Advances in Nanotechnology for Sustainable Agriculture: A Review of Climate Change Mitigation

1. Introduction

Nowadays agriculture is facing new challenges that are brought by climate change, the world population steadily needs safe food and high yields to feed all the people (Conti et al., 2021). Although the agricultural sector is one of the first sectors to be affected by climate change, it is also one of the biggest contributors to this phenomenon. It is therefore necessary to modify the entire production process of the agricultural sector so that it can adapt to the inevitable climate change. According to the European Union through the Farm to Fork Strategy, chemical fertilization must be reduced by 20% (Heyl et al., 2023), consequently, new innovative technologies must be applied in agriculture. Climate change affects some parameters (e.g. temperature, area of cultivation, rain patterns) that influence the growth of the main crop for human sustainability (Figure 1).

Table 1. Main nanoparticles used as nano-fertilizers and their effects on plants.

Botanical family	Plant involved	Nanoparticle	Function	Reference
Asteraceae	Helianthus annuus	Si NPs	Head diameter and grain yield enhanced, greater content of oleic acid and linoleic acid compared to the control	Ernst et al., 2023
		ZnO NPs
	Lactuca sativa	ZnO NPs	Biomass, chlorophyll, phenolics, flavonoids, and vitamin C increase	Garza-Alonso et al., 2023
Brassicaceae	Brassica napus	CeO2 NPs	Higher biomass and reduced stress conditions in an salinity-affected environment	Rossi et al., 2016
Cucurbitaceae	Cucumis sativus	CeO2 NPs	Root biomass, Vitamin C and soluble sugar content enhanced, biotransformation of the rhizosphere	Xie et al., 2022
Fabaceae	Glycine max	FeNPs	Number of root nodules boosted and nitrogen-fixing activity increased	Kots et al., 2024
		GeNPs
		CoNPs
	Medicago sativa	TiO2	Stomata opening, antioxidant system, plant height, fresh weight increased	Chen et al., 2024
Poaceae	Oryza sativa	ZnO NPs	Shoot lenght, root lenght and amylase activity improved under cadmium stress	Li et al., 2021
	Triticum aestivum	CuO NPs	Plant height, spike lenght, grain and straw yield increased, pigments content enhanced, stress due to cadmium reduced	Alhaithloul et al., 2023
		CeO2 NPs	Plant conditions improved under cadmium toxicity	Ayub et al., 2023
		Fe NPs	Plant growth enhanced, pigments content and micronutrients uptake increased under salinity stress	Zia-ur-Rehman et al., 2023
Rosaceae	Fragaria ananassa	CeO2 NPs	Yield increase, greater pollen grain numbers and pollen tube elongation, total phenols, Vitamin C and soluble sugar content enhance	Dai et al., 2022
Solanaceae	Solanum lycopersicum	AgNPs	Resistance to abiotic stress enhanced and stress parameters reduced	Narware et al., 2024
		ZnO NPs	Foliar spray increases crop growth and zinc uptake	Sun et al., 2023

Table 1. Main nanoparticles used as nano-fertilizers and their effects on plants.

Botanical family	Plant involved	Nanoparticle	Function	Reference
Asteraceae	Helianthus annuus	Si NPs	Head diameter and grain yield enhanced, greater content of oleic acid and linoleic acid compared to the control	Ernst et al., 2023
		ZnO NPs
	Lactuca sativa	ZnO NPs	Biomass, chlorophyll, phenolics, flavonoids, and vitamin C increase	Garza-Alonso et al., 2023
Brassicaceae	Brassica napus	CeO2 NPs	Higher biomass and reduced stress conditions in an salinity-affected environment	Rossi et al., 2016
Cucurbitaceae	Cucumis sativus	CeO2 NPs	Root biomass, Vitamin C and soluble sugar content enhanced, biotransformation of the rhizosphere	Xie et al., 2022
Fabaceae	Glycine max	FeNPs	Number of root nodules boosted and nitrogen-fixing activity increased	Kots et al., 2024
		GeNPs
		CoNPs
	Medicago sativa	TiO2	Stomata opening, antioxidant system, plant height, fresh weight increased	Chen et al., 2024
Poaceae	Oryza sativa	ZnO NPs	Shoot lenght, root lenght and amylase activity improved under cadmium stress	Li et al., 2021
	Triticum aestivum	CuO NPs	Plant height, spike lenght, grain and straw yield increased, pigments content enhanced, stress due to cadmium reduced	Alhaithloul et al., 2023
		CeO2 NPs	Plant conditions improved under cadmium toxicity	Ayub et al., 2023
		Fe NPs	Plant growth enhanced, pigments content and micronutrients uptake increased under salinity stress	Zia-ur-Rehman et al., 2023
Rosaceae	Fragaria ananassa	CeO2 NPs	Yield increase, greater pollen grain numbers and pollen tube elongation, total phenols, Vitamin C and soluble sugar content enhance	Dai et al., 2022
Solanaceae	Solanum lycopersicum	AgNPs	Resistance to abiotic stress enhanced and stress parameters reduced	Narware et al., 2024
		ZnO NPs	Foliar spray increases crop growth and zinc uptake	Sun et al., 2023

Global warming can put the crop under severe stressed conditions and consequently, this leads to a significant decrease in crop yield. “Paris Agreement” stipulated in 2015 proposed not to exceed the global average temperature by 2 °C. The risks related to breaching this threshold are demonstrated by (Tijjani et al., 2024) who studied the reduction in yields of some crops, specifically up to -14% for maize (Zea mays) and -20% for soybean (Glycine max). In contrast to winter crops such as wheat (Triticum aestivum), Moriondo et al. (Moriondo et al., 2011) show that sunflower (Helianthus annuus) is more affected by heat stress. A key factor that determines the geographic areas in which crops can be grown and influences their growth rate, development and yield is temperature (Ur Rehman et al., 2015). Each crop is characterized by optimum temperature ranges for each phase of the growth cycle. Therefore, temperature fluctuations during the anthesis phase can cause a reduction in yield and disturb crop development (Luo, 2011). According to the Intergovernmental Panel on Climate Change (IPCC Working Group 1 et al., 2013), temperature change in tropical areas has generally harmed food production. However, the increase in maximum temperatures caused by climate change is beneficial for agricultural production in northern locations due to a longer growing season (Cui, 2020; Zhang et al., 2021). However, the negative effects of high temperatures are associated with and aggravated by other environmental factors, such as the frequency of precipitation, the presence of strong winds and the duration and intensity of sunlight. The consequent increase in temperature is correlated with an increase in water demand from the atmosphere, which leads to a consequent reduction in the availability of water to crops and thus a loss of crop yields (Zhao et al., 2017). On the other hand, the increase in temperature leads to indirect effects such as an increase in the frequency of heat waves, the influence on the presence of pests and the development of weeds and crop diseases (Field et al., 2014). Climate change can lead to the adaptation of invasive species, pathogens and pests, to agroecosystems different from their original one (Aluja et al., 2014). Another factor that has a severe impact on crop development is water availability. Climate change affects soil moisture storage, precipitation patterns, evaporation and runoff (Hakimovich and Alishovich, 2023).

Changes in rainfall patterns are of high relevance because more than 80% of the world’s crop production is supplied by rainfall. An increase in the frequency of drought events increases the probability of desertification occurrence (O’Rourke and Petersen, 2016). The main consequences of global warming that may affect plant tolerance and defense include heat stress and drought stress (Faiz et al., 2024). Corn (Z. mays), pea-barley (Lathyrus oleraceus) and wheat (T. aestivum) yield loss are limited under this condition (Wittwer et al., 2023). Considering that new strategies and sustainable practices must be adopted. For example, chitosan, which is obtained from arthropods or insects, and microbe-based biofertilizers can improve thermal tolerance by increasing plant’s immunity, antioxidants and hormones production, boosting nitrogen fixation, phosphorus dissolution in soil, crop biomass and photosynthesis rate; all of these considerations lead to better crop productivity and a greater yield (Dastogeer et al., 2022; Toaima et al., 2023). An innovative technology that can help in achieving this goal is represented by nanoparticles. The use of nanoparticles (NPs) could be a solution to alleviating situations and stresses caused by climate change. In fact, NPs are widely used in the agri-food chain, they can improve nutrients uptake in plant, they can enhance plant defense against biotic and abiotic stress and they can favor shelf-life products avoiding toxins presence (Mukarram et al., 2022). Indeed, its use has a promising impact on morphological, biochemical and physiological crop traits (Mahmoud et al., 2023), they allow an herbicide precise dose application (Amna et al., 2019) and they guarantee a better food coobservability (Bamisaye et al., 2023). This review aims to analyze the benefits and negative effects of the use of nanoparticles for reducing the influence of climate changes on agricultural chemical inputs, the control of crop pests and pathogens and food health and security. Furthermore, the following review reports the three areas where NPs are mainly employed: fertilization, weed management and food quality.

1.1. Climate Change on Fertilization

Conventional agriculture, over decades, has brought an increase of input inside the agroecosystem, such as heavy machines, fossil fuels and fertilizers compromising the natural fertility of the soil. During the last century, synthetic fertilizers have dramatically increased crop production per cultivated area. Both the production and application of fertilizers have a heavy impact on emissions. Fertilizers are widely used in supporting agricultural production and their high nitrogen and phosphorous content can lead to increased emissions of greenhouse gases (GHGs), including nitrous oxide (N₂O) and ammonia (NH₃), which can contribute to global warming. The use of the main fertilizers most important, containing nitrogen (N), phosphorus (P) and potassium (K) has increased considerably over the last 40 years, especially for nitrogenous fertilizers. Furthermore, while the use of phosphate and potash fertilizers has stabilized, especially in the last 20 years, the use of N fertilizers continues to increase (FAOSTAT, n.d.). If conventional agriculture is combined with climate change the situation is even more critical. Indeed, temperatures are increasing, and precipitations have become irregular and abundant. These phenomena, changing soil moisture and soil aeration, can result in nitrogen leaching (NO₃^-) and volatilization (NH₃) contributing to eutrophication (Li et al., 2024). In parallel to nitrogen, climate change creates problems in phosphorous management, affecting overall crop production. P availability, uptake and translocation are affected by fluctuations in temperature, pH, drought and CO₂ (Short et al., 2016). In fact, extremely low or high soil temperatures reduce P uptake and translocation. Furthermore, alkaline soil pH affects P concentration and decreases its uptake rate by plants. While, an acidic soil pH reduces the activity of soil microorganisms, the transpiration rate and the uptake and utilization fertilizer of P. Finally, increased CO₂ concentration reduces the uptake of this macro element from the soil by plants (Maharajan et al., 2021). Regarding the connection between excessive fertilizer use and increased CO₂ emissions, Guo et al. (Guo et al., 2022) showed that China’s excessive carbon dioxide emissions are due to the excessive use of chemical fertilizers in agriculture. Since mineral fertilizer application can bring these problems just listed, new technologies are required. Indeed, instead of using common fertilizer, it is possible to apply nano-fertilizer which is more sustainable, requires less quantities and boosts nutrient use efficiency in crops.

1.2. Climate Change on Agrochemicals

It is important to know that 99% of all synthetic chemicals, including pesticides, are derived from fossil fuels (CIEL, 2022). In addition to the production phase, pesticides can also release greenhouse gas emissions after their application. It has been shown that the application of fumigant pesticides can contribute to a significant increase in nitrous oxide production in the soil (EPA, 2012; Spokas and Wang, 2003). However, even if pesticide use is at one of the origins of climate change, studies show that the effects of climate change are likely to lead to an increase in the use of synthetic pesticides (Choudhury and Saha, 2020). This is mainly due to a reduction in the ability of crops to resist abiotic stresses, such as drought conditions that weaken the crops' natural defenses and change their biology, making them more vulnerable to pests (Guo et al., 2017; Taylor et al., 2018). In addition, rising temperatures are likely to stimulate the growth of pest insect populations in some regions, and there will be a change in the geographic regions of some insects and their potential winter survival rate (Jones et al., 2017; Lesk et al., 2017; Skendžić et al., 2021a). Tonnang et al. (2022) predicted that the increase in CO₂ and temperature will lead to an acceleration in the metabolism and consumption of insect pests, leading to a decrease in crop yields. Furthermore, Thomson et al. (2010) predicted that the effects of climate change could cause pests to migrate to new areas where their natural enemies are absent, or cause a shift in life cycles, reducing the possibility of natural control. Some studies found that certain climatic changes affect different pests in different ways. For example, Pathak et al. (2012) demonstrate that smaller pests, such as aphids, mites or whiteflies, can be washed away during intense precipitation. Moreover, with the increase of periods of prolonged precipitation, plant fungal and bacterial diseases can become more common (Sutherst et al., 2011).

Therefore, climate impacts will have a significant influence on which pests become more prevalent for each specific region, crop, and pest. In addition, rising CO₂ and temperature are likely to increase the pressure of weeds on cultivated crops. Weeds, having a diverse gene pool and greater adaptive capacity are more likely to be resilient and better adapted to the effects of climate change than cultivated crops (Varanasi et al., 2016). Increased carbon dioxide levels can probably increase the size and height of weed seeds, increasing their wind dispersal (Ziska et al., 2011). Moreover, Rodenburg et al. (Rodenburg et al., 2011, 2010) demonstrated that changes in rainfall patterns alter weed seed production and dispersal. Anwar et al. (2021) suggest that weeds will have a greater ability to compete with crops in many regions, leading to decreased yields. Similarly to pathogens, climate change is also capable of introducing weeds into new regions and changing regional species composition, particularly favoring invasive species (Peters et al., 2014). Regarding the durability of pesticides, the expected increase in temperatures will cause greater volatilization of the compounds, reducing their efficacy (Noyes et al., 2009). Bailey (2004) reported that increasing soil temperatures cause shorter duration of herbicides for weed control due to faster degradation. Conversely, low soil moisture has been linked to slower degradation of herbicides. Therefore, climate change will accelerate the degradation of pesticides, reduce their use for a shorter time and farmers will have to increase pesticide application rates (Choudhury and Saha, 2020; Delcour et al., 2015). The introduction of the use of nano-herbicides, with lower and more accurate application, can reduce the use of traditional agrochemicals and improve the effectiveness and efficiency of pest defense.

1.3. Climate Change on Post-Harvest

Climatic factors, such as temperature, precipitation and atmospheric CO₂ concentration, influence fungal colonization and mycotoxin production (Magan et al., 2003). Therefore, fluctuations in these factors may lead to an increase/decrease in the relative risk of mycotoxin contamination during both field and post-harvest cultivation. Global warming not only has an impact on host-pathogen interactions but may favor the emergence of new diseases and changes in fungal biodiversity/microbiome and influence the geographic distribution of crops, pathogenic fungi and thus the mycotoxins they produce (Paterson and Lima, 2011, 2010). In addition, due to changes and alterations in the phenology of host plants (Jeger et al., 2007) and changes in the distribution and temporal activities of fungal pathogens (Desprez-Loustau et al., 2007; Shaw et al., 2008) will have both economic and social implications and costs (Bebber et al., 2013; Medina et al., 2015). Climate change not only brings problems during crop cultivation but there are also impacts on the shelf life of harvested products.

High temperatures can accelerate ripening resulting in fruits being less turgid and consequently less durable over time, other most common problems in post-harvest are fruit water loss, tissue fragility and surface browning due to mechanical injuries (Badiee et al., 2023). Moreover, global warming is causing fungal spores spreading which threaten fruit conservation and product quality by becoming dangerous for human health. Indeed, a study conducted by Thole et al. (2021) demonstrated that temperature increases can reduce fruit shelf-life by three to five days while fungal susceptibility is enhanced by 6% to 16%. Moreover, microorganisms can be a risk also for dried fruits, indeed fungi such as Aspergillus spp. can survive the drying process remaining dormant for a long period. Dried fruits more affected are apricots, vine fruits, figs, mulberries and prunes. Mycotoxins which are mostly produced by fungi and found in products are aflatoxins (AFs) and ochratoxin A (OTA). These mycotoxins are a global issue because they are heat-stable hence they survive heating processes (González-Curbelo and Kabak, 2023). Hence it is fundamental to prevent their creation by keeping low seed moisture content (SMC), guaranteeing both food safety and seed nutritional quality. In fact, an experiment conducted by Granado-Rodríguez et al. (2022) showed that when placing quinoa (Chenopodium quinoa) seed at an SMC between 5% and 12% the nutritional status is safeguarded. Spores spreading and high moisture levels can be avoided by using new innovative technologies able to reduce water content in the air, this solution can be found by taking advantage of nanoparticles.

2. Nanoparticles in Agriculture

Nanotechnologies can represent an alternative to synthetic compounds widely used in agriculture, reducing the environmental impact of traditional applications. Nanoparticles (NPs) can be applied at very low concentrations, minimizing the doses and frequency of treatments. NPs are characterized by having small dimensions (range of 1 to 100 nm), with unique surfaces and properties, allowing them to enter and interact with plant cells and tissues compared to the same material in another form (Qazi and Dar, 2020) (Figure 2).

Nanoparticles knowledges about their translocation mechanisms are limited, a study conducted on wheat and reported by (Zhu et al., 2020) found out that ZnO NPs can enter to the leaf epidermis through stomata. After that they pass through apoplastic pathway, lately a fraction of ZnO NPs dissolves in the apoplast releasing Zn cations while the remaining fraction is absorbed by mesophyll cells. Hence, this study demonstrates that stomata play a pivotal role in NPs mechanism of action. Nanoparticles can be applied also as a root application, in fact Iannone et al. (2016) stated that Fe₃O₄ nanoparticles are absorbed by roots and translocated thanks to apoplastic pathway in root cells. These NPs are not subjected to aerial part uptake but they contribute to enhance antioxidant enzyme activities improving roots defense.

Other nanoparticles, such as silica ones, follow the sap flow using simplastic and apoplastic pathway and finally they reach stem and leaves (Sun et al., 2014). In addition, trace elements such as selenium, in the form of NPs, are able to be absorbed by the roots and be transported to the aerial part leading to biofortification (Lyu et al., 2022). The development of nanoparticles with specific functions can be a possible solution to problems related to the development of crops, and the reduction of the use of fertilizers and pesticides. Vijayakumar et al. (2022) collected the various applications of nanoparticles in agriculture, focusing mainly on their function in stimulating and improving crop growth. In particular, they investigated how applying NPs in the form of nano-fertilizers (NFs) and nano-pesticides (NPs) makes the uptake of nutrients or chemical compounds of pesticides more effective by increasing the production and protection of plants against diseases. It is important to know that the effectiveness and responses of the plant to the presence of nanoparticles depend on their size and concentration. Furthermore, each crop reacts to the presence of NPs in the environment by expressing changes in morphological, physiological but also biochemical characteristics (Tolisano and Del Buono, 2023). Moreover, recent studies have demonstrated that nanoparticles can also influence seed germination, promoting seedling development by increasing cell division and enhancing certain biochemical pathways (Nguyen et al., 2022; Pereira et al., 2021). According to available published literature, the two main methods of NP application in crops are foliar treatment and root exposure (Khan et al., 2022). In the case of in vitro applications, nanoparticles can be added to culture media (Sarkar and Kalita, 2023). In addition to being a solution in nutritional and pathogenic control aspects in field crops, nanoparticles are a useful technology in the conversion of waste material to energy, in food preservation (Zhang et al., 2016).

Even though nanoparticles have many beneficial applications, it is necessary to assess all the risks that their use in the agricultural sector may cause in terms of the environment and the food chain (Qazi and Dar, 2020; Rico et al., 2011). According to Bhattacharjee et al. (2022), negative impacts on crops are generally found when the application of NPs is elevated and unresponsible. However, the available literature on this topic shows that using reasonable concentrations of nanoparticles which are appropriate to the treated crop helps to avoid harmful effects and achieve the desired benefits (El-Moneim et al., 2021; Ghani et al., 2022; Sun et al., 2020; Wang et al., 2022).

2.1. Nanoparticles as Nano-Fertilizers and Biofortificators

The two main problems with traditional phosphorus- and nitrogen-based fertilizers are their low nutrient uptake efficiency and rapid transformation into chemical forms that cannot be used by plants, leading to negative impacts on the soil and the environment, with an increase in hazardous greenhouse gas emissions and eutrophication (Raliya et al., 2018). Therefore, the use of innovative technologies such as nano-fertilizers, which gradually release nutrients, help to significantly reduce nutrient loss while ensuring environmental safety and play a significant role in maintaining soil fertility and improving crop yields (Congreves and Van Eerd, 2015; Ghormade et al., 2011).

Nanoparticles can be used as fertilizer by foliar application leading to a yield and growth improvement, furthermore, their distribution can improve plants' performance in facing pests and diseases. Indeed, nano-fertilizers: (1) provide plants with appropriate nutrients via foliar and soil applications, (2) increase the chlorophyll content in leaves (enhancing photosynthesis) (Thavaseelan and Priyadarshana, 2021), (3) are cost-effective resources, (4) have high efficiency (Zahra et al., 2022), and (5) play a key role in pollution prevention (Guru et al., 2015), (6)enhance the tolerance of plants to cope environmental stresses (salinity,drought) (Al-Mamun et al., 2021).The main ones contain zinc (Zn), calcium (Ca), manganese (Mn), silica (Si) and iron (Fe) oxide (Al-Antary and Ghidan, 2023; Yadav et al., 2023) (Figure 3).

Furthermore, with regard to the supply of macronutrients such as nitrogen, phosphorus and potassium, which is more problematic from an environmental point of view, the use of NFs based on these elements reduces the risks associated with traditional mineral fertilization and allows other important plant growth objectives to be pursued (Basavegowda and Baek, 2021; Sheoran et al., 2021)(Table 2).

Indeed, nitrogen nano-fertilizers not only improve the efficiency of use, but also reduce the leaching of this element thus reducing eutrophication and greenhouse gas emissions (Mejias et al., 2021). A study conducted by Sharaf-Eldin et al. (2022) stated that nano-nitrogen applied in combination through drip irrigation (75%) and foliar application (25%) can lead to a better yield if compared to common nitrogen fertilizers. On the other hand, also zinc is very important in the soil-plant-human system, inside plants it has a pivotal role in metabolism, it is part of many enzymes, it is involved in protein and RNA synthesis, and it contributes to membrane stability by scavenging reactive oxygen species (ROS). Zn deficiency can lead to delayed maturity, reduced grain yield and even high mortality, this is most likely to happen in crop species such as rice, wheat and tomato which are low tolerant to Zn deficiency (Natasha et al., 2022). Manganese is another pivotal microelement for plant development, it is involved in ROS detoxification, it has a main role in the first part of photosynthesis (water-splitting reaction in PSII), it contributes to lignin biosynthesis. Mn deficiency can lead to a decrease in biomass, in chlorophyll content and in the number of chloroplasts; it also causes high susceptibility to plant diseases (Alejandro et al., 2020).

Silica is mainly found as silicic acid Si(OH)₄, this element can help plants in improving cell wall resistance thanks to silica bodies called phytoliths, it creates a physical barrier against pathogens and it enhances enzyme activity and endurance against biotic and abiotic stress (Currie and Perry, 2007). Si deficiency may reduce photosynthetic activity and grain yield (Chaiwong et al., 2021). Nano-fertilizer can be a promising approach in agriculture because of their effect on plants: their application can reduce nutrient requirements by plants and nutrient loss by leaching, moreover, they can increase low crop productivity and alleviate abiotic stress (Saraiva et al., 2023). Climate change can induce different kinds of stress inside the plant, for example, drought stress can cause growth slowdown, photosynthesis mitigation and stomatal closure (Lv et al., 2023). This stress can be reduced by using microelements or amino acids such as zinc and proline which can be sprayed on plants. For example, Hanif et al. (2023) demonstrated that proline-coated ZnO (ZnOP) NPs can increase shoot length, dry weight, and reduce flavonoids and phenolics concentrations.

Zinc-oxide nanoparticles (ZnO-NP) have a good response also in up taking nutrients application on seeds can enhance phosphorus uptake, chlorophyll and pigment content; while if applied through foliar spray to maize (Z. mays) plants it can enhance growth even of 11% (Ahmad et al., 2023). Hence nano-fertilizers bring also biofortification to crop physiology, a study conducted by Palacio-Márquez et al. (2021) showed that Zn can be applied also as zinc nitrate complexed with chitosan which can favor biomass accumulation and production, photosynthetic activity, total chlorophyll, amino acids and carotenoids increase; conversely, ZnO can accelerate plants maturation anticipating the harvest in green bean (Phaseolus vulgaris).

Also, magnesium (Mg) can be used as a nanomaterial able to mitigate drought stress, it can be applied as MgO and MgCO₃. According to Silva et al. (2023), this nanoparticle treatment can lead to chlorophyll a, b and carotenoid accumulation in lettuce (Lactuca sativa). Another important compound which can prevent abiotic stress is salicylic acid (SA), in fact, due to climate change and abundant precipitation plants can live in anoxia periods. An experiment reported by Errázuriz-Montanares et al. (2023) found that root submersion stress in cherries (Fragaria ananassa) can be alleviated by applying on the leaf SA, this application at preharvest and postharvest can result in improving stomatal conductance and transpiration implying a better leaf gas exchange response and consequently an improved physiological situation. Also, selenium (Se) can be used as a nano-priming agent Setty et al. (2023) reported that soaking rice (Oryza sativa) seeds with different concentrations of Se nanoparticles (SeNPs) can lead to faster germination and imbibition. SeNPs can allow a quick water flow inside the cell, moreover, these nanomaterials enhance alpha-amylase activity bringing higher starch consumption and faster seedling growth.

Cerium oxide (CeO₂) is a rare earth element, it shows interesting results in the most cultivated crops, and it has been demonstrated that its application at low concentrations has a positive effect on many crop species. The following studies come into disagreement since in the first case cerium caused phytotoxicity while in the second one, it reported many improvements. A study conducted in the Mediterranean region showed unexpected results: in a seed trial CeO₂ reduces total root length while in barley (Hordeum vulgare) life cycle study negatively affects potassium and sulfur uptake (Mattiello et al., 2016). On the other hand, another experiment performed by Rico et al. (2014) on wheat (T. aestivum) reported that CeO₂ can improve plant growth, shoot biomass, and grain yield. These studies indicate that sometimes the effectiveness of an application may depend on the species and nanomaterial nature.

Research that concerns wheat resistance to salt stress tested many nanoparticles based on zinc, aluminums, copper, and iron. The study showed that each element gives an effect for a specific parameter: Fe₃O₄ accelerated germination parameters, shoot length was increased by ZnONPs, CuO increased chlorophyll a, b and carotenoids content (Olatunbosun et al., 2023). However, the application of incorrect quantities of nano-fertilizers may cause negative effects due to nutrient toxicity (Hammok and Saeed, 2024). Before using this technology on a large scale, it is important to know the effects of nano-fertilizer degradation on crop growth and soil fertility. For these reasons, it is important to know how the structure (size, solubility, type of materials) and composition of NFs interact with climatic conditions (drought phenomena, heat waves, flooding) and soil parameters (ionic strength, organic matter content, pH, electrical conductivity and phosphate concentration) (Ameen et al., 2021; Dimkpa, 2018). Read et al. (2016) showed that when the soil pH is acid ZnO NPs change into iones very rapidly, whereas when the pH is alcaline the NP tend to be bounded. Shah et al. (2014) demonstrated that, ZnO and CuO did not play a significant role in the shifting of the microbial community structure. Instead, silver nanoparticles were the cause of the changes in the microbial community. Although, Asadishad et al. (2018) found that nanoparticles of CuO, ZnO, and Ag are toxic to soil microbes at concentrations between 1 and 100 mg/kg, but nanoparticles of titanium oxide (TiO) are not toxic at these levels. One of the most important aspects to consider is the dose of nano-fertilizer in each application. Indeed, improper doses, whether higher or lower, can cause toxic effects on crop health and production (Amirnia et al., 2014) and soil (Suresh et al., 2013). For example, Chai et al. (2015) demonstrated that the application of nano-fertilizers based on ZnO, TiO₂ and CeO₂ can cause the inhibition and reduction of enzyme activity and abundance of functional bacteria. Furthermore, Morales-Díaz et al. (2017) argue that the use of nano-fertilizers based on ZnO, TiO₂, Fe₃O₄ causes a reduction in microbial biomass in the soil, reducing soil enzyme activities. Similarly, Jośko et al. (2014) showed that high application doses can negatively affect the activity of the dehydrogenase enzyme. Therefore, these studies, by highlighting the critical issues in the application of nano-fertilizers, demonstrate the need to clarify the interaction between the application of NFs and the factors involved in the improvement of crop growth and productivity. Finally, it is important to carry out further studies to identify the optimal dose to eliminate the harmful effects that NFs can cause on crops and soil.

2.2. Nanoparticles as a New Strategy in Weed and Pests’ Management

In modern agriculture, the use of agrochemicals is typically aimed at protecting cultivated plants from pests (pathogens, harmful insects, parasitic weeds) that impair their production and productivity. European Green Deal asks to reduce by 50% pesticide application including herbicides (Triantafyllidis et al., 2023), hence innovative and sustainable products must be studied. It is well-known that herbicide overuse can lead to greenhouse gas emissions, and biodiversity loss and favor herbicide-resistant species (Narayana Rao and Korres, 2024).

A new strategy in weed management, during this climate change era, can be represented by nano-herbicides (NHs), these new nanotechnologies are seen as a promising finding between agrochemicals. Nano-herbicides can guarantee low toxicological implications and just a few residues in soil and environment, since they have a specific target low quantities are required and costs are reduced (Amna et al., 2019)(Table 2). Mainly, NHs are applied as a foliar spray, they enter inside the stomata and then they use the xylem or the apoplast transportation to reach the membrane (Akintelu et al., 2023). They are built with eco-friendly materials, consequently their toxic accumulation is avoided in crops and soil (Dong et al., 2023). This new kind of application has been tested also on seeds, an herbicide called 2-methyl-4-chlorophenoxyacetic acid (MCPA) has been encapsulated in a zinc-layered hydroxide (ZLH) creating a zinc-layered hydroxide-2-methyl-4-chlorophenoxyacetic acid (ZMCPA). This engineered herbicide reduced the chlorophyll of the plant, destroying vascular growth and causing cells to burst (Johari et al., 2023).

MCPA is persistent in the soil just for a month, anyway, it may still be able to damage nontarget organisms, hence, using ZLH as a nanocarrier can be a sustainable solution to avoid environmental risk. This nano-formulation has been tested also on weeds by lowering pigment content, number of leaves and plant height (Hasrin et al., 2023). Also, element-based nano-formulations can result in having an herbicidal effect, in fact, silver nanoparticles (Ag NPs) can be obtained from a botanical biosynthesis. Ag NPs can alter Bidens pilosa development by arresting seed germination and seedling growth (Jiang et al., 2023). An experiment conducted by Khan et al. (2023b) tested two nano-herbicides wrapped by a chitosan matrix, the study reported that both clodinofop propargyl and fenoxaprop-P-ethyl can be used to reduce Avena fatua and Phalaris minor growth in wheat (T. aestivum) field. The same author filled chitosan nanoparticles with mesosulfuron methyl + florasulam + MCPA isooctyl, this nano-herbicide applied at the recommended dose of normal herbicide showed a mortality of 100%, consequently at this treatment plant height, chlorophyll content, fresh and dry biomass are not reported (Khan et al., 2023a). It is important to study this new nanotechnology to assess its potential phytotoxicity, indeed research conducted by Evy Alice Abigail (2019) used biochar (BC) as nano-sorbent creating a nano-formulation with 2,4-dichlorophenoxyacetic acid (2,4-D), this experiment showed that 2,4-D+BC affected weed growth without reducing maize (Z. mays) biomass. NPs can be useful also for insects’ reduction, due to climate change these pests are spreading and they are causing several damages to crop production. Furthermore, because of temperature increase, new habitats are becoming available for allochthonous species putting at risk crop production (Rocchia et al., 2022). Hence new strategies, such as nanoparticles, must be studied to face these problems brought by climate change. Indeed, some preliminary studies conducted in vitro on mealybug (Puto barberi), which cause damage to plants roots, have already reported that a ZnO-NPs 300 ppm suspension can bring a 55% mortality, in fact this type of NPs has the ability to dehydrate the phytophage cuticle (Agredo-Gomez et al., 2024).

ZnO-NPs have been showed to be promising also by Rebora et al. (2023), in fact zinc nanoparticles have the property of binding to attachment structures (Pulvilli, hairy pads, claws), in this way NPs inhibit the attachment mechanism to surfaces in Hemiptera insects such as Nezara viridula. Another inhibition technique is represented by silicon NPs, in fact, if insects feed on plants treated with SiNPs this can result in nanoparticle accumulation inside the gastrointestinal tract and digestion is avoided (Bhatnagar et al., 2024). Furthermore, iron nanoparticles (FeNPs) obtained from Trigonella foenum-graecum extract can increase Helicoverpa armigera and Spodoptera litura mortality by having an antifeedant effect (Muthusamy et al., 2023). S. litura larvae has shown also a 100% mortality at ZnO-NPs application, these NPs make insects unable to develop a physiological defense (Thakur et al., 2022). A larvicidal effect has been reported also by Shahid et al. (2022) silver nanoparticles, AgNPs are able to penetrate through cuticle and then they bind themselves with phosphorous and sulfur proteins causing cell membrane instability.

Hence these new nanotechnologies are important because they can (i) reduce synthetic pesticide application and consequently they mitigate climate change, then (ii) they represent an eco-friendly and cost-effective solution for the environment and for farmers (Shahid et al., 2022). Due to the long-term release of the active ingredient being one of the main purposes for which nano formulates are developed, it is important to understand their capacity and degradation rate in the environment. The incorrect use of this nanotechnology can affect living organisms negatively, as they are characterized by their very small size and can accumulate in the food chain and be transported by air, causing damage to human and animal health. In addition, nano-herbicides can block the flow in the vascular bundle of plants and reduce pollination. Moreover, have negative impacts on soil microbial communities and some algae (Muchhadiya et al., 2022). Despite the reduction in the amount of active ingredient used in nano formulations Kah et al. (2013) through a study suggested that these applications could also be toxic to non-target organisms. However, nano pesticides, like conventional ones, can also be subject to leaching following rainfall events, causing negative environmental effects (Bombo et al., 2019). Despite this, Gao et al. (2018) reported that nano-formulations cause, unlike conventional pesticides, less environmental pollution due to lower application rates and reduced losses. Therefore, investigation is required on the ability of these nanoparticles to produce toxic effects through their bioaccumulation in the soil and their translocation in different environmental sectors up to the food chain (Huang et al., 2018; Hayles et al., 2017).

2.3. Nanoparticles, Pre- and Post-Harvest Preservation, Food Quality and Packaging

Climate change exposes food factories to many challenges, such as food production and its conservation, due to global warming numerous pathogens such as fungi proliferate and produce toxins that threaten food production. Nanoparticles called nano-emulsions (NEs) can be used in the food industry to deal with food quality and packaging, but also as carriers able to incorporate healthy compounds inside the finished product. Moreover, NEs improve texture, nutrient quality, taste and resistance against unwanted microorganisms (Bamisaye et al., 2023). Nano-emulsions can be used in food packaging with coatings and films extending shelf-life products, furthermore, they can be used singularly as edible envelopes capable of bringing flavorings, colorings, useful enzymes and antioxidants (Gupta et al., 2023).

Crop storage and processing can be altered because of mycotoxins, one of these produced by Aspergillus spp. is called aflatoxin: this compound is carcinogenic and teratogenic, it is dangerous for humans and animals' health, moreover, reduces cereal quality production. It has been reported by Loi et al. (2023) that it is possible to use nanomaterials called magnetic nanoparticles which are able, thanks to their metal nature, to bind mycotoxins and spoil them. Climate change challenges are represented also by fruits and vegetable post-harvest durability over time, hence new conservation strategies must be found, in this way, it would be possible to reduce post-harvest losses. A study reported by Hussain et al. (2020) stated that it is impossible to improve fruits and vegetables' shelf-life through a new process called desiccant air-conditioning (DAC) system, this new kind of storage can solve problems brought about by climate change such as high transpiration and respiration in postharvest. DAC consists of two phases, the first one which is called dehumidification uses nanoparticles as a silica gel that can absorb air moisture. The second phase, regeneration, restores starting conditions. Mariadoss et al. (2019) showed that synthesis, through aqueous extract of Punica granatum peel, of zinc oxide nanoparticles can be effective as antibacterial agents against standard strains of Staphylococcus aureus and Escherichia coli (Ghidan et al., 2017). In other hands, nanoparticle application can bring an alleviation from toxicity present in the soil that could interfere with plant growth and production, both in quantity and quality, creating a threat to consumers.

An example of phytotoxicity in the soil is brought by heavy metal, cadmium (Cd) excessive uptake and accumulation are becoming very common in plant tissues, in the environments and the crop fields. The combined foliar application of chitosan and putrescine as nanoparticles (CTS-Put NPs) can increase chlorophyll and carotenoid content in grapevine (Vitis vinifera), they improve chlorophyll fluorescence parameters and reduce Cd content in leaves and roots (Panahirad et al., 2023). Another toxic element is arsenic (As) which is naturally found in the soil, firstly it reduces root growth damaging cell membranes, lowering nitrogen and sulfur assimilation and decreasing plant transpiration and biomass. In plants such as soybean (G. max) As exposure reduces the number of nitrogen-fixing root nodules, this stress can be neutralized thanks to magnesium oxide nanoparticles (MgO-NPs) which can improve plant height, dry weight, net photosynthesis rate and stomatal conductance in stressed plants (Faizan et al., 2022; Finnegan and Chen, 2012). Another element which can interfere with plant growth is aluminum (Al), its high presence can stop elements uptake (phosphorus, calcium, potassium, magnesium) by restricting roots. Carbon loaded with tungsten oxide has proven to remove Al³⁺ from soil (Shetty et al., 2021). Despite the many advantages of this nanotechnology, however, it is important to understand the importance of the stability of the nano-emulsion formulation used. These are influenced by parameters such as temperature and pH, which can affect the solubilization of the applied substances (Mishra et al. 2014). In addition, characteristics such as input availability, kinetics, acceptability and polarity are also relevant aspects to be taken in consideration when developing NEs. Being that surfactants/surfactants are present in the formulation of NEs, in addition to nanoparticles, it is important to understand their fate in the environment and in the food chain (Bajpai et al. 2018).

In a review, Loira et al. (2020) recommended delaying the use of these new technologies in the food industry because these issues are not fully understood. Smolkova et al. (2015) discussed the effects that bioaccumulation of nanoparticles can cause at the epigenetic level. Gaillet and Rouanet (2015) suggested that Ag NPs can cause inflammation in the intestinal tract. Negative effects have also been observed in NPs based on CuO (Naz et al., 2020) and on ZnO (Czyżowska and Barbasz, 2022). However, the point remains that the toxicity of a metallic nanomaterial may vary depending on the state of oxidation, binders, solubility and morphology, as well as environmental and health conditions (Sengul and Asmatulu, 2020). Moreover, is important to realise that toxicity is given by the dose, exposure time, surface coating characteristic, and especially the size of the nanoparticle (Maynard et al. 2006). Although the use of nanotechnology at the food level does not yet have legislation (Linsinger et al. 2013), EFSA Scientific Committee in 2018 has published a paper assessing the risks and making suggestions in the use of nano-emulsions in the food sector.

3. A bibliometric Analysis of Nano-Particles Used in Agriculture for Cope Climate Change

3.1. Preface

The climate change affect negatively agricultural system, including global warming (Lionello and Scarascia, 2018), change of rainfall pattern (Trenberth, 2011), and weed and pests spread (Skendžić et al., 2021b; Storkey et al., 2021). In the challenge of climate change mitigation, the use of nanotechnology is key to addressing today's increasingly important issues for environmental sustainability. In particular, the use of nanoparticles appears to be of recent interest in solving various problems related to conventional agriculture and climate change. Using nanoparticles as containers, they can be used in the agricultural sector as a means of transporting fertilizers, agrochemicals and post-harvest food durability products. Among other advantages, it is useful to say that through foliar or root applications, nanoparticles deliver nutrients more effectively and efficiently while reducing the amount of fertilizer. This is also important in the application of pathogen and weed control treatments, where there is less input of agrochemicals and better control. A bibliometric analysis was conducted to review the nanoparticles-related studies in the worldwide literature from 2014 to 2024 to provide information on specific aspects over time, to identify current research trends, to highlight the importance and to understand the research progress and future studies regarding these nanotechnologies.

3.2. Methodology

The Scopus database was used in this study to collect the set of published articles on the topic of nanoparticles research. The search query (Figure 4) is selected in the Scopus database as TITLE-ABS-KEY (“nanoparticles” AND “climate change” AND “agriculture”).

The search performance was carried out in March 2024 and resulted in 186 articles. The table of documents is exported in CSV format and the database file is then used as the input data for bibliographic analysis. The search retrieved 186 documents which had studies conducted in 16 different countries from 2014 to 2024. VOS viewer (van Eck and Waltman, 2010) was utilized to construct and visualize the different networks used in this work. In addition, an analysis was conducted to observe how the nanoparticles (NPs) theme is related to other important topics such as: the presence of insects that due to climate change are reproducing very fast causing enormous damage, the proliferation of weed that reduce yields, fertilization that can be improved thanks to NPs, food security that is becoming increasingly important, and plant growth that can be helped thanks to micro- and macro-nutrients in the form of nanoforms. Queries used are respectively TITLE-ABS-KEY ("nanoparticle" AND "insect"), TITLE-ABS-KEY ("nanoparticle" AND "weed"), TITLE-ABS-KEY ("nanoparticle" AND "fertilization"), TITLE-ABS-KEY ("nanoparticle" AND "food security") and TITLE-ABS-KEY ("nanoparticle" AND "plant growth"). Later for each query a bar chart was produced reporting for each related nanoparticle topic the number of documents published over years. All the documents found in the queries (5318 results) were used to create stacked bar charts that report which are the topics related to NPs mainly studied in the last ten years and their percentage frequency of study.

3.3. Results and Discussion

3.3.1. The Geographical Distribution of Publications and Top Contributing Organizations

Figure 5 represents the geographical distribution of publications including the keyword “nanoparticles” in Scopus from 2014 until 2024 showing the top countries in the field of NPs research in terms of the number of publications. India (76 articles) has the highest publication number in the field, followed by China (22 articles) and Egypt (19 articles), United States (18 articles), Pakistan (17 articles) and Italy (11 articles).

Other countries such as Iran, Russian Federation, United Kingdom and Saudi Arabia have almost less than 10 numbers of articles. The study of nanotechnology has the potential to open up new horizons in research and development in various disciplines, ranging from healthcare/medicine, electronics, agriculture, water treatment, food processing and cosmetics. Many of these applications are very relevant to developing countries like India. The development of nanotechnology in this country was conceived and pursued primarily on the premise that this new and emerging technology has the potential to help the population address social challenges such as drinking water supply, healthcare, etc. Therefore, since the early 2000s, the Indian government has played a pioneering role in fostering and promoting nanotechnology research and development in the country (Kumar, 2014). This is the reason why India is the most prolific country in terms of publications on this topic. Instead, the fact that China is one of the most productive countries in nanoparticle research may be because this nation's scientific interest in the development of nanoscience and nanotechnology has been high since its initial stage (Bai, 2006).

3.3.2. Most Influential Publication

Tang et al. (Tang et al., 2017) is the most cited paper with 338 publications, this article explains how cellulose nanocrystals are important in carbon dioxide production by mitigating climate change. The other studies are mainly related to plant stress (Bahrulolum et al., 2021; Zulfiqar and Ashraf, 2021), toxicity (Shetty et al., 2021) and NP uptake (Avellan et al., 2021; Sarkar et al., 2015). Hence this allows to confirm what was reported in Figure 8: publications about NPs and insects are decreasing, while food security research is not in the ranking (Table 3) because it is still growing.

3.3.3. Keywords Analysis

According to Scopus there are almost 896,000 documents found if “nanoparticle” is used as a keyword, by adding the words “climate change” and “agriculture” in the query only 186 publications are resulted (only 0.2% of the total). This means that nanoparticles are still little studied and applied in the world of agriculture despite the many benefits they can provide. The co-occurrence map, using the keywords of the 186 articles in the Scopus database, revealed the most occurrence index keywords (Figure 6).

The size of the circles is determined by the relevance of the words within the network. The bigger the circles, the bigger the occurrence of the keyword within the addressed data set. It can be seen that together with nanotechnology, agriculture and climate change, many words are closely associated, the most important of which are plant growth, abiotic stress and crops. All keywords were ranked from least to most recent. From Figure 6, it can be seen that the keywords 'agriculture', 'climate change' and 'nanotechnology' are present in the articles between 2021 and 2022. The topics associated with these three keywords are correlated by having a color tending towards yellow, so they are recent in the literature. ‘Agriculture’, ‘climate change’ and ‘nanotechnology’ keywords are very close in the bibliometric analysis, this means that they are strongly related to each other.

Moreover, they are surrounded by big circles suggesting that they are very important topics. From this bibliometric analysis is possible to deduce that ‘agriculture’, ‘climate change’ and ‘nanotechnology’ keywords are linked to plant topics (growth, physiology, biotic and abiotic stress, fertilization, drought), environment topics (heavy metals, ecosystem, salinity, lead, cadmium) and food topics (food safety, yield, food supply). According to Figure 7, it is possible to notice that nanoparticle-related topics have over the past 10 years been increasingly the object of study, all the bar charts show a positive trend. The topic that has experienced the greatest surge is food safety, in fact in 2014 only 1 document had been produced while in 2023 160 documents were published (Figure 7.D). Furthermore, thanks to Figure 8, it can be seen that over time the amount of insect studies related to NPs has decreased (just over 15 percent) while research related to plant growth (more than 50 percent) and food security (about 10 percent) have increased. With regard to food safety, the fact that studies related to it have increased would indicate an increase in hazards in food preservation.

4. Final Remarks and Future Challenges

Rising temperatures and changing rainfall patterns are some of the main effects of climate change, these two main factors can bring other several problems such as stressed plants, weed spreading and spores proliferation during food storage. Moreover, the uncontrolled and excessive use of pesticides and fertilizers in modern agriculture is aggravating this situation. Due to global warming, plants are submitted to new stress, hence nutrient uptake, plant defense and biofortification are favored by NPs. All the studies reported show how microelements are essential for plant development. Through the adoption of nanotechnologies such as nanoparticles, the mitigation of the effects of climate change can be achieved. In fact, through the insertion of macronutrients (N, P, K) and microelements (Fe, Zn, Mg) inside the nanoparticle, it is possible to bring nourishment to the plant in a slow and continuous way avoiding environmental problems such as eutrophication of water.

Moreover the amount of nano-fertilizer required is low, this means a reduction in costs for farmers. Conversely, inserting agrochemical compounds inside the nanoparticles, for the control of insects and weeds, it is possible to carry out a more accurate and effective fight using very small doses of chemical compounds. In this way it is possible to significantly reduce the release of pollutants in the agroecosystem. Furthermore, nanoparticles are important in increasing the shelf life of agricultural products in the trade chain and reducing their perishability. In fact the bibliometric analysis and the search of the main topic related to NPs shows that the research in food safety is increasing exponentially. Therefore, nanoparticles adapted for agricultural needs such as nano-fertilizers, nano-pesticides and nano-emulsions can be a solution in reducing the negative impacts of the agricultural sector on climate change. It is therefore necessary to continue studying the benefits and possible problems of these technologies, improving their functioning and developing other nanotechnological solutions.