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Article

Effect of Lighting Type on the Nitrates Concentration, Selective Bioactive Compounds and Yield of Sweet Basil (Ocimum basilicum L.) in Hydroponic Production

by
Małgorzata Mirgos
1,*,
Anna Geszprych
1,
Jarosław L. Przybył
1,
Monika Niedzińska
1,
Marzena Sujkowska-Rybkowska
2,*,
Janina Gajc-Wolska
1 and
Katarzyna Kowalczyk
1
1
Department of Vegetable and Medicinal Plants, Institute of Horticulture Sciences, Warsaw University of Life Sciences, Nowoursynowska 159, 02-776 Warsaw, Poland
2
Department of Botany, Institute of Biology, Warsaw University of Life Sciences, Nowoursynowska 159, 02-776 Warsaw, Poland
*
Authors to whom correspondence should be addressed.
Agronomy 2025, 15(4), 966; https://doi.org/10.3390/agronomy15040966
Submission received: 24 March 2025 / Revised: 9 April 2025 / Accepted: 11 April 2025 / Published: 16 April 2025
(This article belongs to the Special Issue Advanced Hydroponics Technology for Vegetable Production: New Opportunities and Challenges)
Browse Figures
Versions Notes

Abstract

:
The effect of lighting basil with LED DR/B LB (Light Emitting Diode deep red/blue low blue) lamps throughout the cultivation cycle or for only 7 days before harvest, after the period of using HPS (High Pressure Sodium) lamps, was studied in comparison with the use of HPS lamps only, at the same light intensity. Plants of two Genovese type basil cultivars, recommended for pot and hydroponic cultivation, were used for the experiment. Plant growth observations were made and herb and leaf yields, dry matter, nitrates, potassium, phosphorus, calcium, total sugars, total soluble solids, ascorbic acid, chlorophylls, and carotenoids were determined. Plants of both tested basil cultivars grown under LED lighting were characterized by a higher content of ascorbic acid, carotenoids, and sugars and a lower content of nitrates than those grown under HPS lights. In plants grown under LED lighting only, nitrate content was on average 31% lower than under HPS lamps. The use of LEDs for the last 7 days of cultivation resulted in a significant reduction in nitrate content in only one of the studied cultivars. Further research on the effect of lighting type on sweet basil yield and quality, depending on other factors, both genetic and environmental, is recommended.

1. Introduction

Sweet basil (Ocimum basilicum L.) is a popular spice plant with aromatic, tender leaves used for culinary purposes around the world. It is native to the tropical regions of South Asia and Africa, so it is a thermophilic plant and the best way to obtain it in cooler climates is to grow it in a greenhouse [1]. Like lettuce, spinach, and other leafy vegetables, basil is increasingly being grown in hydroponic systems [2], such as Nutrient Film Technique (NFT). This technology is widely recognized as beneficial for the growth and yield of vegetables and herbs [3], and it offers the possibility of indoor production, where the proper selection of the light source and quality of the light spectrum is of particular importance [4]. Greenhouse and indoor light-based crops are expected to play an important role in meeting the growing demand for food in the future [5].
Studies conducted on lettuce indicate that the most intensive plant growth is observed at the light intensity of 200 µmol × m−2 × s−1 [6]. Results presented by Rahman et al. [7] indicate that satisfactory basil yield can be obtained at PPFD of 155 μmol × m−2 × s−1, but as reported by Larsen et al. [8], increasing PPFD up to 300 μmol × m−2 × s−1 increases fresh weight, dry matter content, and height of basil plants. Production efficiency can also be improved based on daily light integral (DLI), mean daily temperature MDT, appropriate photoperiod or CO2 supplementation other environmental factors to achieve the desired growth and energy use efficiency results [9,10,11,12]. Pan et al. [13] show that the combination of increased CO2 and increased light intensity has a synergistic effect on plant growth by increasing the efficiency of photosynthesis and the efficiency of water use, light energy, and CO2 fixation. Singh et al. [14] also reported that CO2 supplementation has significant potential to increase the growth and development of green leafy vegetables, including basil, grown in NFT systems. Plant growth depends largely on the spectral composition of light [15]. Plant lighting technologies are rapidly developing, and LED (Light Emitting Diode) lamps for indoor cultivation are often designed to optimize the emission of photosynthetically active radiation (PAR) (mainly in the red and blue light ranges) to achieve satisfactory yields, which is economically and energetically preferable [16]. The use of new LED lighting technologies with a wide variety and dynamic control of the spectral composition and total radiation levels would allow the growth and quality of the plants grown to be optimized [17]. There are reports on the effect of LED light of different spectra on the growth of basil, both in typical hydroponic and vertical systems [15,18,19]. The study on basil cultivation also indicates that a higher proportion of blue light compared to red light leads to higher yields. Moreover, the use of blue light with a peak wavelength of 435 nm was 20% more effective in improving basil growth than blue light with a peak wavelength of 450 nm [20], while Solbach et al. [15] reported that red or white light in combination with far-red light is more efficient in plant dry matter production than blue light. In contrast, the results of experiments by Larsen et al. [8] indicate that a spectrum containing 9% blue, while the rest of the spectrum is 70% red and 19% green, can be maintained throughout the basil growth period, as the increased amount of blue does not improve the fresh weight of the plant or the dry matter content. Such inconsistent results make it difficult to predict the response of plants to the applied lighting not only in terms of biomass production but also in terms of plant chemical composition. A number of recent studies concerned the effect of LED light spectrum on growth parameters and secondary metabolites in basil plants [21,22,23,24,25,26,27,28], but the effects of specific types of light supplementation on nitrate content in basil, especially short pre-harvest light treatment, have not yet been fully investigated.
The intensity and quality of light reaching the plants during cultivation affect the uptake, translocation, and reduction in nitrates in plant organs [29]. Although nitrogen fertilization is essential to maintain high yields, fertilization with the N-NO3− form can increase nitrate content. In terms of health effects, nitrates are the subject of growing scientific controversy. On the one side, some reports indicate the benefits of eating nitrate-rich vegetables related to reducing the risk of cardiovascular diseases [30]; on the other side, excessive consumption of nitrates, their metabolism to nitrites, and the potential formation of nitrosamines is associated with the increased risk of gastrointestinal cancers [31]. Vegetarian diets, which have become popular in recent times, are rich in vegetables and people following them are more likely to consume nitrates than the average population. A study of the Taiwanese population indicates that exposure to nitrates, thiocyanates, and perchlorates in the diet can adversely affect thyroid function in humans, so it is recommended to control the concentration of these compounds in various food groups, especially vegetables [32].
Green leafy vegetables (especially rocket and spinach) readily accumulate significant amounts of nitrates [33,34]. Among cultivated culinary herbs, basil is reported to accumulate high amounts of nitrates, especially at low light intensities [27,35].
Studies on hydroponically grown purple leaf lettuce indicate that short-term pre-harvest lighting with LEDs has a positive effect on the nutritional value and taste of this vegetable [36]. There are reports that short-term pre-harvest treatment with red light can be used as a technological tool to reduce nitrate content in leafy vegetables [37] and a few studies have examined how pre-harvest lighting (with LEDs) affects the post-harvest quality of vegetables during basil storage [38,39]. According to recent studies, a short-term pre-harvest application of blue or red-blue LEDs may not only be nitrate-reducing, but also beneficial for preserving the nutritional value of sweet basil.
The aim of this study was to determine the effect of assimilation lighting with LED lamps on the yield and quality of Genovese basil, recommended for pot and hydroponic cultivation. The effect of using LED lamps was compared with that obtained using HPS (High Pressure Sodium) lamps, so far the most commonly used for lighting plants in greenhouse cultivation. Particular attention was paid to the nitrate content of basil leaves in relation to different lighting conditions. It was also tested whether short-term treatment with LED light (7 days before harvest) would reduce the content of these compounds in the leaves of plants previously lighted with HPS lamps, or affect other quality characteristics important for the nutritional and health-promoting value of basil.

2. Materials and Methods

2.1. Experimental System and Plant Growing Conditions

The research was conducted at the Greenhouse Experimental Centre of the Warsaw University of Life Sciences, in the cultivation chambers of the Department of Vegetable and Medicinal Plants, in two cycles: I—from 10 October to 21 November 2019 (6 weeks from sowing to harvesting), as well as II—from 29 November 2019 to 10 January 2020 (6 weeks from sowing to harvesting). The results presented here are the average values of the studied parameters for these two cultivation cycles.
Two cultivars of sweet basil (‘Keira’ and ‘Marian’) were included in the study. According to the producer, ‘Keira’ is a Genovese type cultivar with a very fast growth rate, recommended for winter and early spring cultivation. It is suitable for pot production and for fresh markets. Plants have an erect habit and medium-sized leaves, tolerate low temperatures well, and retain a fresh appearance for a long time when brought to the market. ‘Marian’ is a Genovese type standard basil cultivar for pot and hydroponic cultivation. It is characterized by a fast growth rate and a compact habit with densely and evenly distributed leaves with an intense aroma. The cultivar is tolerant to powdery mildew and leaf edge drying, and has high resistance to stress conditions and long transport. An additional advantage of the variety is its high tolerance to thrips [40].
The seeds came from the company Enza Zaden Poland Ltd. (Warsaw, Poland). For sowing, 240 plastic pots (120 for each cultivar) with a diameter of 100 mm and a capacity of 0.4 dm3 were prepared, filled with peat substrate with a pH of 6.5 and the following content of components (mg × dm−3): N—250, P2O5—200, K2O—370, Mg—100, Ca—1000, Fe—10, Cu—12, Mn—3, B—3, Mo—1 and Zn—1). In total, 40 seeds of a given cultivar (‘Keira’ 0.06 g, ‘Marian’ 0.043–0.045 g) were sown into each pot. The pots were stored in a germinator at 25 °C, in the dark, until the seeds germinated. Four days after sowing (DAS), after the seeds germinated, the pots were transferred to the greenhouse, where the temperature was still maintained at 25 °C. After another 10 days, i.e., two weeks after sowing, when the first true leaves were visible, the pots were transferred to the NFT hydroponic system (Figure 1a,b), which consisted of two growing troughs of 7 m length, and 20 pots of basil of both cultivars were placed in each trough. The density was 24 pots per m2.
Plants were grown in three independent NFT systems, under three light combinations: HPS, LED and HPS + 1 week LED. The HPS combination used HPS lamps GAN 6-750 AL SuperAgro, 230 V, 600 W (Gavita International b.v., Rozenburg, The Netherlands). The second combination with LED top lighting used Philips GreenPower LED toplighting module DR/B LB (deep red/blue low blue) 400 V, 195 W (Signify Poland Ltd., Warsaw, Poland). According to the producer the Low Blue (LB) light function in Philips products helps to reduce the emission of harmful short-wavelength blue light, supporting eye health and ensuring comfort during long-term use. In the article, this combination is abbreviated as LED. In the 3rd combination, the plants were first lighted with HPS lamps, as in the HPS combination, and one week before harvest (6th week of cultivation, 35–42 DAS), the lighting was changed to LED DR/B LB lamps, with the same parameters as in the LED combination (Table 1, Figure 1). In the article, this combination is abbreviated as HPS + 1 week LED.
All types of lamps were placed at a distance of 1.20 m from the top edge of the pots. The light intensity for the tested lighting units was monitored using a Radiometer-Photometer RF-100 (Sonopan Ltd., Białystok, Poland) and adjusted to provide 200 ± 20 µmol × m−2 × s−1 PPFD at the top edge of the plant pots. A daily light exposure was 16 h. Light spectra were recorded using an MSC15 handheld spectral light meter (Gigahertz-Optik GmbH, Türkenfeld, Germany). The HPS lamps showed a broad peak at 590 nm, while the LED lamps showed a small peak at 470 nm (blue) and a major peak at 660 nm (red) (Figure 2).
Microclimate conditions and plant fertigation were computer-controlled using the HortiMaX CX500 system and Synopta 1 software (HortiMax B.V., Pijnacker, The Netherlands). During the experiments, the temperature was maintained at ~22 ± 2 °C during the day and 20 ± 2 °C at night, relative humidity averaged 60% and CO2 800 ppm. Plants were supplied with nutrient solution containing the following components (mg × dm3): N-NO3−—230, N-NH4+—10, P—50, K—300, Mg—40, Ca—200, Fe—2, Mn—0.6, B—0.3, Zn—0.3, Cu—0.15, and Mo—0.05. The nutrient solution was prepared from one- or two-component mineral fertilizers designed for hydroponic cultivation. Between 8 a.m. and 1 p.m., the flow of the nutrient solution was turned on every 2 h for 15 min. The initial EC of the nutrient solution was 2.0 mS × cm−1; in the following weeks of cultivation, it was gradually increased to a value of 2.8 mS × cm−1. The parameters of the nutrient solution were controlled every day. The pH value of the nutrient solution was maintained at 6.0. by adding HNO3 (60%, 63.01 g × mol−1; Chempur, Piekary Śląskie, Poland). The amount of nitrogen added with the HNO3 was balanced in the composition of the nutrient solution.

2.2. Plant Growth

For plant growth measurements, 10 pots with the plants of both cultivars from each light combination were randomly selected. Measurements began one week after the pots were inserted into the NFT system (21 DAS). Every week the height of the tallest plant in the pot was measured.

2.3. Yield and Dry Matter Content

To determine the yield, basil plants were cut from 15 randomly selected pots of each cultivar and each light combination 43 DAS. The aboveground part of each plant cut at 2 cm above the surface of the ground, including the stems and leaves, was considered as a herb, then the leaves were separated from the stems and only their weight was determined. The weight of fresh herbs and leaves alone was determined in grams per pot (10 cm2). The dry matter content of the leaves was determined by drying the fresh leaf sample to constant weight at 105 °C.

2.4. Chemical Analyses

Fully expanded fresh leaves of randomly selected plants from each light combination were used for chemical analyses and measurements. All the chemical analyses were performed in three replicates.

2.4.1. Nitrates, Macronutrients, Total Sugars (TS), Total Soluble Solids (TSS) and L-Ascorbic Acid (AA)

For the determination of nitrate content during both harvests, samples were taken at the same time, between 9.30 and 10.00 a.m., 4 h after the lamps were switched on. In total, 10 g of plant sample with activated charcoal (pure p.a., Chempur, Piekary Śląskie, Poland) was shaken in 100 mL of 2% solution of glacial acetic acid (pure p.a., Chempur, Piekary Śląskie, Poland) for 30 min and filtered, and then N-NO3− was determined using a FIAstarTM 5000 Analyzer (FOSS Analytical, Hillerød, Denmark) after reducing nitrate to nitrite by passing the sample solution through a cadmium column. The absorbance of the obtained solution was measured spectrophotometrically at 540 nm.
Based on the same extracts as used for nitrate determination, the content of potassium (K) and calcium (Ca) was determined with the flame photometer M 410 (Sherwood Scientific Ltd., Cambridge, UK) [41]. Phosphorus (P) (in the form of orthophosphate) was determined using the vanadomolybdate spectrophotometric method [42]. The absorbance value in the sample solution was determined at 460 nm and quantified using a series of potassium phosphate monobasic (KH2PO4, ≥99.0%, Sigma-Aldrich Co., St. Louis, MO, USA) solutions (spectrophotometer UV-Vis Shimadzu 1800, Kyoto, Japan).
The content of TS was determined using the Luff-Schoorl method [43].
TSS was determined by the refractometric method using a digital refractometer (Index Instruments Ltd., Bury, UK), reporting the results in °Brix.
The content of AA was determined using the Tillmans’ method [44]. This titration method is based on a reduction in the blue dye 2,6-dichlorophenolindophenol (DCIP) by AA in an acidic medium (2% oxalic acid).

2.4.2. Chlorophylls, Carotenoids, SPAD Index

Samples were homogenized for 30 s with sodium sulfate anhydrous (Na2SO4, pure p.a., Chempur, Piekary Śląskie, Poland) in a 50:1 (w/w) ratio in limited lighting conditions. Afterwards, 5 g of homogenized material was ground with 15 mL of cold (6 °C) acetone (pure p.a., Warchem Ltd., Warsaw, Poland) and quartz sand for 1 min. The extraction was repeated five times. The extracts were filtered into 50 mL graduated flasks and filled with cold acetone, then centrifuged for 10 min at 7000 rpm at 4 °C (Centrifuge 5430R, Eppendorf, Hamburg, Germany). The supernatant was also filtered through a PTFE 25 mm × 0.22 μm syringe filter (Supelco IsoDisc, Supelco Analytical, Bellefonte, PA, USA). Qualitative and quantitative analysis was conducted using the HPLC system with SPD-M20A diode array detector and LCsolution 1.21 SP1 software (Prominence series, Shimadzu, Kyoto, Japan). Separation was achieved with methanol (HPLC grade, Merck, Darmstadt, Germany) isocratic elution using Kinetex C18 2.6 µm, 100 mm × 4.6 mm, 100Å column (Kinetex, Phenomenex, Torrance, CA, USA) at 40 °C. The flow rate was 2 mL × min−1, the injection volume was 5 μL, total time of analysis was 6 min. Compounds were detected at the following wavelengths: 430 nm for chlorophyll a, 445 nm for lutein, 450 nm for β-carotene, and 470 nm for chlorophyll b. The standard stock solutions of carotenoid and chlorophylls standards for HPLC (Merck, Darmstadt, Germany) were prepared by separately dissolving with acetone in a 25 mL volumetric flask. Working standard solutions were made by diluting 10 µL and 100 µL of standard stock solutions with methanol in 10 mL volumetric flasks, 500 µL and 1000 µL in 5 mL volumetric flasks as well as 1000 µL in 2 mL volumetric flasks. The working solutions and undiluted stock solutions were injected into a column in six replicates (n = 6) using an auto-sampler. Six-point calibration curves were plotted according to the external standard method by correlating concentration with peak area. Standard curve parameters were calculated with MS Excel 2013 (Microsoft, Redmond, WA, USA). The signal-to-noise ratio approach was used to determine LOD (S/N of 3:1) and LOQ (S/N of 10:1). The peak table and spectra library (190–800 nm) of individual compounds were created (Table 2).
Leaf chlorophyll content (expressed as SPAD index) was estimated with the portable equipment SPAD-502 (Minolta, Tokyo, Japan). For each cultivar and light combination, 10 pots were randomly selected for the measurements. The measurements were made on three plants from each pot, on the third leaf from the shoot apex. They were carried out once for each experimental cycle (19 November 2019 and 13 January 2020), between 9 and 11 a.m.

2.5. Statistical Analysis

The results were statistically processed using Statgraphics Centurion XVII 2016 software (Statgraphics Technologies, Inc., The Plains, VA, USA). One-way analysis of variance (ANOVA) was performed, and mean values were compared using Tukey’s HSD test at a significance level of α = 0.05.

3. Results

3.1. Plant Growth

Plant height differed significantly depending on the light conditions. After the first week of lighting with HPS and LED lamps (3rd week of cultivation) basil grown under LED light was lower than that grown under HPS light, irrespective of cultivar. In the following two weeks (4th and 5th), the studied cultivars differed in their response to lighting source. The plant height of the ‘Keira’ cultivar was greater under HPS than under LED light, while this trend was not noticeable in the ‘Marian’ cultivar (Figure 3). In the last week of the experiment, plants of the ‘Keira’ cultivar grew faster in combination with LED light only, reaching a similar height as the plants grown under HPS light and surpassing those transferred from HPS to LED lighting conditions (HPS + 1 week LED) (Figure 3a). In the basil of the ‘Marian’ cultivar, there were no such significant differences in plant height depending on the lighting method. However, in the last week of observation, plants grown under LED light throughout the experiment were higher than those transferred to LED lighting for the last week (Figure 3b). The average height of ‘Keira’ plants at harvest was 22.1 cm, while ‘Marian’ plants had an average height of 19.3 cm.

3.2. Yield and Dry Matter Content

The yield of basil whole herb and of the leaves alone was different according to the lighting type. The average herb weight of ‘Keira’ plants was 49.69 g per pot, while ‘Marian’ plants had an average weight of 36.26 g per pot, of which approximately 60% was leaf weight. In the case of both investigated basil cultivars, the yield of fresh herb from plants under LED lighting was higher than in the basil transferred to LED lighting conditions for the last week before harvest. In ‘Keira’ cultivar, a high yield was also obtained with HPS lighting. The herb yield of the ‘Keira’ cultivar in LED combination averaged 53.8 g per pot, while in the ‘Marian’ cultivar, the herb weight per pot was 40.9 (Figure 4a,b).
The dry matter content of basil leaves varied according to the type of lighting used. In both tested cultivars, significantly higher dry matter content was found in the leaves of plants lighted with LED lamps compared to both plants lighted with HPS lamps and those treated with LED light in the last week of cultivation (Table 3).

3.3. Chemical Analyses

3.3.1. Nitrates

In the case of both investigated basil cultivars, plants growing under HPS lighting were characterized by the highest nitrate content. Lighting the plants with LED lamps only (LED combination) resulted in significantly lower NO3− accumulation in the leaves compared to plants lighted with HPS lamps (Figure 3a,b). The average nitrate content of basil of the ’Keira’ cultivar was 2640 mg × kg−1 FW, while that of the ‘Marian’ cultivar was 3128 mg × kg−1 FW.
In plants of the ‘Keira’ cultivar grown under LED lights only, the nitrate content averaged 2189 mg × kg−1 FW, which was 35.6% lower than under HPS light, while in the ‘Marian’ cultivar it was 2558.9 mg × kg−1 FW, which was 26.7% lower than in the HPS combination. The application of LED lighting for 7 days before harvest also reduced the content of these compounds in the leaves compared to HPS lighting, with the effect being stronger for ‘Keira’ (23.5% reduction), while ‘Marian’ showed a decrease in only 4.4% (Figure 5a,b).

3.3.2. K, P, Ca, TS, TSS and AA

Leaves of basil grown under different types of lighting did not differ significantly in the content of K, P, and Ca. In the case of both cultivars, plants lighted with LED lamps throughout the experiment were characterized by a higher content of TS than those grown under HPS lighting or HPS lighting followed by LED lighting (for the last 7 days before harvest). In ‘Keira’ cultivar similar relationship was observed for TSS. In the ‘Marian’ cultivar both long-term and short-term LED light treatment caused the increase in TSS content. Both varieties grown under LED light had significantly higher AA content compared to plants from the other combinations and the leaves of the cultivar ‘Marian’ were slightly richer in this compound. Leaves of basil ‘Keira’ were characterized by higher K content (mg × 100 g−1 FW), while leaves of cultivar ‘Marian’ were richer in P and Ca (Table 4 and Table 5).

3.3.3. Chlorophylls and Carotenoids

The lighting of basil with different types of lamps affected the content of chlorophyll a, chlorophyll b, and carotenoids (β-carotene and lutein). The leaves of basil grown under LED light showed significantly higher contents of chlorophyll a and β-carotene, while the contents of chlorophyll b and lutein were similar in the leaves of plants grown under all light combinations. There were no clear differences in chlorophyll and carotenoid contents between plants of the tested varieties (Table 6 and Table 7).
In both cultivars, a significantly higher SPAD index value was found in the leaves of plants lighted with LED lamps throughout the cultivation period compared to basil grown under HPS lamps. In the ‘Keira’ cultivar, application of LED light only in the last week before harvest did not cause the increase in this parameter compared to the values obtained in the leaves of plants lighted with HPS lamps, but basil leaves of the ‘Marian’ cultivar had a slightly higher SPAD index in this combination (Figure 6a,b).

4. Discussion

Light is primarily the driving force of photosynthesis, but it is also crucial for regulating nitrate uptake, translocation, and assimilation into organic compounds [29]. Both light intensity, day length, and light quality affect the plant’s metabolism. Yang et al. [45] report that red and blue light influenced the accumulation and composition of carbohydrates, which determine both the taste and quality of vegetables. Optimization of these parameters in the cultivation results in a high-quality product desired by the consumer. Obtaining a reduction in nitrate accumulation and, at the same time, increasing the number of compounds responsible for the taste of leafy vegetables and, in basil and aromatic plants, for the aroma, is possible through an appropriate choice of light quality [46].

4.1. Basil Growth, Yield, and Dry Mass Content Under Different Types of Lighting

LEDs, due to their ability to provide light of different spectra, are becoming increasingly important in horticultural crops. In the light spectrum, red and blue areas are often considered the main energy sources of plants for photosynthetic CO2 assimilation [47]. Plant temperature is also an important factor in primary metabolism and diurnal rhythm. LEDs are known to produce significantly less thermal radiation than HPS lamps [48]. Because LEDs emit much of their heat through convection rather than radiative cooling, they result in slightly cooler leaf temperatures. The leaf temperature of plants grown under HPS lighting is typically two to three degrees Celsius higher than under LED lighting, which can be useful in the cold winter months, increasing the rate of photosynthesis compared to plants without this additional heat. Increased leaf temperature from infrared wavelengths directly increases leaf temperature, as well as metabolic activity and transpiration [49]. According to Dorr et al. [50], basil plant morphology is most affected by red to far red ratio (R:FR) and leaf temperature. In turn, as reported by Jeong et al. [51], FR light and temperature interactively regulate plant growth and morphology: as the percentage of FR light and temperature increases, the leaf length and height of basil plants increase, but the stimulating effect of FR light on elongation is greater at lower temperatures (20/20 °C).
Under the conditions of this experiment (22/20 °C), in Genovese type cultivars tested, the most intensive growth took place at the end of the 5th and 6th week of cultivation, regardless of the way the plants were lighted. The temperature factor may have had an impact on the growth of ‘Keira’ plants, as in the initial weeks of cultivation the plants grew more intensively under HPS light. According to Larsen et al. [8], some responses to PPFD and spectra are cultivar-dependent. The increase in plant height during the last week of growth was slightly higher in plants grown continuously at the same type of supplemental lighting (either HPS or LED) than in those transferred from HPS to LED lighting, which could indicate a stress response to the change in light conditions in the latter group.
It is also possible to notice slight differences in the reaction of the tested cultivars to the applied lighting. Only for basil ‘Marian’ significantly the highest weight, both of the herb and of the leaves themselves, was obtained under LED light. Earlier studies [19,52] indicate that the use of blue and far-red light improves basil mass accumulation. Both tested varieties showed a significantly higher dry mass content in leaves at LED lighting than in the combination with HPS lamps.

4.2. Effect of Lighting Type on Nitrate Content

Nitrogen is considered the most yield-forming of all macronutrients, which is particularly beneficial for plant growth and yield, but the danger of using large amounts of nitrate nitrogen is the possibility of excessive nitrate accumulation in crops, which is harmful to human health. Among the dietary components tested, the highest nitrate content was found in arugula, lettuce and spinach [53,54]. The average nitrate content of basil of the ‘Keira’ cultivar was 2640 mg × kg−1 FW, while that of the ‘Marian’ cultivar was 3128 mg × kg−1 FW. As is known, the genotypic effect is recognized as the principal determinant of quantitative and qualitative variation in nutrient contents in vegetables [55].
The application of LED lighting in this experiment resulted in a reduction in nitrate content with both, exclusive and short-term LED lighting. With only LED lighting, NO3− content turned out to be nearly 30% lower compared to plants grown under HPS light only. This is confirmed by a study by Ohashi-Kaneko et al. [56], in which blue and blue-red light lighting reduced nitrate content in leaf lettuce compared to white light, and in turn, red light lighting reduced nitrate content in spinach. Using LED with a deep red light in this experiment probably affected the activity of the enzyme nitrate reductase. A study by Viršilė et al. [57] indicates that both spectral differences and light intensity have significant, species-specific effects on nitrate content and reducing enzyme activity. At low light levels, red light is able to reduce nitrate concentration in leaves by increasing nitrate reductase activity [54]. Red light is involved in regulating reductase activity because the expression of this enzyme is promoted by light absorbed by phytochrome [29]. Therefore, higher reductase activity may be associated with the red spectrum.
After pre-harvest LED treatment, the decrease in nitrates content was noticeable, although the response was different in the two Genovese basil cultivars tested. Such treatment reduced the content of these compounds in the leaves compared to HPS lighting, with the effect being stronger for ‘Keira’ (23.5% reduction) than for ‘Marian’ (4.4% reduction), which may be related to cultivars characteristics.

4.3. Effect of Lighting Type on Macronutrients, TS, TSS and AA Content

The type of plant lighting did not affect the content of macronutrients in basil leaves. Research by Pennisi et al. [24] indicates that the use of LED red/blue (R/B) lighting in a 3:1 ratio results in a greater accumulation of N, P, K, Ca, Mg, and Fe in the plants. Other studies show that the way basil plants are lighted can affect Ca, K, and P levels [19]. In the present study, no such relationship was reported.
There were significantly higher contents of TS, TSS, and AA in basil grown only under LED lighting compared to HPS lamps, while there was no increase in the content of the compounds after LED light treatment at the end of cultivation, excepting the content of TSS in basil ‘Marian’. A similar increase in °Brix values in only one of the tested cultivars was observed in another study [23]. There are also reports that the higher TS contents along with the stronger sucrose synthesizing enzyme activity were detected in lettuce plants treated with R/B LED light [58], which can suggest higher sugar content in plants treated with LED light. In the present experiment, an increase in TS was found in both basil cultivars only with LED lighting throughout the growing period.
The AA content in fruits and vegetables increases with light intensity [59,60]. Blue and blue-red light treatment may be most beneficial in this regard, according to Ohashi-Kaneko et al. [56]. In the present study, AA content was higher in the leaves of both cultivars grown under LED lighting—‘Keira’ 16.6 mg × 100 g−1 FW, ‘Marian’ 16.1 mg × 100 g−1 FW, which was probably the result of a higher proportion of blue light in LED than in HPS lamps.

4.4. Effect of Lighting Type on Chlorophylls and β-Carotene Content

In order for plants to begin photosynthesis, they must capture photons of light with the help of photosynthetic pigments present in the plant, including chlorophyll a and b or β-carotene, which use light most effectively in the red and blue wavelength ranges. It has already been reported that both red light and blue light increase the synthesis of carotenoids [61]. In our study, a significantly higher content of chlorophyll a and β-carotene, as well as the SPAD index value, was recorded in the leaves of plants grown under LED lighting alone. This may suggest that, as in the case of AA, the presence of blue light in LEDs increased chlorophyll a and β-carotene content. According to Lobiuc et al. [25], the use of blue light in cultivation can result in an increase in chlorophyll concentration in the plant. This is confirmed by an experiment conducted by Carvalho et al. [26], who found that plants lighted with blue light grew better and had higher chlorophyll content, and studies on lettuce indicate that short-term lighting with LEDs before harvest improved carotenoid levels. Therefore, one would expect an increase in the content of these components in the HPS + 1 week LED combination as well, but no such effect was found in the present experiment. Values obtained in research on basil microgreens indicate that HPS lamps supplemented by LED red light significantly induced the accumulation of β-carotene (47.9%) in basil [62]. The same authors state that such lighting stimulates lutein content (48.8%), but no significant differences in chlorophyll b and lutein content were found in the present experiment, depending on the lighting type.

5. Conclusions

The principles of sustainability, the need to reduce the carbon footprint, and the efficient use of resources are encouraging producers to use new techniques with low water consumption and energy-efficient LED light sources. The latter easily allows modification of the spectral distribution and light intensity, resulting in the expected plant response. The results of the present study indicate that light quality control is useful for nitrate reduction, as well as for increasing the yield and nutritional value of basil, with great potential for use in hydroponic basil production.
LED DR/B LB lighting, with a higher proportion of blue light than HPS, significantly affected the nitrate content of basil leaves, with the greatest reduction in these compounds found in the combination lighted throughout the experiment with LED light, nearly 30% lower compared to plants grown under HPS light alone. One week of lighting with LED lamps at the end of cultivation also resulted in a reduction in nitrate content, but less than with LED-only lighting, and perhaps the effect would be stronger with shorter continuous lighting. Furthermore, this response appeared to differ between the two Genovese basil cultivars tested, which may be related to varietal characteristics and requires further research.
LED lighting also had a positive effect on leaf yield and chemical composition of basil. LED-only lighted plants had higher contents of TS, TSS, AA, chlorophyll a, and β-carotene than basil grown under HPS lights only, but 7 days of supplementation did not significantly change the content of these compounds in the plants. Further research on pre-harvest light treatment of basil is recommended to improve both yield and quality.

Author Contributions

Conceptualization, M.M. and K.K.; methodology, M.M., J.L.P. and K.K.; software, J.L.P.; validation, M.N. and J.L.P.; formal analysis, M.N., M.M., A.G. and J.L.P.; investigation, M.M., J.L.P., A.G., M.S.-R., J.G.-W. and K.K.; resources, J.G.-W.; data curation, M.M.; writing—original draft preparation, M.M.; writing—review and editing, A.G., K.K., M.S.-R. and J.G.-W.; visualization, M.M. and K.K.; supervision, K.K. and J.G.-W.; project administration, J.G.-W.; funding acquisition, K.K. and J.G.-W. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

All the data that support the findings of this study are included in the paper. The raw data will be made available on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Plants grown under HPS (a) and LED (b) supplemental lighting.
Figure 1. Plants grown under HPS (a) and LED (b) supplemental lighting.
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Figure 2. Light spectra of the applied HPS (a) and LED (b) lamps. It was measured in the presence of daylight. The average total daily solar radiation during the study period was 268 J × cm−2.
Figure 2. Light spectra of the applied HPS (a) and LED (b) lamps. It was measured in the presence of daylight. The average total daily solar radiation during the study period was 268 J × cm−2.
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Figure 3. Plant height depending on lighting type: (a) ‘Keira’ basil, (b) ‘Marian’ basil (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type on each measurement week (Tukey’s test, α = 0.05). ns = not significant.
Figure 3. Plant height depending on lighting type: (a) ‘Keira’ basil, (b) ‘Marian’ basil (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type on each measurement week (Tukey’s test, α = 0.05). ns = not significant.
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Figure 4. Yield of fresh herb (H) and leaves alone (L) of basil cultivar ‘Keira’ (a) and ’Marian’ (b), depending on lighting type (average of two crop cycles). Different lowercase letters indicate significant differences in herb yield resulting from lighting type; different capital letters indicate significant differences in the leaf yield (Tukey’s HSD test, α = 0.05).
Figure 4. Yield of fresh herb (H) and leaves alone (L) of basil cultivar ‘Keira’ (a) and ’Marian’ (b), depending on lighting type (average of two crop cycles). Different lowercase letters indicate significant differences in herb yield resulting from lighting type; different capital letters indicate significant differences in the leaf yield (Tukey’s HSD test, α = 0.05).
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Figure 5. Concentration of NO3− in leaves: (a) ‘Keira’ basil; (b) ‘Marian’ basil (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s HSD test, α = 0.05).
Figure 5. Concentration of NO3− in leaves: (a) ‘Keira’ basil; (b) ‘Marian’ basil (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s HSD test, α = 0.05).
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Figure 6. SPAD index in basil leaves: (a) ‘Keira’ basil; (b) ‘Marian’ basil (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type on each measurement week (Tukey’s HSD test, α = 0.05).
Figure 6. SPAD index in basil leaves: (a) ‘Keira’ basil; (b) ‘Marian’ basil (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type on each measurement week (Tukey’s HSD test, α = 0.05).
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Table 1. Lighting period and type during the basil production cycle.
Table 1. Lighting period and type during the basil production cycle.
Lighting TypeLighting Period (Week After Sowing)
3456
HPS
LED
HPS + 1 week LED
Table 2. Validation parameters of the HPLC-DAD analysis (n = 6).
Table 2. Validation parameters of the HPLC-DAD analysis (n = 6).
LOQ
(µg × L−1)		LOD
(µg × L−1)		Linear Range
(µg × mL−1)		R
(r2)		Calibration EquationPrecision Inter-Day (CV)Precision Intra-Day (CV)tRCompound
1.860.560.41–408.600.999y = 10553.4x + 324.50.870.490.76Lutein
0.500.150.38–338.800.999y = 5245.2x + 654.30.890.501.29Chlorophyll b
3.160.940.39–387.600.999y = 3143.4x + 432.20.780.461.82Chlorophyll a
3.260.970.38–383.800.999y = 4324.2x − 324.50.670.323.77β-carotene
Table 3. Dry matter content (%) in leaves of ‘Keira’ and ‘Marian’ cultivars depending on lighting type (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s HSD test, α = 0.05).
Table 3. Dry matter content (%) in leaves of ‘Keira’ and ‘Marian’ cultivars depending on lighting type (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s HSD test, α = 0.05).
Lighting Type‘Keira’‘Marian’
HPS8.58 ± 0.36 b8.34 ± 0.59 b
LED9.33 ± 0.41 a8.84 ± 0.38 a
HPS + 1 week LED8.67 ± 0.38 ab8.74 ± 0.40 ab
Table 4. Concentration of the selected nutrients in fresh leaves of ‘Keira’ basil (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s test, α = 0.05); ns—not significant.
Table 4. Concentration of the selected nutrients in fresh leaves of ‘Keira’ basil (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s test, α = 0.05); ns—not significant.
‘KEIRA’
Lighting TypeK
(mg × 100 g−1 FW)		P
(mg × 100 g−1 FW)		Ca
(mg × 100 g−1 FW)		TS
(g × 100 g−1 FW)		TSS
(°Brix)		AA
(mg × 100 g−1 FW)
HPS453.8 ± 9.5 ns38.32 ± 2.9 ns39.58 ± 4.4 ns 0.50 ± 0.10 b3.57 ± 0.18 b14.2 ± 2.4 b
LED454.7 ± 5.0 ns 39.47 ± 0.5 ns39.19 ± 2.1 ns0.58 ± 0.09 a4.55 ± 0.05 a16.6 ± 1.1 a
HPS + LED451.3 ± 7.8 ns 39.22 ± 1.2 ns40.84 ± 1.0 ns0.49 ± 0.07 b3.22 ± 0.08 b14.9 ± 3.2 b
Table 5. Concentration of the selected nutrients in fresh leaves of ‘Marian’ basil (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s test, α = 0.05); ns—not significant.
Table 5. Concentration of the selected nutrients in fresh leaves of ‘Marian’ basil (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s test, α = 0.05); ns—not significant.
‘MARIAN’
Lighting TypeK
(mg × 100 g−1 FW)		P
(mg × 100 g−1 FW)		Ca
(mg × 100 g−1 FW)		TS
(g × 100 g−1 FW)		TSS
(°Brix)		AA
(mg × 100 g−1 FW)
HPS406.9 ± 12.0 ns 44.84 ± 2.2 ns63.85 ± 3.5 ns0.43 ± 0.02 b3.32 ± 0.10 b12.5 ± 0.50 b
LED394.2 ± 10.5 ns 45.58 ± 0.6 ns 63.80 ± 7.2 ns0.50 ± 0.05 a3.90 ± 0.00 a16.1 ± 0.25 a
HPS + LED411.4 ± 13.0 ns 45.08 ± 2.9 ns63.94 ± 3.5 ns 0.46 ± 0.00 b4.03 ± 0.15 a13.2 ± 3.33 b
Table 6. Chlorophylls and carotenoids content in ‘Keira’ fresh leaves (mg × 100 g−1 FW) (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s test, α = 0.05); ns—not significant.
Table 6. Chlorophylls and carotenoids content in ‘Keira’ fresh leaves (mg × 100 g−1 FW) (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s test, α = 0.05); ns—not significant.
‘KEIRA’
Lighting TypeChlorophyll aChlorophyll bLuteinβ-Carotene
HPS107.51 ± 0.94 b29.92 ± 0.33 ns 10.17 ± 0.09 ns 16.51 ± 0.26 b
LED119.25 ± 2.87 a31.37 ± 0.60 ns10.69 ± 0.12 ns 17.76 ± 0.38 a
HPS + LED107.60 ± 1.75 b29.25 ± 0.47 ns 9.96 ± 0.35 ns 16.44 ± 0.38 b
Table 7. Chlorophylls and carotenoids content in ‘Marian’ fresh leaves (mg × 100 g−1 FW) (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s test, α = 0.05); ns—not significant.
Table 7. Chlorophylls and carotenoids content in ‘Marian’ fresh leaves (mg × 100 g−1 FW) (average of two crop cycles). Different lowercase letters indicate significant differences resulting from lighting type (Tukey’s test, α = 0.05); ns—not significant.
‘MARIAN’
Lighting TypeChlorophyll aChlorophyll bLuteinβ-Carotene
HPS108.99 ± 3.53 b30.00 ± 1.01 ns10.07 ± 0.15 ns16.64 ± 0.19 b
LED112.55 ± 3.25 a30.36 ± 0.37 ns 10.18 ± 0.06 ns 17.90 ± 0.52 a
HPS + LED110.74 ± 3.70 b29.76 ± 1.05 ns10.19 ± 0.19 ns 16.79 ± 0.12 b
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Mirgos, M.; Geszprych, A.; Przybył, J.L.; Niedzińska, M.; Sujkowska-Rybkowska, M.; Gajc-Wolska, J.; Kowalczyk, K. Effect of Lighting Type on the Nitrates Concentration, Selective Bioactive Compounds and Yield of Sweet Basil (Ocimum basilicum L.) in Hydroponic Production. Agronomy 2025, 15, 966. https://doi.org/10.3390/agronomy15040966

AMA Style

Mirgos M, Geszprych A, Przybył JL, Niedzińska M, Sujkowska-Rybkowska M, Gajc-Wolska J, Kowalczyk K. Effect of Lighting Type on the Nitrates Concentration, Selective Bioactive Compounds and Yield of Sweet Basil (Ocimum basilicum L.) in Hydroponic Production. Agronomy. 2025; 15(4):966. https://doi.org/10.3390/agronomy15040966

Chicago/Turabian Style

Mirgos, Małgorzata, Anna Geszprych, Jarosław L. Przybył, Monika Niedzińska, Marzena Sujkowska-Rybkowska, Janina Gajc-Wolska, and Katarzyna Kowalczyk. 2025. "Effect of Lighting Type on the Nitrates Concentration, Selective Bioactive Compounds and Yield of Sweet Basil (Ocimum basilicum L.) in Hydroponic Production" Agronomy 15, no. 4: 966. https://doi.org/10.3390/agronomy15040966

APA Style

Mirgos, M., Geszprych, A., Przybył, J. L., Niedzińska, M., Sujkowska-Rybkowska, M., Gajc-Wolska, J., & Kowalczyk, K. (2025). Effect of Lighting Type on the Nitrates Concentration, Selective Bioactive Compounds and Yield of Sweet Basil (Ocimum basilicum L.) in Hydroponic Production. Agronomy, 15(4), 966. https://doi.org/10.3390/agronomy15040966

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