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Article

Differential Responses of Spinach Cultivars to Micro-Nanoplastic Stress Under Hydroponic and Soil Cultivation Conditions

by
Jinxiu Song
1,2,
Rong Zhang
1,
Xiaotong Bao
1,
Fang Ji
3,
Zhiyu Zuo
1,* and
Wei Geng
4,*
1
College of Agricultural Engineering, Jiangsu University, Xuefu Rd. No. 301, Jingkou District, Zhenjiang 212013, China
2
Key Laboratory of Desert-Oasis Crop Physiology, Ecology and Cultivation, MOARA, Urumqi 830091, China
3
College of Water Resources & Civil Engineering, China Agricultural University, Beijing 100083, China
4
Jilin Academy of Vegetable and Flower Sciences, Changchun 130119, China
*
Authors to whom correspondence should be addressed.
Horticulturae 2025, 11(9), 1062; https://doi.org/10.3390/horticulturae11091062
Submission received: 4 August 2025 / Revised: 21 August 2025 / Accepted: 3 September 2025 / Published: 4 September 2025
(This article belongs to the Section Vegetable Production Systems)
Browse Figures
Versions Notes

Abstract

To investigate the effects of micro-nanoplastics (MNPs) on spinach seed germination and sprout growth, this study employed polyvinyl chloride micro-nanoplastics (PVC-MNPs) as the treatment factor. Six concentration gradients were established under two cultivation conditions—hydroponic and soil. Two spinach cultivars grown in different seasons—the winter cultivar cv. xinbofeit and the autumn cultivar cv. connaught—were evaluated for germination characteristics, sprout morphology, and antioxidant capacity. Results indicated that low to moderate PVC-MNP concentration (1–100 mg/L in hydroponics or 0.1–1.0% in soil) moderately promoted seed germination and seedling growth, with cv. Xinbofeit exhibiting stronger stress tolerance. Conversely, high concentrations (200 mg/L in hydroponic or 2.0% in soil) inhibited germination and root development in both cultivars and induced oxidative stress responses. Principal component analysis identified germination rate, superoxide dismutase (SOD), and peroxidase (POD) activities as key response indicators. Significant inter-cultivar differences and cultivation method dependencies were observed: cv. xinbofeit showed higher sensitivity to elevated PVC-MNPs level, whereas cv. connaught demonstrated greater overall stress resistance. This study demonstrates that micro-nanoplastics exert a dual effect on spinach seed germination and sprout growth, with low to moderate concentrations promoting growth, while high concentrations inhibit development and induce oxidative stress. Moreover, significant differences in response were observed among different cultivars, highlighting the complex risks of micro-nanoplastics in agricultural ecosystems and their cultivar-dependent impacts.

1. Introduction

In recent years, the global surge in plastic production and consumption has intensified concerns regarding the environmental fate of plastic waste. A considerable proportion of agricultural and industrial plastics undergo degradation through weathering, ultraviolet (UV) radiation, and mechanical fragmentation [1,2], eventually breaking down into microplastics (MPs, <5 mm in diameter) and further into nanoplastics (NPs, <1 μm) [3]. These smaller and more reactive micro-nanoplastics (MNPs) exhibit strong adsorption capacity and high mobility [4,5], and have been widely detected in various environmental matrices such as soil, water, and air, making them an emerging class of environmental contaminants [6,7].
Compared to aquatic ecosystems, the distribution patterns, phytotoxicity, and interference mechanisms of MNPs within agroecosystems remain largely underexplored [8,9]. Recent studies suggest that agricultural practices—including the disposal of greenhouse films, degradation of plastic mulches, and irrigation with wastewater—may significantly contribute to the accumulation of MNPs in arable soils [10,11,12]. These contaminants can alter soil physicochemical properties [13,14], reshape microbial community structures [15,16], and negatively impact crop growth and development [17,18]. The magnitude and nature of such effects are influenced by multiple factors, including MNPs type, particle size, concentration, surface characteristics, and environmental context [16,19]. Notably, smaller-sized MNPs are more likely to be absorbed by plant roots and translocated to aerial parts. Nanoplastics, in particular, can penetrate plant cell walls more easily than microplastics, thereby inducing stronger oxidative stress and metabolic disruptions [20]. While low concentrations of MNPs have occasionally been reported to stimulate plant growth, high concentrations generally inhibit seed germination, root elongation, and biomass accumulation [21,22]. Surface properties—such as surface charge, degree of aging, and morphology—also influence their adsorption, uptake, and toxicity, with spherical particles being more readily absorbed by plant roots [23,24].
Once inside plant tissues, MNPs may disrupt seed germination and seedling development by obstructing water and gas exchange, damaging cell membrane integrity, and inducing excessive reactive oxygen species (ROS) production [3,25]. The germination stage is a critical starting point in the plant life cycle and is highly sensitive to environmental stressors [26,27], with direct implications for subsequent growth and development [28,29]. Studies have shown that MNPs can inhibit seed germination and root development by reducing root tip activity and mitotic division, as well as by disturbing antioxidant system balance [30,31]. For example, in mustard (Brassica juncea), microplastic exposure reduced germination rate from 78% (control) to 17% [32]. Conversely, some studies have reported a potential “stimulatory effect” at low MNP concentration, characterized by enhanced stress tolerance, increased root length, or elevated physiological activity [33]. However, the underlying mechanisms of such dose-dependent or biphasic effects remain poorly understood.
To date, research on the phytotoxicity of MNPs has primarily focused on cereal crops such as rice, wheat, and maize [21,30], while studies on leafy vegetables—especially fast-growing species—are notably limited. Furthermore, little is known about how different cultivation conditions and varietal traits influence plant responses to MNPs exposure [33]. For instance, under hydroponic conditions, polypropylene microplastics had minimal effects on seed germination of tomato and cherry tomato, but significantly affected root growth and nutrient uptake, with responses differing between cultivars [34]. Under soil conditions, polyethylene microplastics markedly inhibited germination and root elongation in black soybean, whereas tomato showed greater tolerance, with responses varying over time [35].
Spinach (Spinacia oleracea L.) is a widely cultivated leafy vegetable of high nutritional and economic value [36], characterized by a short life cycle, rapid growth, and a highly active root system during the seedling stage, making it a suitable model for investigating plant responses to environmental stressors [37,38]. Therefore, this study selected two spinach cultivars with differing seasonal adaptability and employed both hydroponic and soil culture systems to systematically assess the effects of PVC-MNPs on seed germination, sprout growth, and antioxidant responses. Principal component analysis (PCA) was further applied to identify the key physiological variables and their relative contributions under different treatments. These findings aim to provide a theoretical foundation for ensuring the cultivation safety of leafy vegetables such as spinach in MNPs-contaminated environments, and to contribute to the broader understanding of MNPs-induced ecological risks in agricultural systems.

2. Materials and Methods

2.1. Experimental Materials

Two spinach (Spinacia oleracea L.) cultivars were selected as experimental materials in this study: cv. xinbofeit, classified as a winter spinach variety, and cv. connaught, categorized as an autumn spinach variety. The experiment was conducted from January to May 2025 in a plant factory with artificial lighting at the Key Laboratory of Modern Agricultural Equipment and Technology (Ministry of Education), Jiangsu University. The experimental site is located at 31°37′ N and 118°58′ E, with an altitude of 5–10 m. Uniform and plump seeds were selected, and surface sterilization was performed by soaking the seeds in 0.1% potassium permanganate (KMnO4) solution for 10 min. The seeds were then thoroughly rinsed multiple times with distilled water to remove any residual KMnO4 solution, and subsequently kept ready for sowing.

2.2. Experimental Design

Polyvinyl chloride micro-nanoplastics (PVC-MNPs) were used in this experiment and were supplied by Shenzhen Guangyuan Plastics Co., Ltd. (Shenzhen, China). The average particle size of the PVC-MNPs was 100 nm, with a particle size distribution ranging from 10 to 1500 nm. For solution preparation, different masses of PVC-MNPs were weighed and added to a small volume of deionized water, then stirred on a magnetic stirrer for 10 min. The pre-dispersed suspension was transferred to a volumetric flask and diluted to volume. The flask was then placed in an ultrasonic cleaner for 15 min to further disperse PVC aggregates and ensure uniform distribution. PVC-MNPs suspensions of 0, 1, 10, 50, 100, and 200 mg/L were prepared, corresponding to treatments H0, H1, H2, H3, H4, and H5, respectively (Table 1). Sterilized forceps were used to evenly place rinsed seeds of the two spinach cultivars on moistened filter paper in Petri dishes, with 25 seeds per dish. Each dish received 5 mL of the respective PVC-MNPs solution and was incubated in a dark growth chamber at 20 °C. During germination, 5 mL of the corresponding solution was added daily. Each treatment was replicated three times.
Sandy topsoil (10–20 cm) was collected from the experimental field of Jiangsu University, air-dried, and sieved through a 10-mesh screen. The sieved soil was sterilized at high temperature and thoroughly mixed with different amounts of PVC-MNPs to prepare soil mixtures with mass concentrations of 0.0%, 0.1%, 0.2%, 0.5%, 1.0%, and 2.0%, corresponding to treatments S0, S1, S2, S3, S4, and S5, respectively (Table 1). The mixtures were placed in flat-bottom culture trays (L54 cm × W28 cm × H5.5 cm). Uniformly sterilized seeds were sown in the soil with inter-row spacing greater than 5 cm. After sowing, the seeds were covered with soil and lightly sprayed with distilled water. The trays were covered with plastic film for moisture retention and incubated in a climate-controlled chamber at 20 °C. During germination, 100 mL of distilled water was evenly sprayed onto the soil daily. Each treatment was repeated three times.
Following seed germination, spinach sprouts were cultivated for an additional 10 days under fully controlled environmental conditions. Illumination was provided by LED smart light sources with a photosynthetic photon flux density (PPFD) of 200 μmol/(m2·s) and a photoperiod of 12 h/d. Other environmental conditions included a day/night temperature of (20 ± 1)/(16 ± 1) °C and relative humidity of (70 ± 5)/(60 ± 5)%.

2.3. Measurement Indices and Methods

Seed germination of the two spinach cultivars was recorded daily at a fixed time. On day 8, the final germination data for all treatments were collected. Germination rate (GR), germination potential (GP), and germination index (GI) were calculated according to the formulas described by Xu et al. [39].
GR = n/N × 100%
GP = m/N × 100%
GI = ΣGt/Dt
where n is the number of seeds germinated on day 8 (end of the experiment); N is the total number of seeds tested; m is the number of seeds germinated on day 4 (peak germination period); Dt is the number of days required for germination; Gt is the number of seeds germinated on day t corresponding to Dt.
After germination, sprouts were continuously cultivated for 10 days under the same environmental conditions. For each treatment, 10 spinach sprouts were randomly selected, and the bud length and root length of spinach sprouts were measured using a vernier caliper. Additionally, 6 sprouts per treatment were randomly selected, rinsed with distilled water, and gently blotted with absorbent paper to remove surface moisture. The sprouts were then rapidly ground under low temperature conditions. After centrifugation and extraction, superoxide dismutase (SOD) activity was determined using the nitroblue tetrazolium (NBT) method [40], and peroxidase (POD) activity was measured using the guaiacol method [41].

2.4. Data Processing and Statistical Analysis

Experimental data analysis and figure plotting were performed using Microsoft Excel 2019 and OriginPro 2024. Statistical significance analysis was conducted using IBM SPSS Statistics v27.0. One-way analysis of variance (ANOVA) was carried out, and multiple comparisons were performed using the Waller–Duncan method at a significance level of p < 0.05. Bar graphs for multiple groups and principal component analysis (PCA) were conducted and visualized in OriginPro 2024, also at a confidence level of 0.05.

3. Results

3.1. Effects of PVC-MNPs on Spinach Seed Germination

Germination rate, germination potential, and germination index are important indicators reflecting seed viability, germination speed, and uniformity. As shown in Figure 1, except for cv. connaught under soil cultivation, the germination rate of both spinach cultivars significantly increased with increasing concentrations of PVC-MNPs within a certain range (1–100 mg/L in hydroponic conditions and 0.1–1.0% in soil conditions). When the concentration of PVC-MNPs was 1 mg/L (hydroponic) or 0.1% (soil), there was no significant difference in germination rate compared to the control (H0 and S0). However, when the concentration exceeded 100 mg/L (hydroponic) or 1.0% (soil), the germination rate of both cultivars showed a declining trend.
As shown in Figure 2, under hydroponic conditions, the germination potential of cv. xinbofeit exhibited a gradual increase with rising concentrations of PVC-MNPs, whereas cv. connaught showed an initial increase followed by a decline. No significant difference in germination potential was observed between the treatment and the control for cv. xinbofeit at 0.1 mg/L and for cv. connaught at 200 mg/L. Under soil conditions, both cultivars displayed a similar trend: germination potential increased initially and then decreased with increasing PVC-MNP concentration. Specifically, germination potential was significantly lower than the control at concentrations of 0.1% and 2.0%; no significant difference was observed at 0.2%; and germination potential was significantly higher than the control at 0.5% and 1.0%.
As shown in Figure 3, under hydroponic conditions, all PVC-MNPs treatments significantly increased the germination index of spinach seeds compared to the control. For cv. xinbofeit, germination index increased progressively with rising PVC-MNP concentrations, reaching the highest values at 100 and 200 mg/L, with no significant difference between these two treatments. In contrast, cv. connaught exhibited a rise-then-decline pattern, with the highest germination index observed at 100 mg/L, which was significantly higher than all other treatments. Under soil conditions, both cultivars exhibited a similar trend, where germination index increased initially and then decreased with increasing PVC-MNP concentrations. The highest germination index for both cultivars was observed at 1.0%. At 0.1% and 2.0% PVC-MNP concentrations, germination index was significantly lower than the control. Conversely, at 0.5% and 1.0%, germination index was significantly higher than the control for both cultivars.

3.2. Effect of PVC-MNPs on the Growth of Spinach Sprouts

Bud length and root length of spinach sprouts reflect the growth potential of the embryonic shoot and the ability of the radicle to penetrate the substrate. As shown in Table 2, under hydroponic conditions, both bud length and root length of the two spinach cultivars exhibited an initial increase followed by a decline with increasing PVC-MNP concentrations. At 10 mg/L, no significant differences were observed in bud length or root length compared to the control. The maximum bud length and root length were recorded at 100 mg/L for both cultivars, although the values for cv. connaught were slightly lower than those for cv. xinbofeit. Notably, the bud length and root length of cv. xinbofeit were significantly greater than the control, whereas those of cv. connaught showed no significant difference.
Under soil conditions, both bud length and root length of spinach sprouts showed an initial increase followed by a decline with increasing PVC-MNP concentrations (Table 3), with the highest values observed at 1.0%. Due to varietal differences, the bud length and root length of cv. connaught were consistently lower than those of cv. xinbofeit. At PVC-MNP concentrations of 0.1% and 2.0%, no significant differences in bud length and root length were observed compared to the control.

3.3. Effect of PVC-MNPs on the Antioxidant Properties of Spinach Sprouts

Superoxide dismutase (SOD) and peroxidase (POD) are key antioxidant enzymes that reflect the degree of oxidative stress experienced by plants under environmental adversity. Under hydroponic conditions, SOD and POD activities in spinach sprouts of both cultivars exhibited an initial increase followed by a decline as PVC-MNP concentrations increased (Table 4). However, the concentration at which maximum enzyme activity occurred differed between cultivars. For cv. xinbofeit, the highest SOD and POD activities were observed at 100 mg/L. No significant differences were found in SOD and POD activities among treatments at 1, 10, and 200 mg/L. In contrast, cv. connaught exhibited peak SOD and POD activities at 50 and 100 mg/L, with no significant difference between these two concentrations. Additionally, there were no significant differences in SOD and POD activities at 1 mg/L and 200 mg/L compared to the control.
Under soil conditions, both SOD and POD activities in spinach sprouts of the two cultivars exhibited a trend of initially increasing and then decreasing with increasing concentrations of PVC-MNPs (Table 5). However, the peak activity levels of SOD and POD occurred at different concentrations. SOD activity reached its maximum at 0.5% and 1.0% PVC-MNPs, with no significant difference between these two treatments. POD activity peaked at 1.0% PVC-MNP concentration. At 0.1%, neither SOD nor POD activities showed significant differences compared to the control.

3.4. Principal Component Analysis of Spinach Sprout Growth

Principal component analysis (PCA) under hydroponic conditions revealed that the first principal component (PC1) and the second principal component (PC2) explained 81.4% and 11.7% of the total variance, respectively, accounting for a cumulative contribution of 93.1% (Figure 4a). Germination characteristics, growth parameters, and antioxidant enzyme activities contributed positively and substantially to PC1. Under different treatments, cv. xinbofeit exhibited higher germination characteristics and antioxidant enzyme activities in the treatments with the PVC-MNP concentration of 50,100, and 200 mg/L, with these samples located on the right side of the PC1 axis. Notably, the treatment with the PVC-MNP concentration of 200 mg/L was distinctly separated from other treatments. In contrast, most samples of cv. connaught were clustered on the left side of the PC1 axis. These results indicate that cv. xinbofeit demonstrated better overall performance under high-concentration treatments in hydroponic conditions. The loading plot showed that germination rate, SOD, and POD were the major contributing factors to PC1.
Under soil conditions, PC1 and PC2 explained 88.4% and 6.2% of the total variance, respectively, with a cumulative contribution of 94.6% (Figure 4b). Similar to the hydroponic condition, germination characteristics, morphological growth, and antioxidant enzyme activities exhibited strong positive contributions to PC1, which primarily distinguished the different treatments. Samples of cv. xinbofeit under the treatments with the PVC-MNP concentration of 0.5 and 1.0% were distributed on the right side of the PC1 axis, indicating superior germination and physiological performance. In contrast, cv. connaught samples were predominantly located on the left side of the PC1 axis under most treatments. Under high concentrations of PVC-MNPs, both cv. xinbofeit and cv. connaught samples were positioned far from other treatments. The loading plot indicated that germination potential, germination index, root length, SOD, and POD were the primary contributors to the principal components.

4. Discussion

4.1. Seed Germination Characteristics

In recent years, micro-nanoplastics (MNPs) have emerged as a novel class of environmental contaminants, attracting growing attention in the fields of plant physiological ecology and environmental science [32,42]. The widespread use of plastic films and mulches in greenhouse crop production further exacerbates the accumulation of MNPs in agricultural systems [43,44]. Previous studies have demonstrated that MNPs can interfere with seed germination and sprout development through mechanisms such as physical obstruction, oxidative stress, and disruption of endogenous hormonal signaling [21,45]. In this study, spinach, known for its relatively strong stress tolerance, was selected as the model crop to systematically assess the effects of different concentrations of polyvinyl chloride micro-nanoplastics (PVC-MNPs) on germination characteristics, morphological development, and antioxidant enzyme activity under two cultivation systems: hydroponics and soil culture. Two spinach cultivars, cv. xinbofeit and cv. connaught, were included in the experiment.
Seed germination rate, germination potential, and germination index are key indicators reflecting seed viability, germination speed, and uniformity, and are known to be highly sensitive to environmental stressors [46,47]. The results of this study revealed that under low to moderate PVC-MNP concentrations (1–100 mg/L in hydroponics and 0.1–1.0% in soil conditions), germination indices of both cultivars were significantly enhanced compared to the control groups (H0 or S0), with cv. xinbofeit exhibiting particularly pronounced improvements. This enhancement may be attributed to a stimulatory effect of low concentrations of PVC-MNPs on seed coat permeability or enzyme activity, facilitating water uptake and activation of endogenous hormones, thereby promoting germination [22,48,49]. These findings align with the results reported by Guo et al., who observed a germination-promoting effect of low concentrations of polystyrene MNPs on spinach seeds [50]. However, the results contrast with those of Bosker et al., who reported significant inhibition at concentrations as low as 100 mg/L [21]. The discrepancy may be due to differences in particle size, as the <5 nm MNPs used in Bosker’s study may have exhibited stronger adsorption to seed surfaces, consequently impeding germination [45].
In contrast, when PVC-MNP concentrations were elevated to 200 mg/L or 2.0%, germination rates of both cultivars declined, suggesting that higher concentrations of MNPs may inhibit germination by forming a physical barrier on the seed surface, thereby restricting water and gas exchange, or by inducing intracellular oxidative stress [51]. Similar inhibitory effects have been reported in several other plant species, including Arabidopsis thaliana [46], Whitetip clover [47], rice [31], and lettuce [52], although sensitivity to MNPs exposure varies across plant species and cultivars [52].
Notably, under hydroponic conditions, cv. xinbofeit demonstrated greater resilience to high PVC-MNP concentration compared to cv. connaught. This suggests that winter-adapted cultivars may possess stronger resistance to MNPs-induced stress than autumn cultivars, potentially due to enhanced expression of stress-responsive genes linked to cold tolerance [53,54]. However, to date, no authoritative studies have directly compared the differential responses of winter versus autumn cultivars to MNPs exposure.

4.2. Morphological Characteristics of Sprout Growth

Bud length and root length are key indicators of embryonic shoot development and radicle emergence, reflecting the potential for subsequent vegetative growth in spinach [34,55]. Previous studies have reported that low concentrations of nanoplastics can promote root elongation in crops such as wheat, while higher concentrations or larger-sized microplastics tend to inhibit both root and shoot growth [22]. In the present study, exposure to low and moderate concentrations of PVC-MNPs—ranging from 1 to 100 mg/L under hydroponic conditions and 0.1–1.0% under soil conditions—led to varying degrees of enhancement in both bud and root length across the two spinach cultivars. The most pronounced growth was observed at 100 mg/L (hydroponics) and 1.0% (soil), suggesting that moderate levels of PVC-MNPs may have a stimulatory effect. These findings are in line with those reported by Guo et al. [56] and Xu et al. [57].
In contrast, sprout growth—particularly root elongation—was significantly inhibited under higher PVC-MNP concentration. This result is consistent with findings by Silva et al. [58] and may be attributed to the toxic effects of micro-nanoplastics on the meristematic tissue at root tips and their interference with cell wall structure [53]. Additionally, the inhibition may involve disruption of critical metabolic pathways such as amino acid biosynthesis and the phenylpropanoid pathway, ultimately impairing nutrient uptake and energy metabolism [23,59].
Marked differences were also observed between the two cultivars: cv. xinbofeit consistently exhibited superior bud and root growth under all treatments, indicating higher physiological adaptability and genetic stability in response to plastic-induced stress [57]. Moreover, the effects of MNPs exposure varied between hydroponic and soil-cultured systems. This may be due to differences in plastic particle bioavailability and root uptake mechanisms under distinct cultivation modes; in hydroponic systems, particles are more likely to be in direct contact with the root surface, thus exerting stronger effects [23].
In summary, the growth responses of spinach sprouts to PVC-MNPs followed a concentration-dependent trend characterized by stimulation at low doses and inhibition at higher levels. This “low-dose promotion, high-dose inhibition” pattern likely results from oxidative stress induction, metabolic disruption, and alterations in the rhizosphere environment.

4.3. Antioxidant Capacity of Sprouts

SOD and POD are key enzymatic components of the plant antioxidant defense system. Their activity levels reflect the extent of a plant’s physiological response to external environmental stress [12]. In this study, the activities of both enzymes were significantly upregulated under moderate concentrations of PVC-MNPs. This observation is consistent with findings by Guo et al. [47] and Li et al. [60], suggesting that spinach sprouts enhance their enzymatic antioxidant capacity at this stage to scavenge excess reactive oxygen species (ROS) and maintain cellular metabolic homeostasis [23,56]. Specifically, cv. xinbofeit exhibited the highest SOD and POD activities at 100 mg/L (hydroponics) and 1.0% (soil), indicating a robust oxidative stress response. In contrast, cv. connaught reached its peak enzyme activity at 50–100 mg/L, implying a higher sensitivity and narrower stress tolerance range. This may be attributed to differences in innate genetic resistance and cultivar-specific growth cycles [23,53].
Notably, under high concentrations (200 mg/L and 2.0%), SOD and POD activities declined in both cultivars, suggesting that the antioxidant defense system may have been overwhelmed and lost its protective efficiency [61]. This trend aligns with findings from Ren et al. [46] in Arabidopsis thaliana, where excessive oxidative stress led to enzyme system fatigue. In summary, PVC-MNPs induce oxidative stress in spinach sprouts, triggering a concentration-dependent response: moderate doses activate antioxidant defenses, while higher concentrations suppress enzymatic activity. This “low-dose stimulation, high-dose inhibition” effect underscores the dual role of MNPs in modulating oxidative metabolism.

4.4. Principal Component Analysis

The results of PCA in this study further elucidated the correlations among measured variables under different treatments and their contributions to cultivar-specific responses. To date, PCA-based assessments of MNPs’ impacts on spinach or similar crops remain relatively scarce. Under hydroponic conditions, the first two principal components (PC1 and PC2) together accounted for 93.1% of the total variance. Variables such as germination rate, germination index, SOD activity, POD activity, and bud length showed the highest loadings on PC1, indicating their dominant role in differentiating treatment effects. These findings are consistent with those of Yu et al. [55]. Cultivar xinbofeit was predominantly distributed on the right side of the PC1 axis across the 50–200 mg/L PVC-MNPs treatment, reflecting superior overall physiological performance. Notably, under the 200 mg/L treatment, this cultivar exhibited a pronounced deviation, suggesting enhanced adaptability to high PVC-MNP concentration. In contrast, cv. connaught was mainly clustered on the left side of PC1, indicative of weaker physiological responsiveness.
A similar pattern was observed under soil cultivation. Cultivar xinbofeit showed favorable physiological traits, particularly at PVC-MNP concentration of 0.5–1.0%, whereas most samples of cv. connaught were distributed along the negative axis range, further supporting the existence of genotype-dependent responses to PVC-MNPs stress. These results are in line with trends observed in other experimental indicators. Loading plots revealed that germination rate, germination index, germination potential, root length, and antioxidant enzyme activities (SOD and POD) were the key variables contributing to group differentiation. These indicators serve as critical reference points in the phytotoxicological evaluation of microplastics.

5. Conclusions

This study systematically evaluated the effects of varying concentrations of PVC-MNPs on seed germination and early sprout growth of two spinach cultivars under both hydroponic and soil conditions. The results revealed a typical dose-dependent response. Moderate to low concentrations of PVC-MNPs promoted germination rate, bud elongation, and antioxidant enzyme activities—particularly in cv. xinbofeit—whereas high concentrations significantly inhibited seed germination and root development, suppressed SOD and POD activities, and induced oxidative stress. The results of PCA further highlighted the physiological divergence between cultivars and identified key variables contributing to treatment differentiation. Overall, these findings suggest that PVC-MNPs may exert a regulatory effect on early plant development within a limited concentration range; however, their potential ecological risks should not be overlooked. This study provides a theoretical foundation for understanding the physiological and ecological impacts of MNPs on crop species and contributes to the risk assessment of micro-nanoplastics in agricultural ecosystems.

Author Contributions

Conceptualization, Z.Z. and W.G.; methodology, Z.Z. and W.G.; validation, J.S., R.Z. and X.B.; formal analysis, J.S., R.Z. and X.B.; investigation, J.S., R.Z. and X.B.; data curation, J.S., R.Z. and X.B.; writing—original draft preparation, J.S., R.Z., X.B. and F.J.; writing—review and editing, Z.Z. and W.G.; visualization, J.S. and F.J.; supervision, J.S. and F.J.; funding acquisition, Z.Z. and W.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (Amount of funding, 1400 USD; Project No. PAPD-2023-87), Key Laboratory of Desert-Oasis Crop Physiology, Ecology and Cultivation, MOARA, (Amount of funding, 5000 USD; Project No. xjnkywdzc-2025002-01-03), the Jiangsu University Undergraduate Innovation Training Program (Amount of funding, 350 USD; Project No. X2025102990709) and the Jiangsu University Scientific Research Project (Amount of funding, 200 USD; Project No. 24A056).

Data Availability Statement

The data used and presented in this paper are available upon request from the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

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Horticulturae 11 01062 g001
Figure 1. Effect of PVC-MNPs on the germination rate of spinach seeds. In the treatment names, “H” represents the Hydroponic mode and “S” represents the Soil mode, while the number following the letter indicates the PVC-MNP concentration. The number of “*” indicates the degree of significant difference between the treatment and CK, and “*”, “**”, and “***” indicate the difference levels at confidence levels of 0.05, 0.01, and 0.001, respectively.
Figure 1. Effect of PVC-MNPs on the germination rate of spinach seeds. In the treatment names, “H” represents the Hydroponic mode and “S” represents the Soil mode, while the number following the letter indicates the PVC-MNP concentration. The number of “*” indicates the degree of significant difference between the treatment and CK, and “*”, “**”, and “***” indicate the difference levels at confidence levels of 0.05, 0.01, and 0.001, respectively.
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Horticulturae 11 01062 g002
Figure 2. Effect of PVC-MNPs on the germination potential of spinach seeds. The number of “*” indicates the degree of significant difference between the treatment and CK, and “*” and “***” indicate the difference levels at confidence levels of 0.05 and 0.001, respectively.
Figure 2. Effect of PVC-MNPs on the germination potential of spinach seeds. The number of “*” indicates the degree of significant difference between the treatment and CK, and “*” and “***” indicate the difference levels at confidence levels of 0.05 and 0.001, respectively.
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Horticulturae 11 01062 g003
Figure 3. Effect of PVC-MNPs on the germination index of spinach seeds. The number of “*” indicates the degree of significant difference between the treatment and CK, and “*”, “**”, and “***” indicate the difference levels at confidence levels of 0.05, 0.01, and 0.001, respectively.
Figure 3. Effect of PVC-MNPs on the germination index of spinach seeds. The number of “*” indicates the degree of significant difference between the treatment and CK, and “*”, “**”, and “***” indicate the difference levels at confidence levels of 0.05, 0.01, and 0.001, respectively.
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Horticulturae 11 01062 g004
Figure 4. Principal component analysis of spinach sprout germination under hydroponic (a) and soil (b) conditions. The PC1 and PC2 axes represent the primary directions of variation. Colored data points correspond to different experimental treatments, while arrows indicate the loading vectors of variables associated with the principal components.
Figure 4. Principal component analysis of spinach sprout germination under hydroponic (a) and soil (b) conditions. The PC1 and PC2 axes represent the primary directions of variation. Colored data points correspond to different experimental treatments, while arrows indicate the loading vectors of variables associated with the principal components.
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Table 1. Experimental treatments of PVC-MNPs under two different cultivation modes.
Table 1. Experimental treatments of PVC-MNPs under two different cultivation modes.
TreatmentCultivation ModePVC-MNP Concentration
cv. xinbofeitcv. connaught
H0Hydroponic0 mg·L−1
H11 mg·L−1
H210 mg·L−1
H350 mg·L−1
H4100 mg·L−1
H5200 mg·L−1
S0Soil0.00%
S10.10%
S20.20%
S30.50%
S41.00%
S52.00%
Note: In the treatment names, “H” represents the Hydroponic mode and “S” represents the Soil mode, while the number following the letter indicates the PVC-MNP concentration.
Table 2. Effect of PVC-MNPs on the growth of spinach sprouts under hydroponic conditions.
Table 2. Effect of PVC-MNPs on the growth of spinach sprouts under hydroponic conditions.
TreatmentBud Length (mm)Root Length (mm)
cv. xinbofeitcv. connaughtcv. xinbofeitcv. connaught
H012.36 ± 2.04 d9.65 ± 1.93 d13.52 ± 1.12 d10.54 ± 1.24 c
H113.96 ± 1.88 cd11.35 ± 2.38 cd13.12 ± 1.07 d11.42 ± 1.12 bc
H214.85 ± 2.03 c13.42 ± 2.36 c15.62 ± 1.56 c12.57 ± 1.40 b
H318.42 ± 1.21 ab15.74 ± 1.62 b18.22 ± 1.82 b16.81 ± 1.93 a
H420.36 ± 1.92 a18.22 ± 2.40 a20.35 ± 1.27 a17.42 ± 1.77 a
H517.73 ± 1.77 b12.05 ± 2.50 cd14.95 ± 1.37 c10.87 ± 1.29 c
Note: The results are expressed by mean ± standard deviation (SD, n = 8), and treatments with different letters are significantly different at p ≤ 0.05.
Table 3. Effect of PVC-MNPs on the growth of spinach sprouts under soil conditions.
Table 3. Effect of PVC-MNPs on the growth of spinach sprouts under soil conditions.
TreatmentBud Length (mm)Root Length (mm)
cv. xinbofeitcv. connaughtcv. xinbofeitcv. connaught
S010.63 ± 2.96 c7.63 ± 2.09 d8.87 ± 1.75 d6.52 ± 1.09 d
S110.96 ± 1.96 c7.41 ± 2.03 d7.63 ± 1.33 d6.49 ± 1.57 d
S212.74 ± 2.94 c9.62 ± 2.26 c10.7 ± 1.45 c8.74 ± 1.38 c
S315.85 ± 2.39 b14.25 ± 1.68 b13.48 ± 1.86 b11.03 ± 1.30 b
S419.63 ± 1.85 a16.74 ± 1.85 a17.52 ± 1.50 a13.72 ± 1.61 a
S511.32 ± 2.23 c7.85 ± 2.48 d9.06 ± 1.53 d7.06 ± 1.41 d
Note: The results are expressed by mean ± standard deviation (SD, n = 8), and treatments with different letters are significantly different at p ≤ 0.05.
Table 4. Effects of PVC-MNPs on the antioxidant properties of spinach sprouts under hydroponic conditions.
Table 4. Effects of PVC-MNPs on the antioxidant properties of spinach sprouts under hydroponic conditions.
TreatmentSOD (U/g)POD (U/g)
cv. xinbofeitcv. connaughtcv. xinbofeitcv. connaught
H0576.32 ± 28.52 c549.24 ± 12.63 c74.63 ± 8.78 c71.51 ± 8.98 c
H1589.41 ± 34.62 bc567.65 ± 25.62 bc78.41 ± 12.28 c84.63 ± 17.56 bc
H2588.14 ± 24.32 bc576.74 ± 22.48 b86.92 ± 15.01 bc90.42 ± 12.47 b
H3602.85 ± 25.47 b599.32 ± 32.41 ab104.60 ± 17.37 b111.98 ± 14.25 a
H4657.92 ± 32.63 a615.47 ± 19.57 a132.54 ± 11.06 a119.44 ± 17.03 a
H5564.57 ± 26.95 c552.14 ± 24.74 c75.96 ± 12.76 c69.51 ± 17.69 c
Note: The results are expressed by mean ± standard deviation (SD, n = 8), and treatments with different letters are significantly different at p ≤ 0.05.
Table 5. Effects of PVC-MNPs on the antioxidant properties of spinach sprouts under soil conditions.
Table 5. Effects of PVC-MNPs on the antioxidant properties of spinach sprouts under soil conditions.
TreatmentSOD (U/g)POD (U/g)
cv. xinbofeitcv. connaughtcv. xinbofeitcv. connaught
S0555.62 ± 12.63 c537.63 ± 19.47 d69.32 ± 12.74 d66.34 ± 14.63 d
S1554.65 ± 14.54 c557.95 ± 20.65 cd68.41 ± 9.07 d74.85 ± 13.02 cd
S2596.32 ± 24.68 b584.25 ± 15.48 b84.96 ± 11.85 bc82.41 ± 11.70 c
S3625.74 ± 22.57 a598.90 ± 26.96 ab99.74 ± 14.39 b93.52 ± 10.85 b
S4639.57 ± 18.64 a626.45 ± 28.45 a121.33 ± 10.74 a105.87 ± 12.16 a
S5572.63 ± 21.07 bc562.38 ± 19.52 c82.54 ± 12.71 c78.85 ± 12.21 cd
Note: The results are expressed by mean ± standard deviation (SD, n = 8), and treatments with different letters are significantly different at p ≤ 0.05.
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Song, J.; Zhang, R.; Bao, X.; Ji, F.; Zuo, Z.; Geng, W. Differential Responses of Spinach Cultivars to Micro-Nanoplastic Stress Under Hydroponic and Soil Cultivation Conditions. Horticulturae 2025, 11, 1062. https://doi.org/10.3390/horticulturae11091062

AMA Style

Song J, Zhang R, Bao X, Ji F, Zuo Z, Geng W. Differential Responses of Spinach Cultivars to Micro-Nanoplastic Stress Under Hydroponic and Soil Cultivation Conditions. Horticulturae. 2025; 11(9):1062. https://doi.org/10.3390/horticulturae11091062

Chicago/Turabian Style

Song, Jinxiu, Rong Zhang, Xiaotong Bao, Fang Ji, Zhiyu Zuo, and Wei Geng. 2025. "Differential Responses of Spinach Cultivars to Micro-Nanoplastic Stress Under Hydroponic and Soil Cultivation Conditions" Horticulturae 11, no. 9: 1062. https://doi.org/10.3390/horticulturae11091062

APA Style

Song, J., Zhang, R., Bao, X., Ji, F., Zuo, Z., & Geng, W. (2025). Differential Responses of Spinach Cultivars to Micro-Nanoplastic Stress Under Hydroponic and Soil Cultivation Conditions. Horticulturae, 11(9), 1062. https://doi.org/10.3390/horticulturae11091062

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