2026 Volume 14 Issue 1 Pages 43-67
Global agriculture faces escalating challenges such as land degradation, climate change, water scarcity, and excessive use of agrochemicals, all of which jeopardize food security and compromise sustainable crop productivity. Unsustainable agricultural methods have intensified these problems, resulting in the inefficient utilization of scarce natural resources and diminished resilience of food production systems. In this context, nanobubble technology has emerged as a groundbreaking approach to addressing critical challenges in crop production and ensuring sustainable production through enhancing crop development from the initial germination to later growth stages by promoting nutrient uptake, stimulating growth hormone production, supporting beneficial microbial activity in the rhizosphere, and modifying soil physicochemical properties. These changes primarily result from the molecular and physicochemical modifications induced by nanobubbles. Recent findings further explained that nanobubble-mediated irrigation has also been shown to alleviate both biotic and abiotic stress in crop cultivation. However, the precise mechanisms by which nanobubbles promote plant growth remain incompletely understood. Considering these aspects, this review summarizes i) synthesis methods of nanobubbles ii) recent global research on the application of nanobubbles in agriculture, with a focus on the possible mechanisms by which they enhance crop production, and iii) several key research gaps related to the use of nanobubbles in crop cultivation which highlighting the critical need for future studies to address these limitations.
Global food demand is projected to rise sharply by 2050; FAO estimates agricultural output must increase by about 60% from 2005/07 levels, while some models suggest crop demand could nearly double due to population growth and higher consumption [1]. Around 854 million people (about 14% of the global population) suffer from chronic or acute malnutrition. Although agriculture represents a small share of the global economy, it supports the livelihoods of millions [2]. In 2019, agriculture provided 27% of global employment but only 4% of world GDP [3]. In middle and low-income countries, however, agriculture has a much stronger influence on national GDP and economic stability.
Since the green revolution, agriculture has accelerated environmental degradation. Intensive use of fertilizers, agrochemicals, and plastic mulches has caused extensive pollution, including groundwater contamination and eutrophication [4]. Agriculture is a major greenhouse gas emitter, mainly generated from rice fields and livestock [5]. Historically, from the 1800s to the early 1900s, production increases were prioritized over sustainability [6], which collectively contribute to chemical pollution, global warming, and toxicity, posing risks to humans and wildlife [4].
Nanotechnology has gained significant attention for addressing environmental challenges, with applications in biomedicine, biology, chemistry, agriculture, decontamination, materials science, food technology, and energy [7]; Figure 1. Nanobubbles (NBs), also known as ultrafine bubbles (UFBs), are a major research focus [8]. NBs are nanoscopic gaseous cavities in aqueous solutions that alter water properties [9]. Nanobubbles are classified as surface and bulk NBs; they typically measure under 1 µm in diameter [10]. NBs smaller than 100 nm remain suspended due to Brownian motion, while larger ones rise and collapse rapidly [11]. Their unique properties, such as long retention time, high air solubility, and strong adsorption, result from their small size, large surface area, and high internal pressure [12]; Figure 1. In this regard, zeta potential is commonly used to evaluate NB stability.
NB generation techniques include electrolysis, membrane-based methods, and cavitation [13]. Effective techniques must be efficient, stable, and simple [14]. Each method has advantages and limitations, and developing cost-effective, stable, and scalable approaches for gaseous NB production is essential. While suitable for theoretical and laboratory research, few methods can generate NBs at a rate sufficient for industrial use [15].
In recent years, research on NBs in agriculture has grown significantly due to their potential as a sustainable technology for crop production. However, practical applications remain limited. As a renewable approach, NBs in water can enhance plant growth and development [16], making them valuable for addressing food security challenges. They also support cleaner and more sustainable agricultural systems. This review synthesizes existing literature on NBs, focusing on their impact on crop growth and development, summarizing key findings, and identifying gaps for future research.
To synthesize prior work on NBs in sustainable agriculture, we conducted a bibliometric analysis of NB-related applications, focusing on annual output, leading countries, keyword distributions, and citation networks. Following PRISMA, we executed a three-stage process (Figure 2). We built the dataset from Scopus, Web of Science, and PubMed using the query: (“nanobubble” OR “ultrafine bubble”) AND (“sustainable agriculture” OR “crop production” OR “vegetables” OR “fruits” OR “seed germination” OR “growth promotion” OR “rhizosphere” OR “microbial diversity in soil” OR “gene expression” OR “bubble characteristics” OR “reactive oxygen species” OR “resource utilization”), limited to English-language research articles from 20042024. Initial retrievals were 180 (Scopus), 49 (Web of Science), and 80 (PubMed).
Several inclusive criteria were comprised to enhance methodological consistency and academic relevance:
-The search period was set to last two decades (2004–2024)
-Only peer-reviewed research articles published in English were considered for the analysis
-Highly focused on agriculture or horticultural full-length research articles
Conversely, studies were excluded if they:
2.2 Screening and selection process-Published in other languages
-Related to other scopes such as medicine, chemistry, aquaculture, engineering, etc.
-Consisted of non-peer-reviewed formats, such as editorials, conference abstracts, patents, or opinion papers
-Were unable to access the full text of the article
After removing 121 duplicates, 188 records remained. According to the phase 2 manual screening, we excluded 139 titles unrelated to our scope (primarily medicine, chemistry, aquaculture, and engineering), and obtained 49 studies (43 originals, 6 reviews). VOS viewer v1.6.16 (CWTS, Leiden University) visualized networks, and Microsoft Excel 2010 summarized document types, publication trends, countries, and keywords.
2.3 Number of publicationsA total of 49 documents on NBs and UFBs were included in this bibliometric study. As shown in Figure 3, publications increased gradually from 2016 to 2021, with a slight rise in 2022. The number remained similar in 2022 and 2023, followed by a peak in 2024 with 18 publications, reflecting strong research growth. Nanobubble integration in crop production is still an emerging and highly specialized field; thus, the total annual output in peer-reviewed literature is naturally limited. In niche research domains, even slight increases in annual publications are scientifically meaningful because they indicate growing research interest, expanded application areas, technological advancements, improved measurement techniques, might have contributed and increasing global recognition. Hence, to confirm that one thing causes another, we would need further qualitative research and context-specific investigation.
These publications related to agriculture have been conducted by 21 countries, and 6 met the threshold for inclusion in the collaboration map depicted in Figure 4; China (24), the United States (7), and Japan (6) were the leading contributors, followed by Indonesia (4), Spain (5), and Thailand (3).
Following [17], keywords for clustering were selected by total link strength. Among 728 terms, 23 met the threshold of more than 5 co-occurrences. Top frequencies: “nanobubble” (26), “cultivation” (12), “oxygen” (11), “seed”, “soil”, “water” (9 each), “control study”, “germination”, “crops” (8 each), “dissolved reactive oxygen species” (7). Outliers unrelated to this bibliometric scope, “non-human”, “articles”, and “hydrogen” were excluded (Fig. 5a).
(a)
(b)
(c)
The overlay map (Fig.5b) shows “nanobubble” dominant across years. Blue (2021) clusters on water treatment/oxidation (“water”, “reactive oxygen species”, “oxygen”); green (2022) on agriculture (“soil”, “crops”, “reactive oxygen metabolites”); yellow (~2023) on experimental terms (“seed germination”, “controlled study”, “plant growth”). The density map (Fig.5c) highlights “nanobubble”, “oxygen”, and “cultivation” in yellow, indicating the highest recent density.
Water bubbles can be categorized into macro-bubbles, microbubbles (MBs), and nanobubbles (NBs). Macro-bubbles (diameter 100 μm to 2 mm) burst at the liquid surface, while microbubbles (diameter 1 μm to 100 μm) gradually dissolve as they shrink [18]. “Nanobubbles” or “ultrafine bubbles” are <1 μm in diameter, typically range from 50-200 nm, and are classified as “bulk” (gaseous cavities in solution) and “surface” (gaseous caps at solid-liquid interfaces) NBs [19]. NBs exhibit unique traits, such as small size, negative surface charge, long-term stability, dominance of Brownian motion, and high internal pressure. These properties enable high zeta potential, enhanced adsorption, hydrophobic interactions, ROS generation, and improved gas-liquid mass transfer [14, 19].
3.1 Persistence and stabilityNanobubbles exhibit exceptional longevity, persisting for weeks or months compared to the short lifespan of microbubbles [20]. Their high specific surface area enhances mass transfer and gas solubility [21]. NB stability is mainly attributed to electrostatic repulsion, supported by hydrogen bonding, dynamic equilibrium, and interfacial skin models. Preferential anion adsorption at the interface generates repulsive forces that counteract surface tension, maintaining bubble size and limiting gas diffusion [21]. Low buoyancy and the formation of a negatively charged electric double layer further reduce gas dissolution and extend NB lifetime [15].
3.2 Zeta potentialZeta potential (ZP) is a key determinant of NB stability in aqueous systems, with higher absolute values indicating greater colloidal stability and longer lifetimes of micro and nanobubbles [14]. The negative ZP of NBs originates from preferential hydroxyl ion adsorption at the gas-water interface, which governs NB charging mechanisms [18]. Increased electrostatic repulsion enhances stability, whereas low ZP promotes coagulation. NBs exhibit negative ZP across pH 4–12, ranging from -4.3 to -62 mV and approximately -20 to -30 mV at neutral pH [15]. This negative charge is attributed to the lower hydration energy of hydroxyl ions compared to hydrogen ions, favouring their presence at the interface [21].
3.3 Mass transfer propertiesMass transfer is a crucial component of a system that typically determines the efficiency of a technique in various gas-liquid phase processes. The bubbles’ size distribution, increasing velocity, gas-liquid hydrodynamics, coalescence, break-up surface to volume ratio, and physical characteristics significantly affect the mass transfer efficiency [22].
3.4 Free radical generation by bubbles collapsingNanobubbles can generate ROS, enabling effective sanitization [21]. ROS formation is primarily driven by NB collapse, which releases substantial surface energy that excites electrons and promotes the splitting of water molecules [14]. Due to their high internal pressure, NBs release greater surface energy, facilitating the conversion of oxygen into ROS [21]. These properties have led to the application of NB technology in agriculture, medicine and biomedicine, food science, environmental engineering, and water reclamation [19].
Although nanobubble collapse is a well-known procedure to generate ROS through rapid energy release, quantitative ROS yield varies considerably with experimental conditions, dissolved oxygen concentration, surfactant content, bubble size, and measurement technique. Therefore, standardized numerical ROS outputs remain difficult to generalize across studies, particularly for food and environmental engineering applications. In addition, previous studies have confirmed ROS formation from NB collapse using ESR spectroscopy and electrochemical oxidation techniques, demonstrating mechanistic viability without requiring absolute yield comparison [23, 24].
Recent agricultural research has focused on the impact of NBs on crop production, especially during key growth stages. Studies show NBs promote seed germination in tomatoes [25], barley [10], red mustard [26], Gmelina [16], and spinach [27]. Nanobubbles also enhance plant growth in NB-treated musk melon, which showed increased stem length, diameter, and leaf number [13], while tomato seedlings showed better elongation, leaf thickness, and stem growth, but no significant improvement in net assimilation rate [28]. Similarly, lettuce treated with microbubbles had 2.1 and 1.7 times higher fresh and dry weights than macro bubble-treated plants [29]. Nanobubble-treated Brassica campestris showed significant gains in fresh weight and leaf length. UFBs promoted lettuce growth, but high concentrations could limit it [10]. Nanobubbles also impacted rice root growth and tillering capacity [30, 31], and NB-containing water stimulated tomato and lettuce growth in soils affected by bacterial wilt and repeated cultivation [25]. Overall, NBs boost crop yields through these changes [13, 30]. Table 1 summarizes the latest findings on nanobubbles in crop production.
| Crop | Type of nanobubble | Size of nanobubble | Key findings | Reference |
|---|---|---|---|---|
| Rice (Oryza sativa L.) | - | 167.2 nm |
Enhanced the primary and crown root lengths Increased the elongation rate of the primary root |
[31] |
| ONBs | 700 nm–12 µm |
Enhanced the yield by nearly 4%–15%. Increased the tiller-bearing rate Amplified the SPAD and Pn values of the flag leaves |
[32] | |
| ONBs | 216.7 nm and 207.2 nm |
Enhanced the root elongation and plant height in rice seedlings Increased the yield by almost 8% when using a similar level of fertilizer as the controls |
[13] | |
| ONBs | - | Increased arsenite oxidation and arsenate adsorbed on crystalline iron oxides | [33] | |
| MNBs | 700 nm–12 µm |
Increased the final number of tillers per hectare by 94.1% Enhanced the nitrogen accumulation by 10.79% at the tillering stage Increased the yield of early rice by 97.08% |
[30] | |
| Tomato (Solanum lycopersicum) | - | - | Increased yield by 18.94%, CO2 emission by 10.72% and N2O emission by 29.76% | [34] |
| - | - |
The germination rate was nearly 55% in damaged soil Improved the crop growth in the soil damaged by a bacterial wilt-like disease |
[24] | |
| ONBs | <1000 nm |
Increased the yield by 23% Enhanced the activities of carbon-cycling enzymes, nitrogen-cycling enzymes, and phosphorus-cycling enzymes Augmented the microbial biomass carbon concentration by 26% |
[35] | |
| OMBs | 136.2 nm |
Increased the above-ground and underground dry matter by 13.89-34.31% and 9.33–22.21% Augmented vitamin C content by 6.55-61.41% Enhanced the lycopene content by 16.16–55.37% Increased the total soluble solids and soluble sugar contents by 2.99–21.98% and 4.36–30.3% Increased soil urease content in the rhizosphere by 1.29–35.43% and hydrogen peroxide content by 12.35–55% |
[36] | |
| - | - | Increased both leaf area, leaf thickness, relative growth rate, net assimilation rate, and aboveground dry weight | [28] | |
| NBs | - |
Increased the yield by 23% Enhanced the enzymatic activities, soil microbial biomass, and plant-available phosphorus content |
[35] | |
| ONBs | - |
Improved the root distribution Increased the nitrogen and water uptake efficiency |
[37] | |
| HNBs | - | Increased the concentrations of carotenoids, flavonoids, and resveratrol by 10% | [38] | |
| NBs | - | Enhanced the yield, soluble sugar, and vitamin C content | [39] | |
| NBs | - | Increased the soil’s available nitrogen and phosphorus concentration and yield | [40] | |
| ONBs | - | Enhanced soil microbial community, structure, and permeability | [41] | |
| CNBs | - |
Boosted seed germination by approximately 20% Increased plant height and number of leaves |
[42] | |
| Cherry tomato (Lycopersicon esculentum var. cerasiforme) | HNBs | - | Increased the yield, soil available nitrogen, phosphorus, and potassium content | [43] |
| Muskmelon (Cucumis melo) | HNBs and ONBs | - |
Increased melon seed germination, seedling growth, and enhanced root development Reduced aphid damage through enhancing trichome density in leaves and petioles |
[44] |
| ANBs | - | Promoted the growth of stem length and diameter, leaf number, and leaf width. Increased the germination rate by 90% | [7] | |
| Soybean (Glycine max) | - | 215 nm | Reduced the osmotic/drought stress | [45] |
| Radish (Raphanus sativus L.) | ONBs | - | Increased root length and fresh weight | [26] |
| NBs | - | Increased the rate of seed germination and uptake of water by seeds | [46] | |
| Lettuce (Lactuca sativa) | - | - | The germination rate was 60% in damaged soil | [24] |
| - | - | Increased shoot fresh weight, total leaf area, and total antioxidant content | [29] | |
| ONBs | - | Reduced the membrane leakage and osmotic potential in the roots and leaves | [47] | |
| ONBs | - | Increased the net photosynthetic rate, intercellular carbon dioxide concentration, and yield | [48] | |
| ANBs | - | Enhanced the germination rate | [49] | |
| Cucumber (Cucumis sativus) | ONBs | 136.2 nm |
Enhanced the above-ground and underground dry matter content by 16.69–33.87% and 16.53–21.79%, respectively Increased vitamin C content by 6.72–58.85% TSS and SS contents were increased by 6.48–39.27% and 2.56–44.57% Increased soil urease content in the rhizosphere by 1.29–35.43% and hydrogen peroxide content by 12.35–55% |
[36] |
| Barley (Hordeum vulgare) | ONBs | - |
Enhanced the germination rate Increased the fresh and dry weight of the shoot and root |
[26] |
| - | - | Enhanced the seed germination | [10] | |
| HNBs | Enhanced antioxidant activities and removed cytotoxic reactive oxygen radicals | [50] | ||
| Air UFBs | - | The highest concentration induced earlier seed germination | [10] | |
| Wheat (Triticum aestivum) | ONBs | - | Increased root length and fresh weight | [26] |
| Red mustard (Brassica juncea L.) | ONBs | - |
Boosted the germination rate Enhanced the fresh and dry weight of the shoot and root |
[26] |
| Pak choi (Brassica campestris) | ONBs | - | Increased shoot fresh weight and plant height | [26] |
| Gmelina (Gmelina aborea) | - | - | Increased the germination potential by 80%, germination rate by 6.65% day-1, and germination value by 6.29 | [16] |
| True shallot (Allium cepa var. ascalonicum) | - | - | Increased the germination rate and radicle emergence to more than 80% | |
| Bean (Phaseolus vulgaris) | - | 200 | Enhanced the germination rate | [51] |
| Fava bean (Vicia faba) | ANBs, | - | Inhibited the growth of the stem length | [26] |
| Strawberry (Fragaria × ananassa Duch.) | HNBs | - | Enhanced the flavour components and aroma in fruit | [52] |
| Delayed the degradation and extended shelf life | [53] | |||
| Enhanced the volatile profiles, sugar-acid ratio, and sensory attributes | [54] | |||
| Chinese cabbage (Brassica chinensis L.) | HNBs | 300 | Increased the plant weight, height, maximum leaf length, width, nutritional value, and yield | [55] |
| Spinach (Spinacia oleracea L.) | - | - | Increased the germination rate and sprout growth | [27] |
| Aromatic coconut (Cocos nucifera Linn.) | O3 UFBs | - |
Controlled the microbial growth and the surface browning of the trimmed coconuts Decreased the concentration of citric acid and NaCl by approximately 25% |
[56] |
| Carnation (Dianthus caryophyllus L.) | HNBs | - | Delayed the petal senescence and prolonged the vase life | [57] |
| Microbubbles (MBs), Nanobubbles (NBs), Air Nanobubbles (ANBs), Oxygen Nanobubbles (ONBs), Carbon dioxide Nanobubbles (CNBs), Nitrogen Nanobubbles (NNBs), Oxygen Microbubbles (OMBs) | ||||
Nanobubbles enhance crop quality by improving photosynthetic pigment levels and biochemical composition. For instance, UFB with hydrogen and oxygen increased chlorophyll content and photosynthesis in melons, leading to greater fruit weight [44]. Moreover, NB-treated tomatoes also showed higher chlorophyll, boosting photosynthetic rates, and biomass [35]. Furthermore, oxygen microbubbles increased antioxidants and vitamin C in tomatoes [29, 36, 38, 58] while hydrogen nanobubbles improved strawberry flavor [52].
Excessive agricultural inputs cause environmental issues and raise costs [13]. Nanobubble irrigation is a sustainable approach, boosting crop performance and fertilizer use efficiency [39]. For example, NBs improved nutrient uptake in rice, reducing fertilizer needs by 25% [13]. In addition, Hung et al. [44] observed that UFB controls pests and reduces postharvest losses through delaying senescence in cut carnations. Figure 6 illustrates the overall impact of nanobubble-contained irrigation on crops.
Nanobubble irrigated agriculture works via physicochemical and physiological mechanisms. NBs increase oxygen dissolution and availability due to high internal pressure and a large interfacial area. Dissolved oxygen boosts root respiration, elongation, and nutrient transport, increasing root biomass and growth in crops like rice and tomato [10, 28, 33].
Nanobubble collapse produces ROS, acting as signaling molecules that regulate seed germination, cell division, and stress adaptation. This explains improved germination, seedling vigor, and photosynthetic pigment retention in lettuce and melons [44, 48]. Moreover, ROS signaling enhances metabolic activity and secondary metabolite synthesis, correlating with better fruit quality, antioxidants, and aroma in strawberries [52] and tomatoes [36].
On the other hand, NBs modify nutrient bioavailability by altering redox conditions and the soil-root interface. Improved oxygenation enhances microbial nitrification, converting ammonium (NH4+) to more easily assimilated nitrate (NO3-). This explains higher fertilizer use efficiency and reduced requirements in rice and lettuce [13, 29]. Simultaneously, oxygenated NB water promotes healthier soil by balancing rhizosphere microbes and overwhelming anaerobic pathogens [25, 44].
4.3 Growth promotion versus growth inhibitionPlant responses to NBs are not always linear, varying with NB concentration, gas type, and environment. Low-to-moderate NB concentrations are beneficial; elevated dissolved oxygen, enhanced microbial activity, and nutrient availability stimulate root metabolism and photosynthetic efficiency [13]. Conversely, high NB densities may cause oxidative stress, membrane destabilization, or nutrient imbalance due to excessive ROS or microbial disruption [10, 45, 59].
Inter-study variability is significantly attributable to the gas type used for NB generation. For instance, oxygen-nanobubbles (ONBs) primarily enhance dissolved oxygen, supporting aerobic microbes and nutrient mineralization. Conversely, air nanobubbles (ANBs) and carbon dioxide nanobubbles (CNBs) may create differing redox environments, pH, or gas exchange dynamics, potentially limiting growth at high doses. Thus, gas composition is key to NB’s stimulatory or inhibitory effects. Differences in crop species, variety, growth stage, and cultivation method also explain variability [29, 32]. In this regard, high oxygen-demand crops benefit more from ONBs, especially in poor conditions. Slow-growing species may be more sensitive to high ROS from elevated NB densities. Adilaksono et al. [29] also found that higher UFB content in water boosted growth, but the effect was variety-dependent. Furthermore, the growing condition (hydroponic vs soil) influences results due to varying oxygen diffusion and microbial dynamics. Hence, these comparative observations reconcile inter-study variability and indicate that NB application is dosage-specific rather than universally beneficial.
4.4 Nanobubbles containing water application under stress ecologiesIn addition to the above-mentioned scenarios, NBs containing water irrigation have been tested in stress conditions, which received increased interest due to their potential to promote soil moisture retention and plant development. In this regard, few studies have been conducted to investigate heavy metal stress and other inorganic substances’ stress mediated by NBs. The key findings of these studies are summarized in Table 2.
| Crop | Stress condition | Nanobubble size (nm) | Key findings | Reference |
|---|---|---|---|---|
| Soybean (Glycine max) |
Low and high-nutrition levels for 8 days |
226 | UFB water enhanced growth significantly under nutrient deficit stress, but showed no improvement or negative effects under favourable growth conditions | [60] |
| Induced osmotic stress through polyethylene glycol 6000 (PEG6000) for 9 days | 215 |
Reduced superoxide radicals through UFB Increased the shoot biomass after UFB treatment |
[45] | |
| Coffee (Coffea arabica) | Repeated drought stress over 3 years | 215 |
Increased the root length and surface area Inhibited leaf senescence under drought conditions |
[61] |
| Wheat (Triticum aestivum) |
Induced zinc oxide nanoparticle stress by 500 mg L−1 solution |
74 |
Improved the growth and nutrient status of wheat Increased the capability of soil oxygen input, leading to increased root activity and glycolysis efficiency in roots |
[62] |
| Radish (Raphanus sativus L.) | 20 ppm concentration of Cd2+ ions | - | Alleviated the stress effect of Cd2+ on radish seed germination | [63] |
Maintaining growing substrate properties is crucial for crop productivity. The oxygen nanobubble (ONB) treatments enhance soil water retention in micropores by increasing porosity and connectivity. For example, Sha et al. [33] showed that ONBs significantly improve dissolved oxygen and redox potential (Eh) in paddy soil, promoting aeration and protective iron plaque formation, which reduces arsenic mobility [64]. Similarly, ONBs also modify soil structure, driven by microbial activity, reducing large aggregates while increasing smaller ones. This accelerates organic carbon decomposition, improving soil permeability, water retention, and nutrient distribution [65, 66]. Carbon dioxide NBs lower soil pH, while ONBs stimulate ROS production, enhancing redox potential but potentially causing oxidative stress if uncontrolled [67].
Coordinated cellular processes like cell division, expansion, and differentiation drive plant growth. NB treatments enhance the expression of genes involved in cell division, such as the MCM complex and DNA replication [68]. Fine bubble implosion generates hydroxyl radicals, which promote these effects [22]. Hydroxide radicals enhance the expression of nutrient absorption genes and enzymes, thereby improving plant physiology [69]. Wang et al. [13] studied rice gene expression in response to NBs and found increased expression of genes related to antioxidant production, nutrient transporter and reservoir activities, and metallochaperone activity. In particular, SKOR, PiT-1, and OsBT genes, involved in nitrogen (N), phosphorus (P), and potassium (K) uptake, showed significantly higher expression in NB-treated rice roots [13]. Li et al. [43] reported that hydrogen nanobubble water (HNW) increased transcription of NPK absorption genes in tomato, including NRT2.3, NiR, ARE1, NLP4, and AKT1. This study further found that NPK transport-related genes (e.g., LeAMT2, LePT2, SlHKT1,1) were positively correlated with soil NPK reduction and fruit yield, demonstrating that fine bubbles improved gene expression and nutrient transfer, leading to a 9.1% yield improvement in cherry tomatoes grown without fertilizer.
Growth hormone levels and genetic responses to environmental factors (e.g., temperature, nutrition) significantly affect plant growth. For instance, Wang et al. [13] found that low and high-frequency NB treatments increased gibberellin concentrations in rice roots compared to controls. Simultaneously, levels of GA3, GA4, and GA7 were higher in both NB-treated groups. NBs also triggered biological pathways related to energy metabolism, signal transduction, and environmental adaptation. For example, KS and KO gene expression were significantly elevated in NB-treated rice, suggesting that NBs enhance growth by initiating GA hormone synthesis. Thus, NB water increased root elongation and plant height, likely by boosting the expression of growth-related genes and promoting gibberellin production [13].
In addition, barley was also studied for gene expression during NB treatments [68]. Several genes associated with cell division, such as the MCM complex, DNA replication, and cell proliferation, exhibit increased expression during the NB treatment. Expansions, xyloglucan endotransglucosylase/hydrases, peroxidases, and lipid transfer proteins are some of the proteins that affect cell wall loosening. Liu et al. [68] revealed that seed embryos submerged in NB water expressed higher levels of these proteins. These findings suggest that NB water can stimulate cell division and expansion of gene expression. Moreover, gene expression for NADPH and peroxidase was induced by NB water. For instance, Hung et al. [44] focused on the gene expression of melon due to UFB treatments. The results showed that NBs stimulated root growth by regulating the heme oxygenase-1 and carbon monoxide pathways.
Furthermore, UFB can induce jasmonic acid (JA) biosynthesis genes. According to the activation of JA production genes, the JA accumulation would increase in the plants. In addition, the application of hydrogen nanobubble water enhanced the lycopene content in tomatoes, supported by the upregulation of SlPSY1 and SlPDS transcripts (lycopene synthesis genes). Therefore, it was suggested that the two genes mentioned above might be the target genes responsible for hydrogen nanobubble water-triggered lycopene accumulation [43].
NBs enhance rice development and resilience to environmental stress by increasing the expression of important genes and stimulating plant hormone production, ultimately boosting crop yield [13]. The increased expression of nutrient absorption genes and hydroxyl radicals improves nutrient efficiency. For example, Wang et al. [13] showed that using 25% less fertilizer with fine bubbles resulted in similar yields to traditional cultivation. In addition, Zhao et al. [52] found that hydrogen nanobubble water regulated the expression of metal transport genes (e.g., Nramp5, HMA2, HMA3, IRT1, LCD) in rice, reducing Cd accumulation. Moreover, Lv et al. [63] observed that under Cd²⁺ stress, hydrogen NB water reduced gene expression changes during seed germination, alleviating Cd-induced effects. Figure 7 illustrates the ROS-mediated gene expression in crops.
Nanobubble generation produces ROS, including superoxide anion (O2⁻•), hydroxyl radical (•OH), hydrogen peroxide (H2O2), and singlet oxygen (¹O2) [45, 68]. Nanobubbles disrupt the hydrogen-bonding network in water, potentially affecting physiology and bioelectric fields [70]. Nanobubble collapse generates hydroxyl radicals, promoting cellular development [27]. Exogenous ROS from NB water enhances endogenous plant ROS [27], which act as secondary messengers in stress tolerance [71]. However, ROS balance is crucial; low to moderate levels signal growth, while excess results in oxidative stress and damage [29, 68, 72].
7.1 Plant growth hormone relationship with ROSKey plant hormones regulate root development [73, 74, 75, 76]. Recent studies classify ROS as crucial hormone-like signaling molecules, essential for balancing cell differentiation and proliferation [77]. While excessive ROS can cause cellular damage, potentially leading to plant death [77]. Low levels of ROS are vital for root development under normal conditions [78] and modify the cell wall via lignification. Endogenous ROS are generated in roots, primarily by mitochondrial or plastid respiration and NADPH oxidases (RBOHs) [79, 80, 81].
Hydroxyl radicals are involved in auxin-induced cell expansion, contributing to cell wall lignification, stiffness, and elongation based on auxin levels [82]. Herein, ROS also modulate auxin signaling by influencing auxin-responsive gene expression and PIN-FORMED (PIN) protein activity, regulating root hair formation, lateral root initiation, and apical dominance [83]. In this context, ROS controls the size and redox status of the meristematic zone by regulating the cell cycle [77], with some ROS promoting cortex cell proliferation [84]. The ROS homeostasis at the root tip is crucial for elongation and differentiation [77]. Specifically, superoxide radicals in the meristematic zone and H2O2 in the elongation zone regulate genes like UPB1 with mutations (e.g., UPB1-1) that cause an extended root phenotype [85]. Simultaneously, UPB1-mediated ROS regulation is also key to lateral root development [77].
Exogenous application of ROS, particularly H2O2, influences root growth. For instance, Deng et al. [86] found that low H2O2 concentrations enhanced root weight, number, length, and surface area in sweet potato, promoting adventitious root formation and stimulating cell expansion in the elongation zone. However, higher concentrations impaired root performance. In summary, ROS have a dual role, whereas moderate levels are crucial signaling molecules for root growth and hormone signaling, while excessive accumulation is harmful, highlighting the importance of ROS balance for optimizing plant growth.
7.2 ROS-mediated cell wall looseningHydroxyl radicals are crucial mediators of cell wall loosening, a process vital for cell elongation and root growth. During seed germination and early development, hydroxyl radicals are generated within cell walls, contributing to endosperm weakening and facilitating radicle elongation [87]. Cell wall loosening is necessary for radicle elongation, which is driven by water uptake, and for weakening restrictive seed coat structures [88]. Thus, hydroxyl radicals’ in vivo attack on cell wall polysaccharides is a key regulatory mechanism for various developmental processes.
At the molecular level, hydroxyl radicals are highly reactive, non-enzymatic mediators that cleave glycosidic bonds in cell wall polysaccharides. Previous studies show apoplastic hydroxyl radicals from Fenton-type reactions induce scission of cellulose and hemicellulose (xyloglucans), rapidly decreasing wall tensile strength and increasing extensibility [89, 90]. Additionally, ROS interacts with pectin chemistry, modulating dimethyl esterification and Ca²⁺ions-mediated cross-linking, which regulates wall stiffness [91]. This non-enzymatic cleavage and pectin remodeling mechanistically explain hydroxyl radicals-mediated cell wall loosening during radicle emergence and early root growth.
7.3 Relationship between nanobubbles and dissolved oxygen contentNanobubble oxygen increases dissolved oxygen (DO) concentrations [92]. Elevated DO promotes microbial decomposition of organic matter into plant-available nutrients [66]. Oxygen is critical for nutrient transport, and higher availability enhances absorption, supporting root metabolic processes and overall plant growth [93]. For example, a study using fine bubble technology (FBT) aeration in aquaponics increased DO to 9.31 mgL-1. This rise, attributed to enhanced nitrifying bacteria activity, resulted in higher nitrate concentrations and a 35% increase in total crop yield [19].
Root hypoxia (insufficient oxygen) weakens root respiration by shifting metabolism to anaerobic pathways, reducing root growth, ion transport, and fluid flow [93]. Nanobubbles root growth by improving oxygen availability and modifying the root zone microenvironment. These favorable aerobic conditions stimulate microbial activity, collectively enhancing root morphology and nutrient uptake. Previous studies link NB growth promotion to increased DO concentration in growing media [94, 95].
Despite the positive effects of increased DO levels, some studies suggest that excessive oxygen availability does not necessarily translate to better crop performance. For example, a study on maize reported that plants exposed to DO concentrations of 10, 20, and 30 mgL⁻¹ exhibited the highest root growth and yield at a moderate DO concentration of 20 mgL⁻¹ [39].
Nanobubbles enhance soil microbial activity, diversity, and community composition by increasing nutrient availability and oxygen content [35, 96]. Soil microbes are crucial for improving nutrient absorption and promoting plant growth [34]. They are key producers of extracellular enzymes and are important for nutrient cycling [35, 39]. Micro-nanobubbles (MNBs) improve the feedback between soil fertility and microorganisms, increasing the number, activity, and function of bacteria involved in nitrification and nitrogen fixation [32]. Aerobic conditions created by oxygen-rich irrigation promote aerobic microbes [39]. Increased soil aeration boosts microbial biomass and alters community composition, confirming improved microbial diversity [35]. Nanobubble oxygen (NBO2) increased soil bacterial richness and diversity, altering composition by increasing aerobic or facultative bacteria (e.g., Gaiellales, Sphingomonas, Devosia) and reducing anaerobic Steroidobacteraceae abundance [41].
Soil enzymes and active organic components indicate soil quality, fertility, and organic matter dynamics [39]. Nanobubble treatment boosts soil enzyme activity by stimulating microbial growth and increasing extracellular enzyme organo-complex activity. Fluctuations in microbial diversity cause enzyme activity changes [35]. Moreover, Zhou et al. [39] showed that micro-nanobubble oxygen (MNBO) application increased soil urease, phosphatase, and catalase content by accelerating root exudates and microbial activities. Increased enzyme activities reflect and promote microbial activity, raising nutrient accessibility for plants [35].
Micro-nanobubble oxygen application increased soil phospholipid fatty acid concentration, creating a favorable microbial environment due to enhanced soil permeability and root growth. Roots secrete metabolites (sugars, fatty acids), enhancing microbial-root interactions [39]. Certain ROS (e.g., hydroxyl radicals) have strong disinfection properties [97]. For example, UFB water improved the Solanum lycopersicum growth in soil damaged by bacterial wilt and encouraged Lactuca sativa establishment in soil harmed by repeated cropping [25]. This suggests NBs control harmful microorganisms, benefiting plant health.
Nanobubbles have a high zeta potential, which facilitates plant ion transport. Fine bubbles enhance seed germination by increasing the availability of numerous ions (e.g., K⁺, Na⁺, and Cl⁻) supporting physiological processes like enzyme activation [22, 69]. The high zeta potential promotes ion adsorption and colloidal stability, ensuring even distribution of positively charged nutrients like calcium and potassium [98]. It also contributes to a negative hydrophobic interaction with water [99], reducing water surface tension and improving nutrient absorption efficiency by roots [13]. However, NB effects vary by soil type: air NB-saturated water moderately influenced nutrient retention in silty and sandy loam soils but had no significant effect on clay soil [100].
The hydrophobic characteristics of bulk NBs reduce water’s surface tension, aiding in the release of organic matter and nutrients from soil. Biological decomposition, which relies on soil moisture and oxygen, releases plant-available nutrients like nitrogen (N) and phosphorus (P). NBs supply both water and oxygen, increasing the availability of N and P to plants. Additionally, organic fertilizers high in nitrogen release NH₄⁺ during aerobic biodegradation. The nitrification process converts NH₄⁺ to plant-available NO₃⁻, with NBs providing essential oxygen. Due to their low buoyancy and long lifespan, NBs can sustainably supply oxygen for organic fertilizer mineralization by gently dissolving air or oxygen into the soil's interstitial water, enhancing N availability for plant growth.
Nanobubble application is not always beneficial and can cause several dose-dependent negative effects. It is a well-known process that ROS production occurs throughout the NB synthesis process. Generally, the concentration of ROS would be proportional to the NB density [27]. Therefore, with higher concentrations of NBs, certain crop species showed poor growth performances. For instance, Liu et al. [27] observed that at higher NB concentration, radicle elongation and chlorophyll formation in carrot seedlings became reduced. This might be due to ROS-mediated oxidative stress, which could damage roots, root hairs, and sensitive rhizosphere biota if overdosed in soil systems. According to the results of Yan et al. [59], Cd, like toxic metals, can be bioaccumulated with NB treatment, which finally results in serious health hazards.
In addition, NB treatments can modify soil physical and chemical conditions in ways that could be stressful to soil biota. For example, irrigation of ONBs has been reported to increase electric conductivity (EC), organic matter decomposition, and soil compaction in organic-rich soils [101]. These alterations in microbial diversity and function pose a potential long-term risk to soil ecological stability. The same study further explained that ONB treatment increases the leaching of several heavy metals (e.g., Cu²⁺ and Mn²⁺), which creates a biological threat. Zhou et al. [66] also found that NB water drip irrigation significantly abridged the diversity of rhizosphere microorganisms. The authors further explained that changes in the soil physiochemical properties (e.g., pH, redox gradients, EC etc.) after NB irrigation might be the reason for diversity retardation. This microbial hindrance would negatively impact the soil nutrient cycles.
Given their unique physicochemical properties and demonstrated efficacy, NBs hold substantial promise in transforming agricultural practices. Their integration into farming systems has the potential to enhance productivity, resource-use efficiency, and environmental sustainability significantly. Thus, we suggest the following key areas to explore scientifically in the future.
• Coupling nanobubble technology with sensor-based automation may enable precise, real-time delivery of NB-enriched water under diverse conditions; however, its application remains largely confined to laboratory and pilot-scale studies. Therefore, future research must focus on developing scalable NB delivery systems, especially for field-based irrigation networks and hydroponic cultivation platforms.
• Equally important is a comprehensive techno-economic analysis to assess the cost-effectiveness and financial feasibility of NB technology for farmers across diverse agricultural settings.
• To broaden the applicability of NBs, it is imperative to expand research across a wider spectrum of crop species, which aids in the understanding of crop-specific NB interactions.
• Investigations should also prioritize the identification of optimal gas types (e.g., O2, O3, N2, CO2) and their concentrations tailored to particular crops, growth stages, and soil environments.
• An often-overlooked aspect is the influence of NBs on rhizosphere microbial communities, plant health, and nutrient uptake efficiency. Elucidating these interactions could offer critical insights into how NBs modulate biological processes and enhance plant performance.
• While preliminary studies have revealed changes in gene expression in plants exposed to NBs, the broader genomic and proteomic responses remain largely unexplored.
• There is also a critical need for mechanistic studies at the cellular level to determine whether NBs interact directly with plant cells, alter membrane permeability, or exert effects through extracellular signaling pathways.
• Further research on interactions between nanobubbles and agrochemicals may allow reduced chemical use without yield loss. Evidence also shows that nanobubbles alone can exert pesticidal effects, as reported in cucumber crops, indicating their potential as a biocompatible pest control strategy. Overall, a systematic assessment of nanobubble technology for lowering water, fertilizer, and pesticide inputs while sustaining or enhancing yields is essential for sustainable intensification.
Addressing these multidimensional research gaps will be instrumental in unlocking the full agronomic potential of nanobubbles and integrating this emerging technology into the future of climate-resilient and resource-efficient agriculture. The key future research directions are summarized in Figure 8.
This review highlights the significant potential of NBs in promoting sustainable agriculture. Bibliometric analysis indicates that NB applications in crop production are a rapidly expanding research area. NB technology can reduce chemical fertilizer and pesticide inputs, improve irrigation efficiency, seed germination, crop growth, and rhizosphere activity due to its inherent characteristics of bubbles. Importantly, this review synthesizes NB physicochemical properties with plant, soil, and rhizosphere responses, providing an integrated understanding of how NB-induced oxygenation and reactive species influence crop performance in a dose-dependent manner. NBs also enhance plant resilience and economic viability, particularly under stress conditions such as drought, as evidenced by improved root traits in crops like rice. These findings suggest that NB technology offers a promising pathway toward cleaner and more resilient food production systems, while highlighting the need for further research on molecular, physiological, and soil-microbial mechanisms, as well as optimized application strategies.
