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Article

Optimizing Selenium Application for Enhanced Quality and Nutritional Value of Spring Tea (Camellia sinensis)

by
Qing Liao
1,
Pan-Xia Liang
2,
Ying Xing
1,
Zhuo-Fan Yao
3,
Jin-Ping Chen
1,
Li-Ping Pan
1,
Yao-Qiu Deng
4,
Yong-Xian Liu
1 and
Dong-Liang Huang
1,*
1
Guangxi Key Laboratory of Arable Land Conservation, Guangxi Key Laboratory of Sugarcane Genetic Improvement, Key Laboratory of Sugarcane Biotechnology and Genetic Improvement (Guangxi), Guangxi Academy of Agricultural Sciences, Nanning 530007, China
2
College of Agricultural Engineering, Guangxi Vocational University of Agriculture, Nanning 530007, China
3
Guangxi Guiping Xishan Bishui Tea Garden Co. Ltd., Guiping 537200, China
4
Guiping Cash Crops Workstation, Guiping 537200, China
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(4), 423; https://doi.org/10.3390/horticulturae11040423
Submission received: 8 March 2025 / Revised: 12 April 2025 / Accepted: 14 April 2025 / Published: 16 April 2025
(This article belongs to the Special Issue Advances in Developmental Biology and Cultivation Techniques of Tea Plants)
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Abstract

:
Tea (Camellia sinensis) is a globally cherished beverage, valued for its flavor and health benefits, largely attributed to bioactive compounds like polyphenols and amino acids. Selenium (Se), an essential trace element for humans and animals, plays a dual role in promoting plant growth and enhancing human health, yet its impact on tea quality remains underexplored. In this work, the effects of selenium application rate (with 0, 150, 225, and 300 g·ha−1 of Se) on soil selenium availability, enzyme activity, and the biochemical composition of spring tea, including chlorophyll, polyphenols, free amino acids, and polysaccharides, were studied. Results show that selenium application significantly increased soil selenium availability, with higher rates promoting its conversion into bioavailable forms. Soil enzyme activities, such as sucrase and urease, were notably influenced by selenium. In tea leaves, selenium content and glutathione peroxidase activity increased, while chlorophyll content initially rose but declined at higher application rates, with the Se225 treatment (225 g·ha−1 of Se) yielding optimal results. Selenium reduced polyphenol content, increased free amino acids, and lowered the phenol-to-amino acid ratio, improving tea sensory quality. Polysaccharide content also peaked at the Se225 treatment. These findings highlight the potential of selenium-enriched tea as a functional food and provide a scientific basis for optimizing selenium application in tea cultivation.

1. Introduction

Tea (Camellia sinensis) is one of the most widely consumed beverages globally, valued not only for its rich cultural heritage, but also for its distinctive flavor profiles and extensive health benefits [1]. As a cornerstone of daily life for millions, tea consumption has been associated with improved cardiovascular health, enhanced immune function, and a reduced risk of chronic diseases, attributed to its abundance of bioactive compounds, including polyphenols, amino acids, and vitamins [1,2]. With the increasing demand for high-quality tea, significant attention has been directed toward understanding the factors influencing its sensory and nutritional properties, including agronomic practices, environmental conditions, and the role of trace elements [3].
Among trace elements, selenium (Se) has attracted considerable attention, owing to its dual functionality as an essential nutrient for humans and a beneficial element for plants [4,5]. Selenium is a key component of selenoproteins, which are crucial for antioxidant defense, thyroid hormone metabolism, and immune function in humans [6,7]. In plants, selenium has been demonstrated to promote growth, enhance stress tolerance, and stimulate the accumulation of beneficial compounds, such as phenolics, flavonoids, and vitamins [8,9]. These properties render selenium a promising candidate for biofortification strategies designed to enhance the nutritional quality of crops, including tea [10,11].
Studies have demonstrated that selenium application can significantly enhance tea quality [12,13,14]. Additionally, selenium-enriched tea has demonstrated potential in mitigating stress-related diseases [15]. Despite these promising findings, the effects of selenium on tea quality remain insufficiently understood. Furthermore, the application of selenium in tea cultivation presents significant challenges. Excessive selenium can lead to toxicity, adversely affecting plant growth and compromising tea quality [16]. Therefore, determining the optimal dosage, application methods, and timing for selenium supplementation is essential for maximizing its benefits while mitigating potential risks [17].
Given the growing interest in selenium-enriched tea as a functional food, there is a pressing need for comprehensive research to address the existing knowledge gaps. This study aims to explore the effects of selenium on tea quality, with a specific focus on its influence on key biochemical components, such as chlorophyll, polyphenols, free amino acids, and polysaccharides. This research aims to establish a scientific foundation for the development of selenium-enriched tea products. Moreover, the findings will contribute to the optimization of agronomic practices, ensuring sustainable, high-quality tea production amid rising demand.

2. Materials and Methods

2.1. Experimental Site and Materials

The study was conducted at the Xishan Bishui Tea Plantation Base, located in Mengxu Town, Guiping City, Guangxi Province (109°56′59″ E, 23°18′36″ N, altitude 46 m). The soil type was classified as lateritic red soil based on Chinese Soil Taxonomic Classification (2001) [18] and the physicochemical properties are shown in Table 1. The tea variety used in the experiment was Jinxuan, with trees aged 15 years. The selenium fertilizer used was an organic Se-rich fertilizer supplied by Suzhou Xigu Technology Co., Ltd. (Suzhou, China), with a selenium concentration of 1000 mg·kg−1.

2.2. Experimental Design and Sampling

Four treatments were established, with Se concentration of 0, 150, 225, and 300 g·ha−1 (0, 150, 225, and 300 kg·ha−1 of Se-rich fertilizer), designated as CK, Se150, Se225, and Se300, respectively, based on previous work [19,20]. The selenium fertilizer was applied by evenly distributing it around the root zone of the tea plants and subsequently covering it with a thin soil layer. Selenium application was conducted on 26 February 2024. Each plot was 7 m long, with 1.7 m row spacing, containing three rows of tea plants. Each treatment was replicated three times to ensure statistical reliability. Other field management practices adhered to standard spring tea cultivation practices. On 19 April 2024, spring tea and soil samples were collected for analysis. The top two leaves and a bud were collected from the spring tea, rinsed thrice with distilled water, blotted dry using filter paper, and the fresh leaves were utilized for the analysis of antioxidant enzymes and chlorophyll content. The remaining leaves were heated at 105 °C for 5 min to deactivate enzymes, dried at 55 °C, ground into a fine powder, and sieved for subsequent analyses. Soil samples were collected from the root zone of the tea plants, air-dried, crushed, and sieved through 30-, 60-, and 100-mesh screens to determine soil enzyme activity, available selenium content, and selenium speciation, respectively.

2.3. Measurement of Plant Samples

Reagents: All the chemical reagents were domestically produced and of analytical grade.
Glutathione peroxidase (GSH-Px) activity was measured using the DTNB (5,5′-Dithiobis-(2-nitrobenzoic acid)) method [21]. Fresh leaves (0.5 g) were homogenized in 3 mL of sodium phosphate buffer (0.2 mol·L−1, pH 6.2) containing 1 mM EDTA-2Na and 5% PVP, kept in an ice bath. The homogenate was centrifuged at 3000 rpm for 10 min, and the supernatant was further centrifuged at 12,000 rpm for 5 min. The final supernatant was used to assay GSH-Px activity.
Chlorophyll content was quantified following the standard “Determination of chlorophyll content in fruits, vegetables and derived products—Spectrophotometry method (NY/T 3082-2017)”. Leaf samples were homogenized, and 0.5 g was extracted with 10 mL of ethanol–acetone (1:1, v/v) for 5 h in darkness. Absorbance of the filtered extract was measured at 645 nm and 663 nm.
Polyphenol content was quantified following the standard “Determination of total polyphenols and catechins content in tea (GB/T 8313-2018)” method. Tea leaf powder (0.2 g) was extracted twice with 5 mL of 70% (v/v) methanol at 70 °C, centrifuged, and diluted to 10 mL. The extracts were filtered through a 0.45 µm organic membrane filter prior to analysis. A series of gallic acid standard solutions were prepared at concentrations of 10, 20, 30, 40, and 50 µg·mL−1 for calibration. Aliquots of the filtered extracts were mixed with Folin–Ciocalteu reagent and Na2CO3 solution, and the absorbance was measured at 765 nm.
Polysaccharides were analyzed according to the standard “Determination of crude polysaccharides in edible mushroom—Spectrophotometric method (NY/T 1676-2008)”. the procedure was as follows: Exactly 0.5 g of tea powder was weighed using an analytical balance (0.1 mg precision) and transferred into a 50 mL screw-cap centrifuge tube. The sample was moistened with 5 mL distilled water, followed by a gradual addition of 20 mL anhydrous ethanol. The mixture was vortex-mixed thoroughly and subsequently subjected to ultrasonic extraction for 30 min. The mixture was centrifuged at 4000× g for 10 min, and the supernatant was discarded. The precipitate was washed with 10 mL of 80% (v/v) ethanol solution, followed by repeat centrifugation. The precipitate was transferred to a round-bottom flask containing distilled water. After adding 50 mL of distilled water, the flask was fitted with an air condenser and extracted in a boiling water bath (Jiangsu Jinyi Instrument Technology Co., Ltd., Jintan, China) for 2 h. After cooling to room temperature, the solution was filtered, and the supernatant was transferred to a 100 mL volumetric flask. The residue was washed 2–3 times, with washings combined in the flask and diluted to volume with water to obtain the test solution. A 1.0 mL aliquot of the test solution was pipetted, mixed with 1 mL of 5% phenol solution, and vortexed thoroughly. Five milliliters of concentrated sulfuric acid was added rapidly, and the mixture was allowed to stand for 10 min. After thorough vortex mixing, the solution was incubated in a 30 °C water bath for 20 min. Absorbance was measured at 490 nm.
Plant selenium content was determined following the standard “National food safety standard–Determination of selenium in food (GB 5009.93-2017)”. Tea leaf powder (0.5 g) was digested overnight in HNO3-HClO4 (9:1) at room temperature. The mixture was heated on a hotplate (with HNO3 replenishment) until a clear solution was obtained (~2 mL remaining). Then, 6 mol·L−1 HCl was added, and the solution was reheated until clear white fumes appeared. After cooling, the digestate was transferred to a 10 mL flask. Then, 2.5 mL of 100 g·L−1 K3[Fe(CN)6] solution was added, and the mixture was diluted to volume with deionized water. Selenium content was quantified by hydride generation-atomic fluorescence spectrometry (HG-AFS), with 5% HCl as carrier solution and 8 g·L−1 NaBH4 in 0.5% NaOH as reductant.

2.4. Measurement of Soil Samples

The activities of soil catalase, soil urease, soil sucrase, and soil acid phosphatase were measured using enzyme activity assay kits obtained from Solarbio Company (Shanghai, China), in units per gram dry soil per 24 h: catalase (mmol), urease (μg), sucrase (mg), and acid phosphatase (nmol).
The soil-available selenium content was quantified following the standardized protocol outlined in “Determination of available selenium in soil—Hydride generation atomic fluorescence spectrometry (NY/T 3420-2019)”. Exactly 1.0 g of soil was weighed into a 15 mL centrifuge tube (Nantong Haimen District Moled Experimental Equipment Factory, Nantong, China) using a 0.1 mg precision balance (Want Balance Instrument Co., Ltd., Changzhou, China). To this, 10 mL of 0.10 mol·L−1 KH2PO4 solution (pH 6.0) was added. The mixture was shaken at 1500 rpm and 30 °C for 80 min, followed by centrifugation at 3000 rpm for 15 min. A 5 mL aliquot of the supernatant was transferred to a microwave digestion vessel. Then, 7 mL concentrated HNO3 and 1 mL H2O2 were added, and microwave digestion was performed. The digestate was evaporated to near-dryness on a 160 °C hotplate and subsequently cooled. Then, 5 mL of 6 mol·L−1 HCl was added, and the solution was heated until a clear solution with white HClO4 fumes appeared. After cooling, the solution was transferred to a 10 mL volumetric flask, mixed with 1 mL of 100 g·L−1 K3[Fe(CN)6], and diluted with 5% HCl. Selenium quantification was performed using atomic fluorescence spectrometry (AFS), with NaBH4 as the reductant and 5% HCl as the carrier solution.
Soil selenium forms were determined using the sequential extraction method [22], which categorizes soil selenium into five distinct binding forms, including soluble Se (SOL-Se), exchangeable Se and carbonate-bound Se (EX-Se), iron (Fe)/manganese (Mn) oxide-bound Se (FMO-Se), organic matter-bound Se and elemental Se (OM-Se), and residual Se (RES-Se) [23]. Air-dried soil samples, sieved through a 100-mesh screen, were precisely weighed and transferred into sterile polyethylene centrifuge tubes. Sequential extraction was carried out at a soil-to-solution ratio of 1:10, with extraction solutions added incrementally to ensure continuous extraction.

2.5. Data Analysis

Statistical analyses were performed using Microsoft Excel 2017 and SPSS 19.0. A one-way ANOVA followed by Duncan’s multiple range test was applied for comparisons. Triplicate experiments were conducted, with results expressed as mean ± standard error. Significance thresholds were defined as p < 0.05 (significant) and p < 0.01 (highly significant).

3. Results

3.1. Selenium Application Enhances the Available Selenium in Soil

The available selenium content in soil was significantly higher in all selenium-treated groups than in the CK group (p < 0.01). Furthermore, significant differences in available selenium content were observed among the selenium treatments. Soil-available selenium content showed a positive correlation with selenium application rates, with the Se300 treatment showing the highest content (Figure 1).
Further analysis of selenium forms in the soil (Table 2) demonstrated that the concentrations of SOL-Se and EX-Se were significantly elevated in the selenium-treated groups compared to the CK group, with increases of 0.90–1.43% and 6.75–8.22%, respectively.

3.2. Selenium Application Exerts Diverse Effects on Soil Enzyme Activity

The impact of varying selenium application rates on soil enzyme activities showed significant variation (Table 3). Selenium application enhanced soil sucrase activity; however, higher application rates resulted in a gradual decline in sucrase activity. Among the selenium treatments, the Se100 treatment showed the highest soil sucrase activity, followed by the Se225 treatment. Both treatments demonstrated significantly higher soil sucrase activity compared to the CK and Se300 treatments. Although the Se300 treatment exhibited an increase in soil sucrase activity relative to the CK treatment, the difference was not statistically significant.
Regarding soil urease activity, selenium application showed an inhibitory effect, with soil urease activity progressively declining as selenium application increased. Compared to the CK treatment, the Se100 treatment exhibited no significant difference in soil urease activity, while the Se225 and Se300 treatments resulted in a significant decrease in soil urease activity, with the Se300 treatment displaying the lowest activity.
For soil acid phosphatase and catalase activities, the effects of selenium application were not statistically significant. With increasing selenium application, soil acid phosphatase activity showed a slight decline, whereas soil catalase activity initially increased before decreasing. However, no significant differences were observed in these two enzyme activities across the different selenium treatments.

3.3. Selenium Application Increases the Selenium Content in Spring Tea

The selenium content in spring tea exhibited a positive correlation with increasing selenium application rates (Figure 2). Selenium content in the Se100, Se225, and Se300 treatments was 5.27-fold, 6.69-fold, and 9.89-fold higher, respectively, than that in the CK treatment. The selenium content in selenium-treated tea leaves was significantly higher than that in the CK treatment (p < 0.01; the same applies hereafter), with significant differences among selenium treatments. The Se300 treatment yielded the highest selenium content in tea leaves.
The selenium content in the CK treatment was 0.174 mg·kg−1, whereas the selenium content in the selenium-treated tea leaves ranged from 0.919 mg·kg−1 to 1.724 mg·kg−1. Our results demonstrate that control tea leaves contained insufficient selenium to meet the standards for selenium-enriched agricultural product (GH/T 1135-2017; the required range: 0.25–4.00 mg·kg−1 for tea). However, selenium application at 100–300 kg·ha−1 effectively increased leaf selenium content to this optimal range without exceeding the safety threshold. These findings confirm that controlled selenium fertilization provides a safe and effective means of producing selenium-enriched spring tea while maintaining product quality standards.

3.4. Selenium Application Enhances GSH-Px Activity in Spring Tea

The GSH-Px activity in spring tea exhibited a positive correlation with increasing selenium application rates (Figure 3). The GSH-Px activity in the Se100, Se225, and Se300 treatments was 3.42-fold, 5.14-fold, and 5.54-fold higher, respectively, than that in the CK treatment. The GSH-Px activity in all selenium-treated tea leaves was significantly higher than that in the CK treatment (p < 0.01), with the Se300 treatment exhibiting the highest GSH-Px activity. Among the selenium treatments, no significant difference in GSH-Px activity was observed between the Se225 and Se300 treatments; however, both were significantly higher than the Se100 treatment. These findings suggest that selenium application at rates of 100–225 kg·ha−1 enhances GSH-Px activity in spring tea, thereby improving its antioxidant capacity and effectively mitigating oxidative damage to cells.

3.5. Selenium Application Increases Chlorophyll Content in Spring Tea

Various selenium treatments effectively enhanced the chlorophyll content of spring tea (Table 4). As selenium application rates increased, the contents of chlorophyll a, chlorophyll b, and total chlorophyll initially rose and subsequently declined. Compared to the CK treatment, the chlorophyll a content in the Se100, Se225, and Se300 treatments showed significant increases of 5.56%, 9.02%, and 3.51%, respectively. The chlorophyll b content exhibited significant increases of 11.56%, 28.22%, and 4.38%, respectively, whereas the total chlorophyll content showed significant increases of 7.27%, 14.51%, and 3.76%, respectively.
Among the selenium treatments, the Se225 treatment demonstrated the most pronounced increase in chlorophyll content. Furthermore, the chlorophyll a to chlorophyll b ratio in the Se225 treatment was significantly lower than that in the CK treatment, suggesting that the Se225 treatment enhanced the ability of spring tea to absorb and utilize diffuse light, thereby facilitating chlorophyll synthesis.

3.6. Selenium Application Reduces Polyphenol Content, Increases Free Amino Acid Content, and Lowers Phenol-to-Amino Acid Ratio in Spring Tea

The tea polyphenol content in the Se100, Se225, and Se300 treatments decreased by 31.41%, 25.28%, and 28.02%, respectively, relative to the CK treatment. Varying selenium application rates significantly reduced the tea polyphenol content in spring tea, with the Se100 treatment exhibiting the greatest reduction (Figure 4A).
The free amino acid content in the Se100, Se225, and Se300 treatments increased by 0.61%, 1.97%, and 3.54%, respectively, relative to the CK treatment. The free amino acid content exhibited an upward trend with increasing selenium application rates, with the Se300 treatment yielding the highest free amino acid content (Figure 4B).
The phenol-to-amino acid ratio in the Se100, Se225, and Se300 treatments decreased by 31.82%, 26.71%, and 30.49%, respectively, relative to the CK treatment. Varying selenium application rates significantly lowered the phenol-to-amino acid ratio in spring tea (Figure 4C).
In summary, selenium application decreased the tea polyphenol content, enhanced the free amino acid content, and reduced the phenol-to-amino acid ratio, thereby mitigating the astringency of the tea and improving the sensory quality of spring tea.

3.7. Selenium Application Improves Polysaccharide Content in Spring Tea

Various selenium treatments effectively enhanced the polysaccharide content in spring tea (Figure 5). As selenium application rates increased, the polysaccharide content initially increased and subsequently decreased. Compared to the CK treatment, the Se100 treatment exhibited an increase in polysaccharide content; however, the difference was not statistically significant. In contrast, the Se225 treatment demonstrated a highly significant increase in polysaccharide content, achieving the highest value. Although the Se300 treatment displayed a slight decrease compared to Se225, it still showed a significant increase relative to the CK treatment. No significant difference in polysaccharide content was observed between the Se100 and Se300 treatments. Therefore, the Se225 treatment yielded the most favorable outcome.

4. Discussion

Currently, the Chinese Nutrition Society recommends a daily selenium intake of 60–400 µg for adults [24]; however, in two-thirds of China, selenium intake remains below the minimum recommended level, resulting in “hidden hunger” due to selenium deficiency. To address hidden hunger at its root, plant-based organic selenium sources can be utilized, enabling selenium intake through the food chain and preventing diseases associated with selenium deficiency. This approach is safe, cost-effective, and practical. Enhancing the selenium content in crops through the application of exogenous selenium fertilizer represents a viable method. Exogenous selenium application includes soil fertilization and foliar spraying [25]. Foliar spraying is efficient, requires less selenium, and allows flexible control. However, it is labor-intensive, weather-dependent, and can lead to uneven distribution [26]. Soil application is more stable, easier to manage, and provides long-term benefits [27]. This study focuses on the effects of soil-applied selenium on tea plants.
Selenium application has been demonstrated to enhance the available selenium content in soil [28,29,30,31]. In this study, the available selenium content in the soil exhibited a positive correlation with increasing selenium application rates, with the highest content observed in the treatment receiving 300 kg·ha−1 of selenium. Selenium application also altered the original equilibrium of selenium forms in the soil, facilitating the conversion of highly fixed selenium forms, such as RES-Se and FMO-Se, into more bioavailable forms, such as SOL-Se and EX-Se. Thus, selenium application not only increased the available selenium content in the soil, but also optimized the composition of selenium forms, thereby enhancing the selenium enrichment capacity of spring tea.
Several studies have investigated the impact of exogenous selenium absorption on the selenium content of tea leaves [32,33]. Selenium fertilizer (4.68–28.08 g·ha−1) was applied to the soil-root system of tea plants over a 10-day period. The selenium content in the tea leaves ranged from 0.075 to 0.174 mg·kg−1, representing 0.94–2.18 times the content in the control group without selenium application [32]. However, these levels did not meet the industry standard for selenium-rich tea (0.25–4.00 mg·kg−1) as specified in the standard “Selenium-enriched agricultural products (GH/T 1135-2017)”. In a separate study, Wang et al. [33] reported that root application of exogenous selenium fertilizer at 75–375 kg·ha−1 significantly enhanced the selenium content in both spring and summer tea. In this study, conducted in a selenium-rich tea garden with a soil selenium content of 0.82 mg·kg−1, the selenium content in spring tea from the control treatment was 0.174 mg·kg−1. In contrast, root application of selenium fertilizer at 150–300 kg·ha−1 significantly elevated the selenium content in spring tea to 0.919–1.724 mg·kg−1, meeting the standards for selenium-rich tea. These findings indicate that a selenium-rich tea garden does not inherently ensure consistent production of naturally selenium-enriched tea. Appropriate selenium application in tea plants is advantageous for enhancing the selenium content in tea leaves and ensuring the safe production of selenium-enriched tea.
Research suggests that selenium-enriched tea could help prevent or manage stress-related diseases [15]. The quality of tea is influenced by various biochemical components. Glutathione peroxidase (GSH-Px) is a widely studied enzyme with an active center containing selenocysteine [34]. GSH-Px, in conjunction with other antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX), constitutes an effective defense system against lipid peroxidation. This system plays a vital role in neutralizing oxygen free radicals, which is critically important for both plants and animals [35]. An appropriate dose of selenium can significantly reduce H2O2 levels, likely due to its ability to reactivate antioxidants, particularly GSH-Px [13], as the utilization and absorption of selenium in plants are directly associated with GSH-Px activity in plant tissues [36]. In this study, the GSH-Px activity in tea leaves from all selenium-treated groups was significantly higher than that in the control group, consistent with previous findings [37,38,39]. However, some studies [40,41] suggest that selenium fertilizer may induce GSH-Px synthesis through alternative pathways, where exogenous selenium contributes to GSH-Px synthesis via other mechanisms.
Chlorophyll, the primary pigment in green tea, plays a crucial role in determining the color of the final product, with higher chlorophyll content in fresh tea leaves contributing to a richer green hue. Polyphenols, which are significant secondary metabolites in tea, exhibit antioxidant, antitumor, anti-radiation, and antibacterial properties. They are among the primary components responsible for the color, aroma, and taste of tea, directly impacting its sensory quality and physiological health benefits [42]. Amino acids are essential flavor compounds in tea, providing physiological benefits such as antioxidant activity, immune enhancement, and nerve relaxation [43]. They are also a critical factor influencing tea quality. The phenol-to-amino acid ratio serves as a critical indicator of the taste quality of green tea. High-quality green tea is typically characterized by high levels of free amino acids and a low phenol-to-amino acid ratio [44]. Polysaccharides are acidic glycoproteins associated with a significant number of mineral elements. They offer health benefits, including blood sugar reduction, blood lipid regulation, immune modulation, thrombosis prevention, and antioxidant effects [45]. The selenium content and quality components of tea are influenced by factors such as the type of selenium fertilizer, application concentration, timing, and tea plant variety [46]. Optimal selenium application can enhance photosynthetic pigments in tea leaves and improve tea quality [39,47,48]. In this study, all selenium treatments resulted in increased total chlorophyll content, reduced tea polyphenol content, elevated free amino acid content, and a lower phenol-to-amino acid ratio. Furthermore, polysaccharide content was also increased. Among the three selenium treatments, the application rate of 225 kg·ha−1 yielded the highest total chlorophyll and tea polysaccharide content, accompanied by a lower phenol-to-amino acid ratio. This treatment enhanced the color and flavor compounds, resulting in relatively superior overall quality in spring tea.
Soil enzymes are integral to numerous critical biochemical processes in the soil and serve as key biological indicators for assessing soil fertility and ecological environmental quality [49,50]. Understanding Se-enzyme interactions enables science-backed recommendations for Se fertilization, minimizing environmental risks while improving crop nutritional quality. In this study, selenium application within the range of 100–225 kg·ha−1 enhanced soil sucrase activity. However, when the selenium application rate reached 300 kg·ha−1, soil sucrase activity declined, consistent with previous findings [51]. In contrast, Fan et al. [52] reported an inhibitory effect of selenium on soil sucrase activity. This discrepancy may be attributed to variations in the physicochemical properties of the tested soils [53]. Several studies indicate that selenium inhibits soil urease activity [54], with a significant negative correlation observed between soil urease activity and selenium application rates [55]. This aligns with the findings of this study. So, elevated selenium concentrations may disrupt the transformation and supply of soil nitrogen, potentially adversely affecting tea plant growth. Therefore, when applying selenium, it is essential to consider its potential impacts on soil nitrogen cycling. Additionally, in this study, while each selenium treatment exhibited some inhibitory or activating effects on soil acid phosphatase and catalase activities, the effects were not statistically significant. These results are consistent with those reported by Cheng et al. [56] and Lin et al. [55]. In this study, the extent of selenium’s influence on the four soil enzymes varied, indicating differing sensitivities of soil enzymes to selenium. This variability underscores the complexity of soil enzyme responses to selenium and the need for further research to understand the underlying mechanisms.

5. Conclusions

Selenium treatments significantly enhance soil-available selenium content and sucrase activity while inhibiting urease activity, though they exert no significant impact on acid phosphatase or catalase activity. An application rate of approximately 225 kg·ha−1 optimizes tea quality parameters—including GSH-Px activity, chlorophyll content, and amino acid levels—without compromising soil functionality. However, long-term selenium application necessitates careful monitoring to mitigate potential trade-offs between soil functionality and plant benefits. While selenium improves soil selenium availability and sucrase activity, its inhibitory effect on urease underscores the need for periodic soil enzyme assessments. Future research should investigate selenium’s residual effects, microbial community responses, and broader ecological implications to refine sustainable application strategies.

Author Contributions

Conceptualization, Q.L., Y.-X.L. and D.-L.H.; methodology, Q.L., P.-X.L., Y.X., Z.-F.Y., J.-P.C., L.-P.P. and Y.-Q.D.; formal analysis, Q.L., P.-X.L., Y.X., Z.-F.Y., J.-P.C. and L.-P.P.; investigation, Q.L., P.-X.L., Z.-F.Y. and Y.-Q.D.; writing—original draft preparation, Q.L. and P.-X.L.; writing—review and editing, D.-L.H.; supervision, Y.-X.L. and D.-L.H.; project administration, Y.-X.L.; funding acquisition, Q.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (32160762), the Central Leading Local Science and Technology Development Funds Project (ZY24212009), the Guangxi Key Research and Development Programme (AB19245005), the Science and Technology Major Project of Guangxi (AA17202019), and the Fund of GXAAS (2020YT039).

Data Availability Statement

All data generated or analyzed during this study are included in this published article.

Conflicts of Interest

Author Zhuo-Fan Yao was employed by the company Guangxi Guiping Xishan Bishui Tea Garden Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Horticulturae 11 00423 g001
Figure 1. Impact of different selenium treatments on soil selenium availability. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
Figure 1. Impact of different selenium treatments on soil selenium availability. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
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Figure 2. Impact of different selenium treatments on selenium content in spring tea. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
Figure 2. Impact of different selenium treatments on selenium content in spring tea. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
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Horticulturae 11 00423 g003
Figure 3. Impact of different selenium treatments on GSH-Px activity in spring tea. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
Figure 3. Impact of different selenium treatments on GSH-Px activity in spring tea. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
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Figure 4. Impact of different selenium treatments on polyphenol content (A), free amino acid content (B), and polyphenol-to-amino acid ratio (C) in spring tea. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
Figure 4. Impact of different selenium treatments on polyphenol content (A), free amino acid content (B), and polyphenol-to-amino acid ratio (C) in spring tea. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
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Figure 5. Impact of different selenium treatments on polysaccharide content. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
Figure 5. Impact of different selenium treatments on polysaccharide content. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
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Table 1. Physicochemical properties and selenium content of the soil.
Table 1. Physicochemical properties and selenium content of the soil.
Total
Nitrogen 		Total
Phosphorus		Total
Potassium		Available
Nitrogen		Available
Phosphorus		Available
Potassium		pH ValueOrganic
Matter		Total
Selenium
3.21 g·kg−11.46 g·kg−17.30 g·kg−1357.0 mg·kg−1535.1 mg·kg−1427.0 mg·kg−15.9071.6 g·kg−10.82 mg·kg−1
Table 2. Impact of different selenium treatments on soil selenium forms (%).
Table 2. Impact of different selenium treatments on soil selenium forms (%).
TreatmentsSOL-SeEX-SeFMO-SeOM-SeRES-Se
CK0.21 ± 0.03 dC4.59 ± 0.36 cC5.11 ± 0.16 aA64.26 ± 0.83 bB 25.84 ± 0.99 aA
Se1001.11 ± 0.10 cB11.34 ± 0.46 bB3.71 ± 0.11 bB65.70 ± 1.76 bAB 18.14 ± 1.28 bBC
Se2251.28 ± 0.08 bB12.65 ± 0.41 aA2.05 ± 0.21 cC64.74 ± 1.81 bAB 19.29± 1.24 bB
Se3001.64 ± 0.01 aA12.81 ± 0.13 aA1.14 ± 0.20 dD69.61 ± 1.03 aA 14.80 ± 0.84 cC
Note: Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
Table 3. Impact of different selenium treatments on soil enzyme activity.
Table 3. Impact of different selenium treatments on soil enzyme activity.
TreatmentsSucrase
(mg·g−1·d−1)		Urease
(µg·g−1·d−1)		Acid Phosphatase
(nmol·g−1·d−1)		Catalase
(mmol·g−1·d−1)
CK59.93 ± 1.76 cC1823.96 ± 153.95 aA44,397.19 ± 493.14 a91.13 ± 1.65 a
Se10078.55 ± 0.60 aA1742.31 ± 63.55 aA43,313.44 ± 1102.04 a92.74 ± 3.02 a
Se22571.12 ± 3.36 bB1368.20 ± 55.96 bB42,606.21 ± 3269.90 a94.57 ± 3.77 a
Se30062.55 ± 1.57 cC1183.33 ± 67.09 bB41,744.65 ± 1108.99 a93.16 ± 4.69 a
Note: “d” represents day [24 h]. Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
Table 4. Chlorophyll content in spring tea under different selenium treatments.
Table 4. Chlorophyll content in spring tea under different selenium treatments.
TreatmentsChlorophyll Content (mg·g−1)Chlorophyll a/
Chlorophyll b
Chlorophyll aChlorophyll bTotal Content of Chlorophyll
CK0.684 ± 0.005 dC 0.274 ± 0.009 cC 0.958 ± 0.014 dD 2.498 ± 0.067 aA
Se1000.722 ± 0.008 bB 0.306 ± 0.012 bB 1.028 ± 0.020 bB 2.364 ± 0.068 aA
Se2250.746 ± 0.007 aA 0.351 ± 0.005 aA 1.097 ± 0.006 aA2.123 ± 0.044 bB
Se3000.708 ± 0.010 cB 0.286 ± 0.004 cBC 0.994 ± 0.006 cC 2.476 ± 0.070 aA
Note: Lowercase letters denote significant differences at p < 0.05 threshold, whereas uppercase letters represent highly significant differences at p < 0.01 threshold.
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Liao, Q.; Liang, P.-X.; Xing, Y.; Yao, Z.-F.; Chen, J.-P.; Pan, L.-P.; Deng, Y.-Q.; Liu, Y.-X.; Huang, D.-L. Optimizing Selenium Application for Enhanced Quality and Nutritional Value of Spring Tea (Camellia sinensis). Horticulturae 2025, 11, 423. https://doi.org/10.3390/horticulturae11040423

AMA Style

Liao Q, Liang P-X, Xing Y, Yao Z-F, Chen J-P, Pan L-P, Deng Y-Q, Liu Y-X, Huang D-L. Optimizing Selenium Application for Enhanced Quality and Nutritional Value of Spring Tea (Camellia sinensis). Horticulturae. 2025; 11(4):423. https://doi.org/10.3390/horticulturae11040423

Chicago/Turabian Style

Liao, Qing, Pan-Xia Liang, Ying Xing, Zhuo-Fan Yao, Jin-Ping Chen, Li-Ping Pan, Yao-Qiu Deng, Yong-Xian Liu, and Dong-Liang Huang. 2025. "Optimizing Selenium Application for Enhanced Quality and Nutritional Value of Spring Tea (Camellia sinensis)" Horticulturae 11, no. 4: 423. https://doi.org/10.3390/horticulturae11040423

APA Style

Liao, Q., Liang, P.-X., Xing, Y., Yao, Z.-F., Chen, J.-P., Pan, L.-P., Deng, Y.-Q., Liu, Y.-X., & Huang, D.-L. (2025). Optimizing Selenium Application for Enhanced Quality and Nutritional Value of Spring Tea (Camellia sinensis). Horticulturae, 11(4), 423. https://doi.org/10.3390/horticulturae11040423

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