transport, and positive regulation mechanism of ZnO nanoparticles in a plant-soil-microbe environment

ZnO nanoparticles (ZnO NPs) have been widely used in several fields, and they have the potential to be a novel fertilizer to promote plant growth. For the effective use of ZnO NPs, it is necessary to understand their influence mechanisms and key interactions with the soil physical and biological environment. In this review, we summarize the fate and transport of ZnO NPs applied via soil treatment or foliar spray in plant-soil systems and discuss their positive regulation mechanisms in plants and microbes. The latest research shows that the formation, bioavailability, and location of ZnO NPs experience complicated changes during the transport in soil-plant systems and that this depends on many factors. ZnO NPs can improve plant photosynthesis, nutrient element uptake, enzyme activity, and the related gene expression as well as modulate carbon/nitrogen metabolism, secondary metabolites, and the antioxidant systems in plants. Several microbial groups related to plant growth, disease biocontrol, and nutrient cycling in soil can be altered with ZnO NP treatment. In this work, we present a systematic comparison between ZnO NP fertilizer and conventional zinc salt fertilizer. We also fill several knowledge gaps in current studies with the hope of providing guidance for future research.

Mycosynthesis of Metal-Containing Nanoparticles-Fungal Metal Resistance and Mechanisms of Synthesis

In the 21st century, nanomaterials play an increasingly important role in our lives with applications in many sectors, including agriculture, biomedicine, and biosensors. Over the last two decades, extensive research has been conducted to find ways to synthesise nanoparticles (NPs) via mediation with fungi or fungal extracts. Mycosynthesis can potentially be an energy-efficient, highly adjustable, environmentally benign alternative to conventional physico-chemical procedures. This review investigates the role of metal toxicity in fungi on cell growth and biochemical levels, and how their strategies of resistance, i.e., metal chelation, biomineral formation, biosorption, bioaccumulation, compartmentalisation, and efflux of metals from cells, contribute to the synthesis of metal-containing NPs used in different applications, e.g., biomedical, antimicrobial, catalytic, biosensing, and precision agriculture. The role of different synthesis conditions, including that of fungal biomolecules serving as nucleation centres or templates for NP synthesis, reducing agents, or capping agents in the synthesis process, is also discussed. The authors believe that future studies need to focus on the mechanism of NP synthesis, as well as on the influence of such conditions as pH, temperature, biomass, the concentration of the precursors, and volume of the fungal extracts on the efficiency of the mycosynthesis of NPs.

A review of the influence of nanoparticles on the physiological and biochemical attributes of plants with a focus on the absorption and translocation of toxic trace elements

Trace elements (TEs) from various natural and anthropogenic activities contaminate the agricultural water and soil environments. The use of nanoparticles (NPs) as nano-fertilizers or nano-pesticides is gaining popularity worldwide. The NPs-mediated fertilizers encourage the balanced availability of essential nutrients to plants compared to traditional fertilizers, especially in the presence of excessive amounts of TEs. Moreover, NPs could reduce and/or restrict the bioavailability of TEs to plants due to their high sorption ability. In this review, we summarize the potential influence of NPs on plant physiological attributes, mineral absorption, and TEs sorption, accumulation, and translocation. It also unveils the NPs-mediated TE scavenging-mechanisms at plant and soil interface. NPs immobilized TEs in soil solution effectively by altering the speciation of TEs and modifying the physiological, biochemical, and biological properties of soil. In plants, NPs inhibit the transfer of TEs from roots to shoots by inducing structural modifications, altering gene transcription, and strengthening antioxidant defense mechanisms. On the other hand, the mechanisms underpinning NPs-mediated TEs absorption and cytotoxicity mitigation differ depending on the NPs type, distribution strategy, duration of NP exposure, and plants (e.g., types, varieties, and growth rate). The review highlights that NPs may bring new possibilities for resolving the issue of TE cytotoxicity in crops, which may also assist in reducing the threats to the human dietary system. Although the potential ability of NPs in decontaminating soils is just beginning to be understood, further research is needed to uncover the sub-cellular-based mechanisms of NPs-induced TE scavenging in soils and absorption in plants.

Interaction of the Nanoparticles and Plants in Selective Growth Stages—Usual Effects and Resulting Impact on Usage Perspectives

Nanotechnologies have received tremendous attention since their discovery. The current studies show a high application potential of nanoparticles for plant treatments, where the general properties of nanoparticles such as their lower concentrations for an appropriate effects, the gradual release of nanoparticle-based nutrients or their antimicrobial effect are especially useful. The presented review, after the general introduction, analyzes the mechanisms that are described so far in the uptake and movement of nanoparticles in plants. The following part evaluates the available literature on the application of nanoparticles in the selective growth stage, namely, it compares the observed effect that they have when they are applied to seeds (nanopriming), to seedlings or adult plants. Based on the research that has been carried out, it is evident that the most common beneficial effects of nanopriming are the improved parameters for seed germination, the reduced contamination by plant pathogens and the higher stress tolerance that they generate. In the case of plant treatments, the most common applications are for the purpose of generating protection against plant pathogens, but better growth and better tolerance to stresses are also frequently observed. Hypotheses explaining these observed effects were also mapped, where, e.g., the influence that they have on photosynthesis parameters is described as a frequent growth-improving factor. From the consortium of the used nanoparticles, those that were most frequently applied included the principal components that were derived from zinc, iron, copper and silver. This observation implies that the beneficial effect that nanoparticles have is not necessarily based on the nutritional supply that comes from the used metal ions, as they can induce these beneficial physiological changes in the treated cells by other means. Finally, a critical evaluation of the strengths and weaknesses of the wider use of nanoparticles in practice is presented.

Foliar use of TiO2-nanoparticles for okra (Abelmoschus esculentus L. Moench) cultivation on sewage sludge-amended soils: biochemical response and heavy metal accumulation

Considering its richness in organic and inorganic mineral nutrients, the recycling of sewage sludge (SS) is highly considered as a soil supplement in agriculture. However, the fate of hazardous heavy metal accumulation in the crops cultivated in SS amended soils is always a source of concern. Since nanoparticles are widely recognized to reduce heavy metal uptake by crop plants; thus, the present experiment deals with okra (Abelmoschus esculentus L. Moench) cultivation under the combined application of SS and TiO₂-nanoparticles (NPs). Triplicated pot experiments were conducted using different doses of SS and TiO₂-NPs such as 0 g/kg SS (control), 50 g/kg SS, 50 g/kg SS + TiO₂, 100 g/kg SS, and 100 g/kg SS + TiO₂, respectively. The findings of this study indicated that among the doses of treatment combinations investigated, 100 g/kg SS + TiO₂ showed a significant (p < 0.05) increase in the okra plant yield (287.87 ± 4.06 g/plant) and other biochemical parameters such as fruit length (13.97 ± 0.54 cm), plant height (75.05 ± 3.18 cm), superoxide dismutase (SOD: 110.68 ± 3.11 μ/mg), catalase (CAT: 81.32 ± 3.52 μ/mg), and chlorophyll content (3.12 ± 0.05 mg/g fwt.). Also, the maximum contents of six heavy metals in the soil and cultivated okra plant tissues (fruit, stem, and root regions) followed the order of Fe > Mn > Cu > Zn > Cr > Cd using the same treatment. Bioaccumulation and health risk assessment indicated that foliar application of TiO₂-NPs significantly reduced the fate of heavy metal accumulation under higher doses of SS application. Therefore, the findings of this study suggested that the combined use of SS and TiO₂-NPs may be useful in ameliorating the negative consequences of heavy metal accumulation in cultivated okra crops.

Nano-fertilizers: A sustainable technology for improving crop nutrition and food security

Excessive use of synthetic fertilizers cause economic burdens, increasing soil, water and atmospheric pollution. Nano-fertilizers have shown great potential for their sustainable uses in soil fertility, crop production and with minimum or no environmental tradeoffs. Nano-fertilizers are of submicroscopic sizes, have a large surface area to volume ratio, can have nutrient encapsulation, and greater mobility hence they may increase plant nutrient access and crop yield. Due to these properties, nano-fertilizers are regarded as deliverable 'smart system of nutrients'. However, the problems in the agroecosystem are broader than existing developments. For example, nutrient delivery in different physicochemical properties of soils, moisture, and other agro-ecological conditions is still a challenge. In this context, the present review provides an overview of various uses of nanotechnology in agriculture, preference of nano-fertilizers over the conventional fertilizers, nano particles formation, mobility, and role in heterogeneous soils, with special emphasis on the development and use of chitosan-based nano-fertilizers.

Diverse biotechnological applications of multifunctional titanium dioxide nanoparticles: An up-to-date review

Titanium dioxide (TiO₂) nanoparticles (NPs) are one of the topmost widely used metallic oxide nanoparticles. Whether present in naked form or doped with metals or polymers, TiO₂ NPs perform immensely important functions. However, the alteration in size and shape by doping results in improving the physical, chemical, and biological behaviour of TiO₂ NPs. Hence, the differential effects of various TiO₂ nanostructures including nanoflakes, nanoflowers, and nanotubes in various domains of biotechnology have been elucidated by researchers. Recently, the exponential growth of research activities regarding TiO₂ NPs has been observed owing to their chemical stability, low toxicity, and multifaceted properties. Because of their enormous abundance, plants, humans, and environment are inevitably exposed to TiO₂ NPs. These NPs play a significant role in improving agricultural attributes, removing environmental pollution, and upgrading the domain of nanomedicine. Therefore, the currently ongoing studies about the employment of TiO₂ NPs in enhancement of different aspects of agriculture, environment, and medicine have been extensively discussed in this review.

Soil Microbial Communities Altered by Titanium Ions in Different Agroecosystems of Pitaya and Grape

Titanium (Ti) is an element beneficial to plant growth. Application of titanium to roots or leaves at low concentrations can improve crop yield and performance. However, the effect of titanium ions on the bulk soil microbial community of planted crops remains unclear. This study aimed to explore the effects of titanium on soil bacterial and fungal communities. Field surveys were conducted to determine the effect of titanium ions on bulk soil microbial communities in pitaya and grape plantations of Panzhihua and Xichang areas, respectively. Full-length 16S rRNA and internal transcribed spacer (ITS) amplicon sequencing were performed using PacBio Sequel to further explore the composition and structure of soil microbiota. The application of titanium ions significantly altered the composition and structure of soil microbiota. Root irrigation with titanium ions in pitaya gardens reduced the diversity of soil fungi and bacteria. However, the decline in bacterial diversity was not statistically significant. Meanwhile, foliar spray of titanium ions on grapes greatly reduced the soil microbial diversity. The bulk soil microbiota had a core of conserved taxa, and titanium ions significantly altered their relative abundances. Furthermore, the application of titanium increased the interaction network of soil fungi and bacteria compared with the control group. Thus, titanium ions potentially improve the stability of the soil microbial community. IMPORTANCE Pitaya and grape are important cash crops in the Panzhihua and Xichang areas, respectively, where they are well adapted. Titanium is a plant growth-promoting element, but the interaction between titanium and soil microorganisms is poorly understood. Titanium ions are still not widely used for growing pitaya and grape in the two regions. Thus, we investigated the effects of titanium ions on soil microbial communities of the two fruit crops in these two regions. Microbial diversity decreased, and the community structure changed; however, the addition of titanium ions enhanced cooccurrence relationships and improved the stability of the community. This study provides a basis for the importance of titanium ion application in crop cultivation.

Effects of Foliar Application of ZnO Nanoparticles on Lentil Production, Stress Level and Nutritional Seed Quality under Field Conditions

Nanotechnology offers new opportunities for the development of novel materials and strategies that improve technology and industry. This applies especially to agriculture, and our previous field studies have indicated that zinc oxide nanoparticles provide promising nano-fertilizer dispersion in sustainable agriculture. However, little is known about the precise ZnO-NP effects on legumes. Herein, 1 mg·L−1 ZnO-NP spray was dispersed on lentil plants to establish the direct NP effects on lentil production, seed nutritional quality, and stress response under field conditions. Although ZnO-NP exposure positively affected yield, thousand-seed weight and the number of pods per plant, there was no statistically significant difference in nutrient and anti-nutrient content in treated and untreated plant seeds. In contrast, the lentil water stress level was affected, and the stress response resulted in statistically significant changes in stomatal conductance, crop water stress index, and plant temperature. Foliar application of low ZnO-NP concentrations therefore proved promising in increasing crop production under field conditions, and this confirms ZnO-NP use as a viable strategy for sustainable agriculture.

Biosynthesis and characterization of titanium dioxide nanoparticles and its effects along with calcium phosphate on physicochemical attributes of wheat under drought stress

Drought stress is reducing the production of crops globally. This research was designed to evaluate the role of titanium dioxide (TiO₂ NPs) nanoparticles and calcium phosphate on wheat facing drought stress. TiO₂ NPs were prepared by green synthesis and their characterization (by UV-visible spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX)) was also done. The results showed that TiO₂ NPs worked efficiently and improved plant growth under drought. However, the best results were obtained from combined applications of 40 ppm TiO₂ NPs and 40 ppm calcium phosphate on plants. They increased root length (33%), shoot length (53%), fresh weight (48%), and dry weight (44%) of wheat as compared to control. The physiological parameters including chlorophyll content, relative water content, membrane stability index, and osmolyte content (proline and sugar) were also improved. The increase in superoxide dismutase, peroxidase and, catalase activity by the combined application of TiO₂ NPs and calcium phosphate was 83% and 78%, 74% and 52%, 81%, and 67% in Pakistan-13 and Zincol-16 respectively, as compared to untreated drought exposed plants. They also enhanced the nutrients uptake (including potassium, phosphorus, and nitrogen) that ultimately improved plant biomass. They also maintained the level of growth hormones in plants. These hormones regulate cellular processes and are responsible for germination, development, and plant reaction in drought stress. The increase in the yield was also significant, hence it is recommended that the 40 ppm concentration of TiO₂ NPs along with calcium phosphate improves the productivity of wheat under drought stress.

Effects of TiO2-NPs pretreatment on UV-B stress tolerance in Arabidopsis thaliana

As the ozone hole in the North and South poles continues to increase, the entire ecosystem will face an environmental crisis caused by enhanced UV-B radiation. Considering the function of TiO₂ and the application of nanomaterials in agriculture, the effect of TiO₂-NPs on UV-B stress tolerance in Arabidopsis was investigated. The phenotype of plants was determined, and the expression patterns of antioxidant systems and related genes were analyzed. Modification of the antioxidant system and changes in the flavonoid content of plants were observed by histochemical staining. The effects of TiO₂-NPs and UV-B on mitosis were observed at the cellular level, and the degree of DNA damage was analyzed by the detection of CPDs content. The effects of TiO₂-NPs and UV-B on SOD isozymes were detected by SOD isozyme Native-PAGE electrophoresis. A laser confocal microscope was used to explore the protective mechanism of TiO₂-NPs against UV-B radiation. Results showed that pretreatment of TiO₂-NPs significantly alleviated the stress of UV-B radiation on plants. TiO₂-NPs activated the antioxidant system of plants, improved the activity of antioxidant enzymes, and promoted the synthesis of flavonoids. Moreover, TiO₂-NPs could effectively shield UV-B radiation to prevent the depolymerization of microtubules in plant cells. 10 mg/L of TiO₂-NPs is a safe and effective application dose, which has no biological toxicity to plants. Our research results reported for the first time that pretreatment of TiO₂-NPs could effectively alleviate UV-B stress to plants, providing new ideas for the application of nanomaterials in agriculture.

Effects of nanoparticles on trace element uptake and toxicity in plants: A review

Agricultural soils are receiving higher inputs of trace elements (TEs) from anthropogenic activities. Application of nanoparticles (NPs) in agriculture as nano-pesticides and nano-fertilizers has gained rapid momentum worldwide. The NPs-based fertilizers can facilitate controlled-release of nutrients which may be absorbed by plants more efficiently than conventional fertilizers. Due to their large surface area with high sorption capacity, NPs can be used to reduce excess TEs uptake by plants. The present review summarizes the effects of NPs on plant growth, photosynthesis, mineral nutrients uptake and TEs concentrations. It also highlights the possible mechanisms underlying NPs-mediated reduction of TEs toxicity at the soil and plant interphase. Nanoparticles are effective in immobilization of TEs in soil through alteration of their speciation and improving soil physical, chemical, and biological properties. At the plant level, NPs reduce TEs translocation from roots to shoots by promoting structural alterations, modifying gene expression, and improving antioxidant defense systems. However, the mechanisms underlying NPs-mediated TEs uptake and toxicity reduction vary with NPs type, mode of application, time of NPs exposure, and plant conditions (e.g., species, cultivars, and growth rate). The review emphasizes that NPs may provide new perspectives to resolve the problem of TEs toxicity in crop plants which may also reduce the food security risks. However, the potential of NPs in metal-contaminated soils is only just starting to be realized, and additional studies are required to explore the mechanisms of NPs-mediated TEs immobilization in soil and uptake by plants. Such future knowledge gap has been highlighted and discussed.

Impact of Superabsorbent Polymers and Variety on Yield, Quality and Physiological Parameters of the Sugar Beet (Beta vulgaris prov. Altissima Doell)

In this study, we focus on the mitigation of the negative impact of drought using the application of superabsorbent polymers (SAPs) to seed. One way to monitor drought and quantify its impact on crops in field conditions is the nondestructive measurement of physiological processes of the crops using spectral indexes LAI and PRI during vegetation. Therefore, during 2018 and 2019, the increase in biomass and intensity of photosynthetic activity was monitored, and the effect of the SAPs application on the yield parameters of the sugar beet was evaluated in the trial conditions (control, SAPs) at the end of the vegetation period. Through statistical analysis, the significant impact (α ≤ 0.01) of SAPs application on the values of spectral indexes LAI and PRI as well as root and white sugar yields was found. Although the sugar content difference between SAPs and control conditions was not statistically significant, SAPs had a positive influence on the value of this parameter. It was found through periodic monitoring of spectral indexes during the growing period that the crop in the SAPs condition showed higher values of PRI at the beginning of vegetation, which was caused by the accumulation of moisture in the vicinity of the seed and subsequent faster growth of roots and photosynthetic apparatus. Moreover, the values of LAI were significantly higher (α ≤ 0.01) in the SAPs condition throughout the vegetation period. In the interaction evaluation, we confirmed that in both years the values of LAI were higher in the condition with SAPs compared with the control. In contrast, the PRI values were significantly different across conditions. The interaction of conditions with variety showed that the variety Brian obtained higher values of LAI and PRI in the SAPs condition. The correlation analysis found a positive correlation between spectral indexes LAI:PRI (r = 0.6184**), and between LAI:RY (r = 0.6715**), LAI:WSY (r = 0.5760**), and PRI:RY (r = 0.5038*), which confirms the close relationship between physiological processes in the plant and the size of its yield.

Green Synthesis of Zinc Oxide Nanoparticles: Fortification for Rice Grain Yield and Nutrients Uptake Enhancement

Applications of metal oxide nanoparticles in the agriculture sector are being extensively included as the materials are considered superior. In the present work, zinc oxide nanoparticle (ZnO NPs), with a developing fertilizer, is applied in the fortification of rice grain yield and nutrient uptake enhancement. To evaluate the role of ZnO NP, two field experiments were conducted during the 2018 and 2019 seasons. ZnO NPs were small, nearly spherical, and their sizes equal to 31.4 nm, as proved via the dynamic light scattering technique. ZnO NPs were applied as a fertilizer in different concentrations, varying between 20 and 60 mg/L as a foliar spray. The mixture of ZnSO₄ and ZnO NP₄₀ ameliorated yield component and nutrients (N, K, and Zn) uptake was enhanced compared to traditional ZnSO₄ treatment. Nevertheless, the uptake of the phosphorous element (P) was adversely affected by the treatment of ZnO NPs. Thus, treatment via utilizing ZnO NPs as a foliar with a very small amount (40 ppm) with of basal ZnSO₄ led to a good improvement in agronomic and physiological features; eventually, higher yield and nutrient-enriched rice grain were obtained.