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Article

Exogenous Application of Nano-Silicon and Melatonin Ameliorates Salinity Injury in Coix Seedlings

by
Beibei Qi
1,
Junkai Liu
2,
Ruixue Zheng
2,
Jiada Huang
1,* and
Chao Wu
2,*
1
College of Agriculture, Guangxi University, Nanning 530004, China
2
Guangxi Institute of Botany, Chinese Academy of Sciences, Guilin 541006, China
*
Authors to whom correspondence should be addressed.
Agronomy 2025, 15(8), 1862; https://doi.org/10.3390/agronomy15081862
Submission received: 25 June 2025 / Revised: 30 July 2025 / Accepted: 30 July 2025 / Published: 31 July 2025
(This article belongs to the Special Issue Harnessing Exogenous Applications for Crop Stress Tolerance and Enhanced Productivity)
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Abstract

Soil salinization is a major environmental constraint that poses a significant threat to global agricultural productivity and food security. Coix lacryma-jobi L., a minor cereal crop that is valued for its nutritional and medicinal properties, displays moderate susceptibility to salinity stress. Although exogenous treatments have been demonstrated to enhance plant resilience against various biotic and abiotic stresses, the potential of nano-silicon (NaSi), melatonin (MT), and their combined application in mitigating salinity-induced damage, particularly in relation to the medicinal properties of this medicinal and edible crop, remains poorly understood. This study investigated the effects of exogenous NaSi and MT application on Coix under salinity stress using two varieties with contrasting salinity tolerances. The plants were subjected to salinity stress and treated with NaSi, MT, or a combination of both. The results revealed that salinity stress significantly impaired the agronomic traits, physiological performance, and accumulation of medicinal compounds of Coix. Exogenous MT application effectively alleviated salinity-induced damage to agronomic and physiological parameters, exhibiting superior protective effects compared to NaSi treatment. Strikingly, the combined application of MT and NaSi demonstrated synergistic effects, leading to substantial improvements in growth and physiological indices. However, the medicinal components were only marginally affected by exogenous treatments under both control and salinity-stressed conditions. Further clarification of the molecular mechanisms underlying salinity stress responses and exogenous substance-induced effects is critical to achieving a comprehensive understanding of these protective mechanisms.

1. Introduction

Coix lacryma-jobi L., an annual or perennial herbaceous species belonging to the Gramineae family, has long been cultivated as both a cereal and medicinal crop across Asia [1]. Coix has a long-standing history of application in Traditional Chinese Medicine and has been officially listed in China’s medicinal and edible homology catalog [2]. As an edible minor cereal crop with notable nutritional and medicinal value, Coix is rich in diverse proteins, polysaccharides, and bioactive compounds and has traditionally been utilized for its anti-inflammatory, anti-cancer, and immunomodulatory properties [3,4]. Soil salinization has been increasingly exacerbated worldwide, primarily driven by inappropriate irrigation practices and industrial activities [5,6]. It was reported that over 1.0 billion hectares of land worldwide are affected by salinity stress, with approximately 7% of land area and 33% of irrigated lands experiencing severe salinization [7]. Salinity stress disrupts plant ion homeostasis, triggers osmotic stress, and leads to excessive accumulation of reactive oxygen species, consequently impairing photosynthesis, stunting growth, and diminishing crop productivity [8,9]. Mitigating salinity-induced injuries is therefore critical for global food security and sustainable agricultural development.
Generally, most gramineous plants are relatively salinity-susceptible, with their growth and yield being significantly impaired under saline conditions [10]. Salinity stress has been shown to significantly inhibit the growth of Coix seedlings [11]. Exploring effective approaches to enhance salinity tolerance, such as the development of crop varieties with improved salinity tolerance [12], optimization of cultivation practices, and implementation of regulatory measures, is of considerable practical significance. However, progress in developing and releasing novel Coix varieties remains constrained, and there persists a pronounced scarcity of salinity-stress-tolerant Coix varieties. Currently, exogenous application of bioactive substances has emerged as a promising approach to alleviate salinity stress in crops. Silicon (Si) [13] and melatonin (MT) [14] have garnered increasing attention due to their multifaceted roles in stress adaptation. MT has been recognized to act as a potent antioxidant and signaling molecule, scavenging reactive oxygen species, modulating phytohormone levels, and upregulating certain stress-responsive genes [15,16,17].
Nanoparticles (e.g., silica, carbon dots) function as carriers for fertilizers, pesticides, and growth regulators, thereby offering innovative strategies to enhance crop productivity, reduce resource waste, and mitigate environmental impacts in modern agriculture. Nano-silicon (NaSi), a novel Si source with higher bioavailability than conventional Si fertilizers [18], is an important element for monocots’ normal growth and development. NaSi can improve plant stress resistance by stabilizing cell membranes, enhancing antioxidant capacity, and regulating ion transport [19], particularly in monocotyledonous gramineous plants. Previous studies have demonstrated the individual efficacy of NaSi and MT in mitigating biotic/abiotic stress in crops such as rice (Oryza sativa), wheat (Triticum aestivum), and tomato (Solanum lycopersicum) [20,21,22]. However, their roles in Coix, a medicinal and edible homology plant, under salinity stress remain largely unexplored, and the underlying mechanisms, e.g., crosstalk between NaSi and MT in regulating Coix growth, are yet to be clarified.
To address these knowledge gaps, the present study investigated the regulatory effects of exogenous NaSi and MT application on the growth of Coix plants under salinity stress. We hypothesized that both substances would alleviate salinity-induced damage in Coix plants, potentially exerting synergistic effects. The overarching objective is to provide theoretical underpinnings for optimizing Coix cultivation practices in saline soils and broadening the applicability of NaSi and MT in stress agriculture, thereby facilitating the sustainable utilization of saline–alkali soils and strengthening the economic viability of Coix-based agricultural systems.

2. Materials and Methods

2.1. Experimental Site, Plant Material, Germination, and Seedling Establishment

Hydroponic experiments were conducted at the Guangxi Institute of Botany, Chinese Academy of Science, Guilin city, Guangxi Province, China (25°4′ N, 110°18′ E), from September to November 2023. Two contrasting Coix varieties, the Qichun Coix variety (salinity-susceptible, originating from Qichun County, Huanggang city, Hubei Province) and the Shizhong Coix variety (salinity-tolerant, originating from Longyan city, Fujian Province), which had been approved as national geographic indication products in China, owing to their significant industrial advantages, high market recognition, and large-scale commercial production, were used in the current study.
To synchronize germination, Coix seeds were soaked in tap water for 12 h and incubated in a constant-temperature incubator (DHP-360, Saidelisi Technology Co., Ltd., Tianjin, China) at 37 °C in darkness after breaking dormancy at 45 °C for 6 h. On 5 September 2023, germinated seeds of each variety were sown into seedling trays (54 cm × 28 cm × 3.8 cm; 8 × 16 holes) filled with mixed soil substrates consisting of sandy soils and peat soils at a ratio of 2:1 [23] to facilitate seedling establishment. On 25 September 2023, uniformly grown seedlings were selected for hydroponic culture with Hoagland nutrient solution using 12 L black polypropylene tanks (27.5 cm × 24.5 cm × 18.0 cm) that were each covered with six PVC lids (12.0 cm × 8.5 cm) and contained a total of 36 holes for plant fixation. The seedlings were acclimated for 24 days, during which the nutrient solutions were renewed every 4 to 5 days.

2.2. Salinity Stress Treatment and Exogenous Chemical Application

In our previous study, Coix seedlings were subjected to a control treatment (Hoagland nutrient solution) and three salinity stress groups (Hoagland nutrient solution supplemented with 68.4 mmol L−1 NaCl, 136.8 mmol L−1 NaCl, and 205.1 mmol L−1 NaCl, respectively) for salinity tolerance evaluation. Observations revealed significant varietal variations in Coix seedlings under the 68.4 mmol L−1 NaCl salinity stress, which was therefore selected as the salinity stress level for the current study. The NaSi employed in the current study is a translucent aqueous solution (25~30% w/w silica content) with a particle size distribution of 10~30 nm and pH range of 9.0~12.0, purchased from XFNANO Materials Tech Co., Ltd. (Product No. XFI24; Nanjing, China), a leading manufacturer of nanomaterials in China with extensive applications [24]. MT was obtained from Macklin (Shanghai Macklin Biochemical Technology Co., Ltd., Shanghai, China). On 18 October 2023, the seedlings of the two examined Coix varieties were divided into eight treatment groups (Figure 1) as described below.
(1) Non-stressed control (CK): Hoagland nutrient solution; (2) MT application under CK: Hoagland nutrient solution supplemented with 100 μmol L−1 MT; (3) NaSi application under CK: Hoagland nutrient solution supplemented with 600 mg L−1 NaSi; (4) MT + NaSi application under CK: Hoagland nutrient solution supplemented with 100 μmol L−1 MT and 600 mg L−1 NaSi; (5) Salinity stress (ST): Hoagland nutrient solution supplemented with 68.4 mmol L−1 NaCl; (6) MT application under ST: Hoagland nutrient solution supplemented with 68.4 mmol L−1 NaCl and 100 μmol L−1 MT; (7) NaSi application under ST: Hoagland nutrient solution supplemented with 68.4 mmol L−1 NaCl and 600 mg L−1 NaSi; (8) MT + NaSi application under ST: Hoagland nutrient solution supplemented with 68.4 mmol L−1 NaCl, 100 μmol L−1 MT, and 600 mg L−1 NaSi. Each treatment was replicated three times. During the experiment, the nutrient solution was renewed every 4~5 days until 6 November 2023, on which processing ended.

2.3. Plant Measurements

Measurements of gas exchange parameters (e.g., photosynthetic rate) were conducted on the youngest fully expanded leaves using a LI-6400 portable photosynthesis system (LI-COR 6400, Lincoln, NE, USA) equipped with light and CO2 control modules on 5 November 2023. Prior to measurement, the sampled leaves were exposed to natural light for 20 min to facilitate stomatal opening. The block temperature was set at 25 °C, and the CO2 concentration in the cuvette was maintained at ambient levels. The air flow rate was maintained at 500 μmol s−1. To minimize external interference, the air inlet of the LI-6400 was connected to a 2~3 m plastic tube, with the tube end being positioned away from the operator [25,26].
The plant height was measured with a ruler, which involved determining the distance from the top of the blade to the stem base of the stretched plants. The leaf nitrogen concentration and SPAD value were quantified using a portable plant nutrition analyzer (TYS-4N, Zhejiang TOP Cloud-agri. Technology Co., Ltd., Hangzhou, China). The shoots were harvested and dried to a constant weight in an oven (101-0, Shaoxing Supe Instrument Co., Ltd., Shaoxing, China) at 105 °C and then weighed to calculate the aboveground biomass [23].
The roots were rinsed with tap water, and fresh white roots were collected and immediately stored at −80 °C. The extraction and quantification of coixol in Coix roots were carried out in accordance with the methods reported in our previous study [23], utilizing high-performance liquid chromatography (HPLC, Shimadzu LC-16, Shimadzu Co., Ltd., Kyoto, Japan). Briefly, 0.2 g of root tissue was ground in 5 mL of cold extraction buffer (100% methanol, Sinopharm Chemical Reagent Co., Ltd., Shanghai, China). The homogenates were transferred to 10 mL centrifuge tubes, subjected to ultrasonic extraction for 1 h in an ice-water bath, and then centrifuged at 10,000× g for 10 min. The supernatants were collected, and the pellets were re-extracted using the same procedure. The supernatants were pooled, and 10 mL of the mixture was filtered through a 0.45 μm organic microporous filter membrane.
The diluted solution was subjected to separation via HPLC equipped with a C18 column (WondaCract ODS-2 C18 column; 250 mm × 4.6 mm, 5 μm) through isocratic elution with a mobile phase composed of 25% acetonitrile (purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) and 75% ddH2O for a duration of 20 min at a flow rate of 0.9 mL min−1. The column temperature was maintained at a constant 25 °C, and UV detection was carried out at 232 nm. Calibration standards were formulated at concentrations of 3, 5, 7, 10, 15, 20, and 25 ng mL−1 of the coixol standard, and a standard curve was subsequently generated. The coixol concentration in the Coix root samples was determined in accordance with the derived standard curve and expressed in units of mg g−1 fresh weight.

2.4. Statistical Analysis

The experiments were conducted using a completely randomized design with a 2 × 2 × 4 factorial arrangement (two varieties, two salinity treatments, and four exogenous treatments), resulting in 16 treatments with 3 replicates each. The Shapiro–Wilk normality test was performed using GraphPad Prism (version 10.0, GraphPad Software, Inc., La Jolla, CA, USA) to assess the normality of the variables. A significance level of p > 0.05 indicated compliance with normality assumptions. Variables were transformed, if necessary, using the most appropriate transformation from several tested methods. An analysis of variance (ANOVA) was performed for all variables across salinity treatments, exogenous substance treatments, and varieties using Statistix 9.0 (Analytical Software, Tallahassee, FL, USA).
The ANOVA results revealed significant effects of salinity treatments, exogenous substance treatments, varieties, and their interactions on most variables at the p < 0.05 significance level. The present study focuses on the effects of exogenous substance applications under salinity stress conditions, and thus, interaction effects were not the primary concern of this investigation. Tukey’s honestly significant difference (Tukey HSD) test [27] was employed at the p < 0.05 and p < 0.01 level, respectively, to further examine the differences among salinity and exogenous substance treatments. Specifically, for each variety, comparisons were carried out across salinity and exogenous substance treatments. Figures were generated using the ggplot2 package [28] in R Foundation for Statistical Computing (ver. 4.4.2 Analytical Software, https://www.R-project.org/ (accessed on 31 October 2024); R Core Team, Vienna, Austria) and Microsoft Visio 2013 (Microsoft Corporation, Washington, DC, USA).

3. Results

3.1. Effects of Exogenous Substances on Plant Height and Biomass Under Salinity Stress

As shown in Figure 2 and Figure 3, salinity treatment led to statistically significant reductions in plant height and aboveground biomass of the Qichun Coix variety by 64.2% and 90.0%, respectively, whereas no notable effects were observed in the Shizhong Coix variety. Under normal conditions, exogenous substances (MT, NaSi, and their combination) exerted negligible effects on plant height and aboveground biomass in both Coix varieties. However, under salinity stress conditions, compared with the NC treatment, exogenous application of MT, NaSi, and their combination significantly increased plant height and aboveground biomass in the Qichun Coix variety. Among these treatments, MT alone and the MT + NaSi combination exerted more pronounced effects on plant height and aboveground biomass than NaSi application.

3.2. Effects of Exogenous Substances on Photosynthesis Under Salinity Stress

Compared to the NC treatment, salinity stress induced pronounced reductions in photosynthetic rate (A), intercellular CO2 concentration (Ci), and transpiration rate (E) for the two adopted Coix varieties, with more severe adverse effects being observed in Qichun Coix than in Shizhong Coix (Table 1). Under most conditions, exogenous substance applications (MT, NaSi, and their combination) enhanced photosynthesis parameters at a significant level, especially under salinity stress, except for stomatal conductance (gs). Exogenous substance applications demonstrated a more pronounced mitigating effect against salinity-induced injuries in Qichun Coix (average 205.8%) compared to Shizhong Coix (average 47.0%). Additionally, MT (156.7%) and the MT + NaSi combination (average 173.7%) treatments exerted stronger enhancing effects on A than NaSi treatment (average 48.7%).

3.3. Effects of Exogenous Substances on Physiological Traits Under Salinity Stress

Salinity treatment significantly decreased SPAD values, leaf nitrogen concentration, and leaf water content, while elevating the relative conductivity in the Coix varieties (Table 2). Notably, Qichun Coix displayed more pronounced variations in most parameters compared to Shizhong Coix. Application of exogenous substances (MT, NaSi, and their combination) effectively mitigated salinity-induced damage in both Coix varieties. The tested physiological traits exhibited a consistent trend, as the combined treatment of MT and NaSi exerted the most substantial alleviating effects, followed by melatonin application alone, whereas NaSi application showed the weakest effect.

3.4. Effects of Exogenous Substances on Root Coixol Content Under Salinity Stress

As shown in Figure 4, salinity stress significantly reduced the coixol concentration in roots of Coix plants. Specifically, salinity treatment reduced root coixol by 62.9% in the Qichun Coix variety and 49.2% in the Shizhong Coix variety, respectively. The application of exogenous substances (MT, NaSi, and their combination) showed an increasing trend in coixol concentration within Coix roots; however, this effect did not reach statistical significance in either adopted Coix variety.

4. Discussion

Soil salinization has emerged as a crucial restraint in the context of sustainable agricultural development [6]. China, ranking among the countries that are most severely affected by salinization, currently possesses a total area of approximately 9.9 × 107 hectares of saline–alkali land, which accounts for 10% of the global total [29]. The continued expansion of such lands has consequently impaired plant growth, thereby posing a substantial threat to crop yield and quality [30]. In the current study, salinity treatment not only reduced agronomic (plant height, aboveground biomass) (Figure 1, Figure 2 and Figure 3) and physiological parameters (photosynthesis, relative conductivity, leaf nitrogen concentration, etc.) (Table 1 and Table 2), but also impaired the medicinal quality in Coix varieties (Figure 4). Notably, the Shizhong Coix variety exhibited relatively less salinity-induced injury compared to the Qichun Coix variety.
In staple crops such as rice, wheat, and maize, salinity stress frequently causes stunted plant growth and drastic biomass reduction [31,32,33,34] through diverse mechanisms, encompassing physiological, metabolic, and molecular processes [35]. For instance, alterations in root cell membrane permeability lead to impaired water uptake; and disruption of ionic homeostasis not only perturbs enzyme activity but also inhibits photophosphorylation and impedes electron transport in the respiratory chain, ultimately culminating in phenotypic manifestations such as stunted plant development and a marked reduction in biomass [9,36,37]. Previous studies have proposed the development of crop varieties with enhanced salinity tolerance [12]; however, the progress in developing and releasing novel Coix varieties remains constrained, and there is a deficiency in salinity-stress-tolerant Coix varieties. Combined with the present study and our prior observations, it was proposed that the Shizhong (Pu) Coix variety may emerge as a relatively promising cultivar, due to its better adaptability than other Coix varieties [23].
Exogenous substance application has been proven to enhance crops’ tolerance to diverse biotic and abiotic stresses [38]. Si confers protective effects against environmental stresses [39,40], particularly in gramineous crops. Characterized by superior specificity, reactivity, bioactivity, and adherence compared to bulk Si, NaSi exhibits eco-friendly properties and holds promise for mitigating stress impacts while enhancing plant tolerance to both abiotic and biotic stresses [41,42]. In the present study, exogenous NaSi application alleviated salinity-induced damage to agronomic traits (Figure 2 and Figure 3) and physiological parameters such as photosynthesis, SPAD values, leaf nitrogen concentration, and leaf water content (Table 1 and Table 2) across the two tested Coix varieties, with Qichun Coix varieties exhibiting more pronounced ameliorative effects. Previous studies demonstrated that NaSi alleviated salinity stress in plants through a multi-faceted mechanism involving physiological regulation and molecular modulation.
For instance, exogenous nanoparticles, including NaSi, alleviated salinity stress by increasing the K+ concentration, antioxidant activities, and non-enzymatic compounds and decreasing the Na+ concentration, lipid peroxidation, electrolyte leakage, and reactive oxygen species production across diverse plant species (e.g., tomato, strawberry, lupine, and soybean) [19,42,43,44,45]. In rice plants, silicon supplementation alleviated salinity injury by upregulating silicon uptake genes (Lsi1, Lsi2) under saline conditions, likely via jasmonic acid-mediated signaling pathways [40]. It is worth noting that different NaSi formulations exert differential effects on morphological and biochemical traits, with functionalized silica nanoparticles outperforming their non-functionalized counterparts under saline conditions in lupine species [42]. The discrepancies in salinity stress alleviation may be attributed to interspecific variability in physiological responsiveness, silicon particle type, and morphological properties, as well as application methods and concentration gradients. Taken together, our results confirmed that exogenous NaSi application can partially mitigate salinity-induced growth inhibition in Coix varieties.
As an indoleamine compound that is ubiquitously distributed in both animals and plants, MT functions dually as a hormonal signaling molecule and an antioxidant in regulating plant stress resistance mechanisms [15,16,21]. In the current study, exogenous MT application effectively alleviated salinity-induced injury to agronomic traits and physiological parameters of Coix plants, with a more pronounced effect than NaSi application (Figure 2 and Figure 3; Table 1 and Table 2). Consistent with these findings, exogenous MT application has been demonstrated to enhance salinity stress tolerance across various plant species including rice, Malus zumi, and cucumber [17,20,46]. Mechanistically, MT enhances plant stress tolerance through synergistic regulation of antioxidant enzyme activities, ATPase function, and Na+ and K+ homeostasis [46]. Genes encoding NADPH oxidases (OsRBOHF, OsRBOHA) and potassium transporters (OsHAK1, OsHAK5, OsAKT1) were upregulated by exogenous MT under salinity stress [47]. In terms of photosynthetic performance, MT influences stomatal morphology and improves photosynthetic efficiency [48], which helps maintain carbon assimilation under salinity stress.
Furthermore, the combined application of MT and NaSi exhibited pronounced synergistic effects, with most agronomic and physiological parameters showing notable enhancements (Figure 2 and Figure 3; Table 1 and Table 2). This synergism is consistent with previous cross-species studies, where co-application of MT and Si was reported to mitigate salinity stress or heavy metal (e.g., chromium, cadmium)-stress-induced damage in rice [49], maize [50], Brassica napus [51], and Apium graveolens [52]. Mechanistically, such synergistic protection may be mediated through multi-dimensional regulatory networks: (i) enhancement of the antioxidative defense system via upregulating key enzymes and non-enzymatic antioxidants; (ii) modulation of endogenous phytohormone metabolism; (iii) improvement of photosynthetic traits by maintaining chloroplast structure and enhancing PSII efficiency; and (iv) regulation of ion homeostasis to reduce toxic ion accumulation [49,51,52]. These integrated physiological mechanisms collectively contribute to the observed stress tolerance enhancement. The molecular and metabolomic mechanisms underlying the regulation by exogenous substances require in-depth investigation.
Notably, while exogenous application of phytohormones (e.g., salicylic acid) has been shown to enhance the production of medicinal components in Mucuna macrocarpa [53], the current study observed that MT, NaSi, and their combined application exerted negligible effects on medicinal components under both non-stressed and salinity-stressed conditions (Figure 4). These discrepancies are hypothesized to be potentially associated with factors such as species specificity, types of exogenous substances, and application methodologies. Collectively, our findings indicate that exogenous applications of MT, NaSi, and their combination enhance the tolerance to salinity stress in Coix varieties. However, while hydroponic results demonstrate the potential of NaSi and MT to alleviate salinity-induced damage at the physiological level, their efficacy in soils with complex salt profiles under field conditions requires further validation. Consequently, follow-up experiments are proposed, including potting soil trials with graded salinity levels (mimicking field conditions) and field plot studies in saline–alkaline regions, focusing on pharmaceutical metabolite accumulation (e.g., polysaccharides, coixenolide) and critical yield parameters for commercial viability.

5. Conclusions

Salinity stress induced significant reductions in the agronomic traits, physiological parameters, and medicinal components of Coix plants. Exogenous application of MT effectively alleviated salinity-induced damage to these agronomic and physiological indicators, with a more pronounced protective effect compared to NaSi treatment. Notably, the combined application of MT and NaSi exhibited pronounced synergistic effects, resulting in marked improvements in agronomic and physiological indices. In contrast, the medicinal components were marginally influenced by exogenous treatments under both non-stressed and salinity-stressed conditions.

Author Contributions

C.W. designed the experiments. B.Q. and J.L. performed the experiments. B.Q., J.L., R.Z., C.W. and J.H. analyzed the data, wrote the manuscript, and revised the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Bagui Young Top-notch Talents Project, the Science and Technology Major Project of Guangxi, China (grant no. Guike AA22096020), and the Fund of Guangxi Key Laboratory of Plant Functional Phytochemicals and Sustainable Utilization (ZRJJ2024-16).

Data Availability Statement

The datasets presented in this study are included in the main text.

Acknowledgments

We acknowledge the anonymous reviewers for their constructive comments, which greatly improved the quality of this paper. All authors have read and agreed to the published version of the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Illustration of exogenous substances on Coix seedlings under salinity stress. CK, non-stressed control; ST, salinity stress; NC, non-exogenous substances; ET, exogenous treatments; MT, melatonin; NaSi, nano-silicon; MT + NaSi, combined application of melatonin and nano-silicon.
Figure 1. Illustration of exogenous substances on Coix seedlings under salinity stress. CK, non-stressed control; ST, salinity stress; NC, non-exogenous substances; ET, exogenous treatments; MT, melatonin; NaSi, nano-silicon; MT + NaSi, combined application of melatonin and nano-silicon.
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Figure 2. Effects of exogenous substances on plant height of Coix under salinity treatments. Different letters indicate significant differences among the exogenous treatments under salinity conditions at the p < 0.05 level within the Qichun and Shizhong Coix varieties, respectively, according to the Tukey HSD test. CK, non-stressed control; ST, salinity stress; NC, non-exogenous substances; ET, exogenous treatments; MT, melatonin; NaSi, nano-silicon; MT + NaSi, combined application of melatonin and nano-silicon.
Figure 2. Effects of exogenous substances on plant height of Coix under salinity treatments. Different letters indicate significant differences among the exogenous treatments under salinity conditions at the p < 0.05 level within the Qichun and Shizhong Coix varieties, respectively, according to the Tukey HSD test. CK, non-stressed control; ST, salinity stress; NC, non-exogenous substances; ET, exogenous treatments; MT, melatonin; NaSi, nano-silicon; MT + NaSi, combined application of melatonin and nano-silicon.
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Figure 3. Effects of exogenous substances on aboveground biomass of Coix under salinity treatments. Different letters indicate significant differences among the exogenous treatment under salinity treatments at the p < 0.05 level within the Qichun and Shizhong Coix varieties, respectively, according to the Tukey HSD test. CK, non-stressed control; ST, salinity stress; NC, non-exogenous substances; ET, exogenous treatments; MT, melatonin; NaSi, nano-silicon; MT + NaSi, combined application of melatonin and nano-silicon.
Figure 3. Effects of exogenous substances on aboveground biomass of Coix under salinity treatments. Different letters indicate significant differences among the exogenous treatment under salinity treatments at the p < 0.05 level within the Qichun and Shizhong Coix varieties, respectively, according to the Tukey HSD test. CK, non-stressed control; ST, salinity stress; NC, non-exogenous substances; ET, exogenous treatments; MT, melatonin; NaSi, nano-silicon; MT + NaSi, combined application of melatonin and nano-silicon.
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Figure 4. Effects of exogenous substances on root coixol under salinity treatments. Different letters indicate significant differences among the exogenous treatment under salinity treatments at the p < 0.05 level within the Qichun and Shizhong Coix varieties, respectively, according to the Tukey HSD test. CK, non-stressed control; ST, salinity stress; NC, non-exogenous substances; ET, exogenous treatments; MT, melatonin; NaSi, nano-silicon; MT + NaSi, combined application of melatonin and nano-silicon.
Figure 4. Effects of exogenous substances on root coixol under salinity treatments. Different letters indicate significant differences among the exogenous treatment under salinity treatments at the p < 0.05 level within the Qichun and Shizhong Coix varieties, respectively, according to the Tukey HSD test. CK, non-stressed control; ST, salinity stress; NC, non-exogenous substances; ET, exogenous treatments; MT, melatonin; NaSi, nano-silicon; MT + NaSi, combined application of melatonin and nano-silicon.
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Table 1. Effects of exogenous substances on photosynthesis of Coix under salinity treatments.
Table 1. Effects of exogenous substances on photosynthesis of Coix under salinity treatments.
VarietySalinity TreatmentExogenous TreatmentA
(μmol m−2 s−1)		gs
(mol m−2 s−1)		Ci
(μmol mol−1)		E
(mmol m−2 s−1)
Qichun CoixCKNC11.4 ± 0.69 c0.10 ± 0.00 a132 ± 9.50 ab1.22 ± 0.02 c
MT14.6 ± 0.97 b0.11 ± 0.00 a97.8 ± 22.2 ab2.36 ± 0.12 ab
NaSi11.2 ± 0.86 c0.10 ± 0.00 a131 ± 14.6 ab1.82 ± 0.11 bc
MT + NaSi17.1 ± 0.29 a0.13 ± 0.01 a78.0 ± 24.9 ab2.98 ± 0.24 a
STNC3.44 ± 0.53 e0.04 ± 0.02 b155 ± 41.0 a1.17 ± 0.46 c
MT12.3 ± 0.57 bc0.10 ± 0.02 a82.5 ± 38.4 ab3.06 ± 0.61 a
NaSi5.95 ± 0.33 d0.04 ± 0.01 b84.3 ± 37.3 ab1.37 ± 0.19 c
MT + NaSi13.3 ± 0.76 bc0.10 ± 0.01 a62.9 ± 29.5 b3.16 ± 0.33 a
Shizhong CoixCKNC13.2 ± 0.73 cd0.10 ± 0.00 a104 ± 13.7 a1.54 ± 0.08 d
MT17.2 ± 0.90 ab0.12 ± 0.01 a71.0 ± 4.11 abc2.66 ± 0.10 abc
NaSi15.4 ± 0.98 bc0.12 ± 0.02 a83.8 ± 19.6 ab2.16 ± 0.00 cd
MT + NaSi19.6 ± 0.57 a0.14 ± 0.01 a51.1 ± 6.21 bc3.14 ± 0.15 ab
STNC9.11 ± 0.34 e0.06 ± 0.00 a39.7 ± 15.4 c1.70 ± 0.06 d
MT14.2 ± 1.01 bcd0.36 ± 0.44 a54.2 ± 3.82 bc3.18 ± 0.32 a
NaSi11.3 ± 1.85 de0.08 ± 0.02 a49.6 ± 17.3 bc2.33 ± 0.56 bcd
MT + NaSi14.6 ± 0.80 bcd0.10 ± 0.01 a55.5 ± 16.6 bc3.43 ± 0.20 a
A, photosynthetic rate; gs, stomatal conductance; E, transpiration rate; Ci, intercellular CO2 concentration. The values are shown as the means ± SDs (n = 3). Different letters indicate significant differences among the exogenous treatment under salinity treatments at the p < 0.05 level within the Qichun Coix and Shizhong Coix varieties, respectively, according to the Tukey HSD test. CK, non-stressed control; ST, salinity stress; NC, non-exogenous substances; MT, melatonin; NaSi, nano-silicon; MT + NaSi, combined application of melatonin and nano-silicon.
Table 2. Effects of exogenous substances on physiological traits of Coix variety under salinity treatments.
Table 2. Effects of exogenous substances on physiological traits of Coix variety under salinity treatments.
VarietySalinity TreatmentExogenous TreatmentSPADLeaf Nitrogen ConcentrationRelative ConductivityLeaf Water Content (%)
Qichun CoixCKNC39.6 ± 0.67 bc12.4 ± 0.20 bc0.14 ± 0.01 b85.8 ± 2.47 a
MT46.6 ± 2.57 a14.9 ± 0.81 a0.12 ± 0.03 b83.0 ± 2.11 a
NaSi36.6 ± 1.49 c11.5 ± 0.44 c0.12 ± 0.03 b84.9 ± 0.27 a
MT + NaSi50.1 ± 0.91 a15.6 ± 0.31 a0.10 ± 0.01 b85.0 ± 1.82 a
STNC15.9 ± 0.62 e5.3 ± 0.15 e0.45 ± 0.23 a60.8 ± 2.87 c
MT41.4 ± 1.64 b13.0 ± 0.47 b0.18 ± 0.08 b83.4 ± 0.90 a
NaSi22.2 ± 2.21 d7.2 ± 0.66 d0.27 ± 0.07 ab69.0 ± 1.57 b
MT + NaSi46.7 ± 1.46 a14.6 ± 0.40 a0.22 ± 0.05 ab84.1 ± 1.34 a
Shizhong CoixCKNC48.9 ± 2.11 abc15.2 ± 0.67 abc0.11 ± 0.03 bc85.8 ± 1.53 a
MT52.8 ± 1.64 ab16.4 ± 0.46 ab0.08 ± 0.03 c83.8 ± 2.58 a
NaSi47.6 ± 2.48 bc14.8 ± 0.76 bc0.09 ± 0.02 c84.2 ± 1.62 a
MT + NaSi53.2 ± 2.86 a16.5 ± 0.85 a0.11 ± 0.01 bc85.0 ± 0.89 a
STNC34.2 ± 1.87 e10.8 ± 0.53 e0.35 ± 0.18 a77.8 ± 1.79 b
MT44.1 ± 0.65 cd13.8 ± 0.20 cd0.32 ± 0.06 ab82.8 ± 3.22 ab
NaSi39.1 ± 1.88 de12.3 ± 0.56 de0.27 ± 0.08 abc81.9 ± 2.66 ab
MT + NaSi50.7 ± 0.51 ab15.7 ± 0.15 ab0.21 ± 0.03 abc85.0 ± 0.85 a
The values are shown as the means ± SDs (n = 3). Different letters indicate significant differences among the exogenous treatments under salinity treatments at the p < 0.05 level within the Qichun Coix and Shizhong Coix varieties, respectively, according to the Tukey HSD test. CK, non-stressed control; ST, salinity stress; NC, non-exogenous substances; MT, melatonin; NaSi, nano-silicon; MT + NaSi, combined application of melatonin and nano-silicon.
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Qi, B.; Liu, J.; Zheng, R.; Huang, J.; Wu, C. Exogenous Application of Nano-Silicon and Melatonin Ameliorates Salinity Injury in Coix Seedlings. Agronomy 2025, 15, 1862. https://doi.org/10.3390/agronomy15081862

AMA Style

Qi B, Liu J, Zheng R, Huang J, Wu C. Exogenous Application of Nano-Silicon and Melatonin Ameliorates Salinity Injury in Coix Seedlings. Agronomy. 2025; 15(8):1862. https://doi.org/10.3390/agronomy15081862

Chicago/Turabian Style

Qi, Beibei, Junkai Liu, Ruixue Zheng, Jiada Huang, and Chao Wu. 2025. "Exogenous Application of Nano-Silicon and Melatonin Ameliorates Salinity Injury in Coix Seedlings" Agronomy 15, no. 8: 1862. https://doi.org/10.3390/agronomy15081862

APA Style

Qi, B., Liu, J., Zheng, R., Huang, J., & Wu, C. (2025). Exogenous Application of Nano-Silicon and Melatonin Ameliorates Salinity Injury in Coix Seedlings. Agronomy, 15(8), 1862. https://doi.org/10.3390/agronomy15081862

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