To elucidate how roots respond to hydroponics, we investigated the mechanisms by which nutrient solution flow influences root growth in hydroponic lettuce via phenotypic analysis combined with single-cell RNA sequencing. Nutrient solution flow exerted a dual-phase effect on lettuce root growth, characterized by initial inhibition followed by subsequent promotion. Although initially, root biomass and morphological indices were significantly lower under flow treatment than under static treatment, this trend rapidly reversed by days 2 and 3 and all the measured indices showed improved root growth under flow treatment. Single-cell transcriptomic analysis enabled the construction of a comprehensive cellular atlas of hydroponic lettuce roots, which indicated heterogeneous transcriptional responses for lettuce roots under static and flow treatments. Flow treatment altered root cell composition, inducing decreases in initial cells and increases in vascular cells. Pseudotime trajectory analysis suggested that the differentiation of initial cells into vascular tissues was associated with plant hormone signaling and MAPK pathway-related gene expression, and also revealed differential expression of key functional genes, including ACO3 in root cap cells and CAM7 in xylem cells. Therefore, this study provides insights into the transcriptional regulatory framework of hydroponic lettuce roots in response to nutrient solution flow, which may provide a basis for optimizing hydroponic crop production via rhizosphere environment regulation.

ABSTRACT Plant factories are an innovative agricultural model that leverage controlled environments and advanced regulation technologies to improve land‐use efficiency and reduce resource dependence. However, their development is constrained by high energy consumption. Given the high costs and environmental impacts associated with fossil‐fuel‐based electricity, renewable energy sources such as solar power have emerged as promising alternatives. In this study, a model vertical plant factory consisting of 20 stories (area = 100 m2) was applied to 21 Chinese cities with populations exceeding 5 million. Three power supply modes were considered: a grid‐powered system, a standalone solar‐powered system, and a grid‐solar hybrid system. The net present cost (NPC), levelized cost of energy (COE), and carbon dioxide emissions were assessed for each mode. Among the three systems, the hybrid system substantially reduced economic costs (40.87%–65.68% lower NPC than the grid‐powered system), whereas the standalone solar‐powered system most effectively reduced carbon dioxide emissions (85.99%–97.93% lower than the grid‐powered system). By comprehensively analysing solar resources, system design, economic indicators, and emission reduction benefits, this study provides scientific evidence to support decision‐making and implementation of vertical agriculture farming projects, promoting the coordinated advancement of agriculture and environmental protection.

Soilless culture enables precise control of root-zone environments, offering solutions to land scarcity and food security. Plant roots exhibit high phenotypic plasticity, yet no recent review has systematically synthesized how biotic and abiotic factors jointly shape root morphology and physiology specifically under soilless conditions. This review synthesizes literature from the past two decades, focusing on studies that examine root responses in hydroponic, aeroponic, and substrate-based soilless systems. We organize the evidence into three parts: (1) biotic factors (plant growth-promoting rhizobacteria, arbuscular mycorrhizal fungi, and pathogens); (2) abiotic factors (light intensity/spectrum, temperature, rhizosphere oxygen, and nutrient solution properties including concentration, composition, pH, and flow rate); and (3) interactive effects between these factors. Our analysis reveals three main insights. First, in soilless systems, the simplified microbial environment amplifies both the beneficial effects of PGPR/AMF (via phytohormone modulation and antioxidant activation) and the virulence of pathogens, compared to soil conditions. Second, among abiotic factors, light quality and nutrient solution flow have emerged as particularly potent regulators—blue/red light differentially control auxin transport, while flow-induced mechanical force alters lignin deposition and hormone signaling in ways not observed in static soil. Third, emerging evidence indicates that biotic–abiotic interactions (e.g., microbes × pH, light × temperature, oxygen × nutrient composition) produce non-additive effects on root architecture that single-factor studies cannot predict. We identify five critical gaps: insufficient multi-factor coupling studies, limited molecular understanding of root response networks under combined stresses, lack of crop-specific regulation models, a triple bottleneck in PGPR strain–environment–host adaptation, and high energy/material costs of soilless systems. Future priorities should integrate multi-omics with AI-driven environmental control and CRISPR-based root trait engineering. This review provides a framework for understanding root-environment interactions in soilless culture and outlines a research base for precision root-zone management.

To optimize hydroponic management and ensure healthy root development, it is important to understand how nutrient solution flow affects root development during the seedling stage. However, the molecular cascades underlying root system establishment remain unclear. Using hydroponic lettuce as a model, this study examines how nutrient solution flow, as a hydromechanical stimulus, dynamically influences the processes and molecular mechanisms that regulate root morphology. The root system revealed a two-phase adaptation strategy: an initial phase (day 1) characterized by growth inhibition, followed by a second phase (day2-day6), showing substantial improvements in biomass and morphological indicators, including root length and surface area, demonstrating strong plasticity. Integrated multi-omics analysis (transcriptomics, proteomics, phosphoproteomics, and phytohormone metabolomics) revealed a complex regulatory network from signal perception to physiological responses. Receptor-like kinases, including Brassinosteroid insensitive 1-associated receptor kinase 1 (BAK1) and the phytosulfokine receptor, serve as potential mechanosensors, triggering downstream intracellular signaling. This signaling network reprograms the balance of core phytohormones, including the synergistic upregulation of auxin and jasmonic acid, deregulated ethylene signaling, and attenuated abscisic acid signaling, promoting adaptive root growth. The phenylpropanoid pathway exhibited distinct reprogramming: upstream synthases were generally downregulated, whereas downstream peroxidases were markedly induced, indicating rapid cell wall reinforcement through enhanced lignin monomer polymerization rather than de novo synthesis. Protein-protein interaction analysis further revealed several hub proteins, such as CYP450 and cinnamyl-alcohol dehydrogenase, which may integrate multi-signal regulation. Overall, this study advances the understanding of plant mechanoperception and response mechanisms and provides a molecular basis and potential targets for optimizing root architecture in smart hydroponic systems.

Tomatoes, as a globally cultivated staple crop, face salinity stress-a critical challenge that severely impacts plant growth and fruit quality. Peroxidase (POD) is a powerful enzyme found in plants. It is related to respiration, photosynthesis and oxidation of growth factors. As an important marker of plant stress resistance, its activity level is closely related to stress resistance ability, so it has become a key indicator to evaluate the health status of tomato plants. Traditional methods for detecting leaf cell POD activity have limitations, previous research methods are mostly limited to the determination of the overall POD activity in cells, or only can roughly locate the general region of POD in cells, and there is a significant lack of understanding of the fine distribution pattern of POD in cells and the difference of activity in different cell regions. This study aims to use the prediction model based on micro hyperspectral imaging technology (MHSI) to rapidly identify the POD function of tomato plants, and reveal the distribution pattern of POD activity in leaves and cells through visualization. Methods: Hyperspectral information of 324 tomato leaves for different growth and development periods was used. For extracting characteristic wavelengths, successive projection algorithm (SPA), interval random frog jump (IRF), genetic partial least squares algorithm (GAPLS), competitive adaptive reweighted sampling (CARS), and interval variable iterative space contraction (iVISSA) were applied. To develop the POD activity prediction model, Partial Least Squares Regression (PLSR), BP Neural Networks (BPNN), Radial Basis Function Neural Networks (RBFNN), Least Squares Support Vector Machines (LSSVM) and Convolutional Neural Networks (CNN) models were applied. Based on the developed prediction model in leaves, the POD activity and its distribution in cell level could be determined. Results: The results showed that the baseline calibration (Baseline) preprocessing method was selected for preprocessing the raw spectral data.The CARS method was the best for modelling the characteristic wavelengths obtained (Correlation Coefficient of Calibration Set, Rc = 0.856, Correlation Coefficient of Prediction Set, Rp = 0.794). The best performance of POD activity prediction model was constructed based on CARS-CNN (Rc = 0.894, Rp = 0.801),The distribution of POD activity in the cell was also well visualized. Conclusions: An innovative method for rapid detection of POD activity of tomato under salt stress was developed and related technical references with visualization of the distribution of POD activity in leaves and cells.

Nutrient solution flow is important for the growth and root morphology of lettuce in hydroponics, requiring precise regulation to optimise yield and quality. However, the mechanisms involved remain poorly understood. We examined the influence of varying nutrient solution flow rates on lettuce growth, root morphology, and nitrogen uptake. We assessed lettuce performance at five growth stages, measuring shoot and root dry and fresh weights, root morphology, and nitrogen uptake. Particle image velocimetry was employed to visualise the flow field, providing a deeper understanding of how flow patterns impact the root environment. In the early growth stage, lettuce under no flow conditions exhibited higher shoot and root biomass. However, moderate flow consistently outperformed other conditions as growth progressed, demonstrating significantly higher fresh and dry weights. High flow initially suppressed growth, highlighting the detrimental effects of excessively fast flow rates. No flow initially promoted root development, while moderate flow enhanced root growth later in the lifecycle. Nitrogen uptake analysis showed that moderate flow achieved the highest efficiency, while high flow increased nitrogen uptake flux in later stages. PIV visualisation revealed that moderate flow delivered uniform flow vectors and moderate velocity, enhancing nutrient ion contact with roots and uptake efficiency. In contrast, high flow resulted in chaotic flow vectors, high vorticity, and potential root damage, reducing uptake efficiency. Under no flow conditions, nutrient ion transport relied solely on diffusion, limiting nutrient availability during rapid growth and maturation. In conclusion, moderate flow was optimal for promoting lettuce growth and root development.

The application of spectral-shifting films in greenhouses to shift green light to red light has shown variable growth responses across crop species. However, the yield enhancement of crops under altered light quality is related to the collective effects of the specific biophysical characteristics of each species. Considering only one attribute of a crop has limitations in understanding the relationship between sunlight quality adjustments and crop growth performance. Therefore, this study aims to comprehensively link multiple plant phenotypic traits and daily light integral considering the physiological responses of crops to their growth outcomes under SF using artificial intelligence. Between 2021 and 2024, various leafy, fruiting, and root crops were grown in greenhouses covered with either PEF or SF, and leaf reflectance, leaf mass per area, chlorophyll content, daily light integral, and light saturation point were measured from the plants cultivated in each condition. 210 data points were collected, but there was insufficient data to train deep learning models, so a variational autoencoder was used for data augmentation. Most crop yields showed an average increase of 22.5

Traditional soil cultivation of lettuce faces challenges; hydroponic technology offers solutions to improve lettuce production. However, the interrelationships among the root phenotype of lettuce, auxin synthesis and signal transduction, and nutrient solution flow, and their effects on hydroponic lettuce growth remain unclear. We investigated the effects of nutrient solution flow state on lettuce’s early growth, transcriptomic changes, and auxin-related gene expression. Growth indicators were measured 2, 4, and 6 days after transplanting. The shoot and root fresh weights, total root length, and root surface area were significantly higher under the flow treatment than under the non-flow condition. The shoot fresh weight increased by 29, 64, and 31%, respectively, at the three growth stages. A clear distinction was observed between the samples from different treatment groups. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways that were commonly enriched included “Plant hormone signal transduction (auxin)”. Moreover, the significantly enriched Gene Ontology (GO) terms varied across different time points, which vividly reflected the dynamic characteristics of the plant’s response. Genes related to auxin biosynthesis—such as AL3F1, YUC5, and AMI4G—exhibited higher expression levels under the flow treatment. Overall, these results indicate that nutrient solution flow can promote auxin synthesis and signal transduction in early roots of lettuce.

The mechanisms underlying plant root response to mechanical environmental stimuli are crucial for plant growth, development, and environmental adaptation. In this review, we examine the mechanical environments encountered by plant roots, including the different types of mechanical stimuli they experience. We describe in detail the mechanisms that enable roots to perceive these stimuli and their modes of action. Unfavorable mechanical stimuli can cause roots to alter their growth patterns and rates. Morphologically, roots become thicker, enhancing their stress resistance. Mechanical stimuli influence the activity of hormones, including auxin and ethylene, which jointly regulate root growth. Auxin promotes cell elongation in roots, whereas ethylene can inhibit root growth under certain conditions. Plants modulate antioxidant enzyme activity and osmoregulatory substance accumulation to cope with environmental stress. We explored the molecular regulatory mechanisms underlying plant root adaptation to mechanical stimuli, including those involved in regulating genes and signal transduction pathways. Finally, we suggest future research directions, including an in-depth study of the multi-signal integration mechanism of roots and gene editing technology for improving plant adaptability. This review provides a basis for studying the interactions between plants and mechanical environments for plant adaptation and agricultural production.

Soilless cultivation technology is a key means of overcoming traditional agricultural resource limits, providing an important path to efficient and sustainable modern agriculture by precisely regulating crop rhizospheric environments. This paper systematically reviews the technical system of soilless cultivation, nutrient solution management strategies, the interaction mechanism of rhizosphere microorganisms, and future development directions, aiming to reveal its technical advantages and innovation potential. This review shows that solid and non-solid substrate cultivation improves resource utilization efficiency and yield, but substrate sustainability and technical cost need urgent attention. The dynamic regulation of nutrient solution and intelligent management can significantly enhance nutrient absorption efficiency. Rhizosphere microorganisms directly regulate crop health through nitrogen fixation, phosphorus solubilization, and pathogen antagonism. However, the community structure and functional stability of rhizosphere microorganisms in organic systems are prone to imbalance, requiring targeted optimization via synthetic biology methods. Future research should focus on the development of environmentally friendly substrates, the construction of intelligent environmental control systems, and microbiome engineering to promote the expansion of soilless cultivation towards low-carbon, precise, and spatial directions. This paper systematically references the theoretical improvements and practical innovations in soilless cultivation technology, facilitating its large-scale application in food security, ecological protection, and resource recycling.

Root morphology, an important determinant of nutrient absorption and plant growth, can adapt to various growth environments to promote survival. Solution flow under hydroponic conditions provides a mechanical stimulus, triggering adaptive biological responses, including altered root morphology and enhanced root growth and surface area to facilitate nutrient absorption. To clarify these mechanisms, we applied untargeted metabolomics technology, detecting 1737 substances in lettuce root samples under different flow rates, including 17 common differential metabolites. The abscisic acid metabolic pathway product dihydrophaseic acid and the amino and nucleotide sugar metabolism factor N-acetyl-d-mannosamine suggest that nutrient solution flow rate affects root organic acid and sugar metabolism to regulate root growth. Spatial metabolomics analysis of the most stressed root bases revealed significantly enriched Kyoto Encyclopedia of Genes and Genomes pathways: “biosynthesis of cofactors” and “amino sugar and nucleotide sugar metabolism”. Colocalization analysis of pathway metabolites revealed a flow-dependent spatial distribution, with higher flavin mononucleotide, adenosine-5′-diphosphate, hydrogenobyrinic acid, and D-glucosamine 6-phosphate under flow conditions, the latter two showing downstream-side enrichment. In contrast, phosphoenolpyruvate, 1-phospho-alpha-D-galacturonic acid, 3-hydroxyanthranilic acid, and N-acetyl-D-galactosamine were more abundant under no-flow conditions, with the latter two concentrated on the upstream side. As metabolite distribution is associated with function, observing their spatial distribution in the basal roots will provide a more comprehensive understanding of how metabolites influence plant morphology and response to environmental changes than what is currently available in the literature.

This study examined how the nutrient flow environment affects lettuce root morphology in hydroponics using multi-omics analysis. The results indicate that increasing the nutrient flow rate initially increased indicators such as fresh root weight, root length, surface area, volume, and average diameter before declining, which mirrors the trend observed for shoot fresh weight. Furthermore, a high-flow environment significantly increased root tissue density. Further analysis using Weighted Gene Co-expression Network Analysis (WGCNA) and Weighted Protein Co-expression Network Analysis (WPCNA) identified modules that were highly correlated with phenotypes and hormones. The analysis revealed a significant enrichment of hormone signal transduction pathways. Differences in the expression of genes and proteins related to hormone synthesis and transduction pathways were observed among the different flow conditions. These findings suggest that nutrient flow may regulate hormone levels and signal transmission by modulating the genes and proteins associated with hormone biosynthesis and signaling pathways, thereby influencing root morphology. These findings should support the development of effective methods for regulating the flow of nutrients in hydroponic contexts.

The flow of nutrient solutions in hydroponics markedly affects plant growth and development. Suitable flow rates can improve root morphology, facilitating nutrient absorption. Altered cell wall composition upon sensing external stimuli can promote environmental adaptation. Lignin, an important plant cell wall component, enhances structural strength; however, the effects of nutrient solution flow on lignin synthesis remain unexplored. Here, we applied high-throughput metabolomic, transcriptomic, and proteomic techniques to systematically study hydroponically grown lettuce (Lactuca sativa), revealing significant regulatory effects of nutrient solution flow on lignin metabolism in lettuce roots. Gene and protein expression differed in lettuce roots under different flow rates, consistent with the underlying molecular mechanisms elucidated by metabolomic analyses. Specifically, under no-flow conditions, the contents of p-coumaryl alcohols (H-lignin) and coniferyl alcohols (G-lignin) were elevated, whereas high-flow conditions upregulated sinapyl alcohols synthesizing S-lignin. Moreover, lignin synthesis-related HCT, CAD, and PER gene families were highly expressed under no-flow and high-flow conditions, with coordinate changes in lignin content, indicating that nutrient flow influenced their expression; thereby affecting root cell lignin content. This study enhances our understanding of plant growth and secondary metabolic regulatory mechanisms in hydroponic environments and lays a theoretical foundation for optimizing plant growth conditions in hydroponic systems.

The morphology of lettuce roots in hydroponics is affected by the flow environment of nutrient solutions. Regulating the flow rate therefore ensures quality and yield; however, the mechanisms underlying this impact have not been fully elucidated, and breakthroughs in regulatory methods are thus lacking. Herein, lettuce was grown in a hydroponic solution at three different flow rates, the root morphology indicators (such as root length and surface area) were evaluated, the hormone levels of roots grown under different flow conditions were measured, and the correlations between plant hormones and root morphology were analyzed. Transcriptomic analysis was conducted on roots at varying flow rates to investigate the differential expression of genes involved in the synthesis and signal transduction pathways of auxin, abscisic acid (ABA), ethylene, and jasmonic acid. Results showed that these plant hormones were closely related to root morphology. Compared to a non-flow environment, a flow environment promoted the synthesis of plant hormones in the roots and enhanced the signal transduction of certain hormones, such as auxin. However, it had a negative impact on the signal transduction of certain hormones, specifically ethylene. The flow of the nutrients regulated root morphogenesis by influencing the synthesis and transduction of plant hormones, which affected overall plant growth. During the same growth period, lettuce grown under suitable flow conditions had a higher fresh weight than lettuce grown under no-flow conditions. Although such flow would increase the electricity cost of operating water pumps, lettuce could be harvested in advance at appropriate flow rates, thereby reducing the energy consumed in plant factories through lighting and temperature regulation, which are the largest contributors to energy consumption. This study examined the impact of the nutrient solution flow environment as a positive stimulus for plant growth, and it provides a reference for strategically regulating the flow rate in plant factories to improve yield and save energy. Future research should explore the effects of other cultivation and flow methods on the growth of different plants and apply these findings to practical production.

Functional films have been used in greenhouses to improve the light environment for plant growth. A spectrum conversion film (SCF) converting the green light into red light has been introduced to improve the photosynthesis and crop productivity in greenhouses. However, the reasons for the improvement are not fully investigated. The objective of this study was to reveal the effects of the SCF on the electron transport and photosynthetic performance of strawberry. The photosynthetic efficiency, chlorophyll fluorescence, growth, and fruit qualities when the plant was grown under a commercial polyethylene film (PE) and SCF were compared. SCF significantly increased the efficiency of electron transport and the reduction end electron acceptors at photosystems I (PSI) acceptor side. The electron transport rate of PSI and PSII of leaves grown under the SCF were significantly higher than those grown under the PE. Accordingly, the photosynthetic light response curve and photosynthetic rates of leaves increased significantly under the SCF compared to the PE. The growth of strawberry plant was not different, but the fruit weight, sweetness, acidity, and firmness grown under the SCF were significantly improved. These results indicated that the solar spectrum modified by SCF improves electron transport, photosynthetic performance, and fruit quality of the strawberry.

Far-red (FR, 700-800 nm) light has recently been used to regulate phytochrome-mediated morphological re-sponses in vertical farms. Long-term morphological changes in different FR intensities are well known, but changes in photosynthetic capacity have not been sufficiently investigated. The objectives of this study were to quantitatively analyze the growth, photosynthetic responses, and light interception of kale (Brassica oleracea L. var. acephala) depending on the FR fraction. The plants were cultivated at a photosynthetic photon flux density (PPFD) of 240 mu mol m- 2 s- 1 under red and white LEDs with FR LED (peak at 730 nm) for 16 h. The FR fractions determined as FR/R+FR were FR0.07 (control), FR0.28, FR0.60, and FR0.72. To evaluate the morphological and physiological responses in each FR fraction, the growth, chlorophyll content, chlorophyll fluorescence, P700 absorbance change, and photosynthetic rate were measured. Light interception was quantitatively calculated using 3D-scanned plant models with physiological changes and ray-tracing simulations. The dry weight of shoot and root, total petiole length, and leaf area increased with increasing FR fractions. As a result of ray-tracing analysis, the light interception and canopy photosynthetic rate increased with high FR fraction treatment. As the FR fraction increased, the effective quantum yield of photosystem II [Y(II)], the parameters of the JIP test that is related to quantum yield and efficiency for electron transport in photosystem II and photosystem per-formance indices decreased. Despite the decreased electron transport efficiency, the canopy photosynthetic rate increased in relation to the FR fraction. In conclusion, the increase in the FR fraction increased the yield of kale because of the synergistic improvement in morphological change and canopy photosynthesis.

In greenhouses, the higher plant density causes poor light environments inside the canopy due to the mutual shading of adjacent plants. Interlighting has been introduced as a countermeasure to compensate for the lack of light in the middle and bottom canopies. However, most studies have focused on growth and yield, not light use efficiency (LUE) or water use efficiency (WUE). The objective of this study was to evaluate the LUE and WUE of sweet pepper plants subjected to light-emitting diode (LED) interlighting in greenhouses. Two lighting treatments, natural light (control) and supplemental lighting with red and blue LEDs, were applied. Interlighting began 34 days after transplanting. The ratio of red and blue light to photosynthetic photon flux density (PPFD) was 8:2, and the total PPFD was adjusted to 71 μmol m −2 s −1 at a distance of 20 cm. The daily transpiration was measured by subtracting the drainage from the supplied nutrient solution and the weight change of the hydroponic systems. The photosynthetic rate was obtained by measuring light response curves at light intensities of 0, 50, 100, 200, 400, 600, 900, 1200, 1500, and 2000 μmol m −2 s −l . The LUE was calculated based on the simulated light interception obtained by 3D-scanned plant models and ray-tracing simulation. WUE was calculated by dividing the measured dry weight by the accumulated water consumption. Under the interlighting, the LUE increased at the canopy level due to the improved vertical light distributions. The WUE for biomass and fruit yield were higher in the interlighting treatment than in the control. These results were due to the higher increase rates of plant dry weight and fruit yield than that of water consumption by interlighting. In this study, the improvement of LUE and WUE by interlighting could be quantified by optical simulation and a measurement of water consumption throughout the entire growth period.

The principal difference between hydroponics and other substrate cultivation methods is the flowing liquid hydroponic cultivation substrate. Our previous studies have revealed that a suitable flowing environment of nutrient solution promoted root development and plant growth, while an excess flow environment was unfavorable for plants. To explain the thigmomorphogenetic response of excess flow-induced metabolic changes, six groups of lettuce (Lactuca sativa L.), including two flow conditions and three time periods, were grown. Compared with the plants without flow, the plants with flow showed decreased root fresh weight, total root length, root surface area, and root volume but increased average root diameter and root density. The roots with flow had more upregulated metabolites than those without flow, suggesting that the flow may trigger metabolic synthesis and activity. Seventy-nine common differential metabolites among six groups were screened, and enrichment analysis showed the most significant enrichment in the arginine biosynthesis pathway. Arginine was present in all the groups and exhibited greater concentrations in roots with flow than without flow. It can be speculated from the results that a high-flowing environment of nutrient solution promotes arginine synthesis, resulting in changes in root morphology. The findings provide insights on root thigmomorphogenesis affected by its growing conditions and help understand how plants respond to environmental mechanical forces.

Light spectrum is one of the crucial factors that affect the quality and coloration of fruits. This study aimed to analyze how the inter-lighting with red+blue, and/or additional far-red LEDs affects the fruit quality and carotenoid content of red and yellow sweet peppers (Capsicum annuum L.). Three inter-lighting treatments were applied: Natural light (NL), red+blue (RB), and red+blue with far-red (RBFR). The ratio of red and blue was 8:2 in photosynthetic photon flux density (PPFD), and the total PPFD light of inter-lighting sources was adjusted to 70 mu mol m(-2) s(-1) at 20 cm distance. Total soluble sugar, acidity, and firmness were measured as fruit quality indexes. For the measurement of carotenoids, fruits were sampled by dividing them into two harvested groups with different locations in the plants. Group 1 was the first harvested before the plants reached inter-lighting sources, and group 2 was sampled from the location where the light sources were directly illuminated the fruit. Major carotenoid compounds were identified with the High-performance liquid chromatography system based on their absorption maxima and spectrum. Total soluble sugar and firmness were significantly higher in the RB and RBFR in yellow fruits (p<0.05). In group 1, the total carotenoid content was significantly higher in only red fruits in all the inter-lighting treatments, whereas in group 2, the total carotenoids were 3.0-fold and 2.1-fold higher in both red and yellow fruits in the RB, respectively, and 2.0-fold and 1.4-fold higher in the RBFR. In particular, the carotenoid content was about 40% lower in the RBFR than the RB. This study showed that carotenoid compounds could be enhanced by additional inter-lighting in greenhouse cultivation, but far-red wavelengths can lead to a certain level of reduction in total carotenoids.