Blue Light Ratio Research Articles

The Impact of Varying Ratios of Light Quality Emitted by Light-Emitting Diodes (LEDs) on the Butter Lettuce

Light-emitting diodes (LEDs) are considered the optimal artificial light source for plant factories, yet further research is needed to understand the impact of LED light quality on plant growth. This experiment investigated the growth and development of butter lettuce under varying ratios of red and blue light provided by LEDs. The specific effects of different red and blue light quality ratios on butter lettuce growth were systematically tracked and recorded, with comprehensive measurements of growth parameters and photosynthetic characteristics. Empirical findings revealed that a higher red light component compared to blue light led to improved butter lettuce characteristics. These included increased leaf length and width, elevated plant height, higher relative chlorophyll content, and an increased net photosynthetic rate. The study also highlighted that the light quality requirements of lettuce fluctuate across different growth stages, allowing for adaptable modulation of lighting conditions to align with specific growth stage needs.Total fresh weight, total dry weight and dry matter content of lettuce reached the highest values in the R8B2 treatment with 80% red light and 20% blue light, and the percentage differences reached 29.2%, 23.1% and 13.9%, respectively. Additionally, the photosynthetic chlorophyll content and net photosynthetic rate exhibited maximum percentage differences of 22.22% and 14.6%, respectively. In conclusion, the experimental evidence supports that an R8B2 spectral composition (80% red and 20% blue light) in a controlled indoor setting represents the optimal light environment for the accelerated growth and superior quality of butter lettuce.

Sole-source Lighting of Lettuce that Increased Yield Had No Negative Effect on Postharvest Longevity

The effects of sole-source lighting on the growth and yield of hydroponically grown lettuce have been extensively studied, but research of postharvest performance is limited. We grew frill-leaf lettuce (Lactuca sativa) ‘Green Incised’ and ‘Hydroponic Green Sweet Crisp’ hydroponically in an indoor vertical research farm under daily light integrals (DLIs) of 12 or 18 mol⋅m−2⋅d−1 and the following three ratios of blue (B; 400–499 nm) and red (R; 600–699 nm) light from light-emitting diode fixtures: B5:R95, B20:R80, and B35:R65. We postulated that biomass accumulation would increase with the DLI and decrease with the B light fraction, and that postharvest longevity would increase with the DLI and the B light fraction. As expected, shoot fresh weight, leaf length and width, leaf number, and relative chlorophyll content (SPAD; ‘Green Incised’ only) decreased as the proportion of B light increased from 5% to 35%. Decreasing the DLI from 18 to 12 mol⋅m−2⋅d−1 reduced the shoot fresh weight and leaf number of both cultivars. Leaves of ‘Green Incised’ were up to 27% wider under B5:R95 and 60% longer under B5:R95 at 12 mol⋅m−2⋅d−1 than those under treatments with a higher DLI or more B light. The shoot fresh weight of ‘Hydroponic Green Sweet Crisp’ was greatest when grown under B5:R95 at 18 mol⋅m−2⋅d−1 and decreased as B light increased or DLI decreased. At the time of harvest, leaves of each cultivar and treatment were placed in clamshells and stored at 7 °C in darkness and evaluated for decay. ‘Green Incised’ that grew under B35:R65 and a DLI of 18 mol⋅m−2⋅d−1 had the shortest storage life, with 9.5 d and 11.4 d for replications 1 and 2, respectively, which were ∼2.5 to 4.0 d and 1.4 to 3.6 d earlier, respectively, than the storage life of lettuce grown under other treatments. In contrast, ‘Hydroponic Green Sweet Crisp’ was not influenced by light quality or DLI and had a storage life of 12.6 to 13.3 d and 13.5 to 14.3 d for replications 1 and 2, respectively. Therefore, a B light fraction between 5% and 20% and a DLI of 18 mol⋅m−2⋅d−1 produced high-yielding frill-leaf lettuce with a relatively long storage life.

Essential oil constituents and secondary metabolites of Mentha viridis under tissue culture technique using violet visible light emitting diodes (LEDs)

This study aimed to propagate the valuable medicinal plant Mentha viridis through in vitro culture of nodal segments measuring approximately 1-1.5 cm. Two different types of light-emitting diode (LED) systems were used to apply three different concentrations of two different cytokinins: 6-benzylaminopurine (BAP) and thidiazuron (TDZ) at 0, 1, or 2 mg/L. The LED systems were white as a control and violet, which is a 1:1 ratio of red and blue light. After a 30-day incubation period, the results revealed significant improvements in the survival rate and the number of shoots per explant across the various treatment groups. With MS medium supplemented with 2 mg/L TDZ and illuminated by white and violet LEDs, the highest values were obtained, yielding survival rates of 93.3% and 13.3 shoots per explant, respectively. Moreover, the treatment involving 2 mg/L TDZ under violet LEDs illumination exhibited superior outcomes in terms of leaf count per explant, callus formation, and callus size. Notably, no callus formation was observed in response to BAP treatments. All treatments resulted in a significant increase in antioxidant enzyme activity and the accumulation of various compounds, such as anthocyanin, ascorbic acid, phenols, flavonoids, peroxidase, and polyphenol oxidase, when compared to the control in a broader context, the levels of IAA, kinetin, and zeatin increased, while GA3 and ABA decreased in response to the applied treatments, as compared to the control. Additionally, ten compounds were consistently found in all treatments by GC/MS analysis of the micro-propagated Mentha, with carvone accounting for the highest proportion (43.5%) and being the predominant component. Among all treatments, nodal segments that were exposed to violet LEDs and grown on MS medium supplemented with 1 mg/L TDZ had the highest carvone content.

Study on the photosynthetic growth characters in Cimicifuga dahurica (Turcz.) Maxim under different supplemental light environments

Cimicifuga dahurica (C. dahurica) is an important medicinal plant in the northern region of China. The best supplemental light environment helps plant growth, development, and metabolism. In this study, we used two-year-old seedlings as experimental materials. The white light as the control (CK). The different ratios of red (R) and blue (B) combined light were supplemented (T1, 2R: 1B, 255.37 μmol m−2·s−1; T2, 3R: 1B, 279.69 μmol m−2·s−1; T3, 7R: 1B, 211.16 μmol m−2·s−1). The growth characteristics, photosynthetic pigment content, photosynthesis and chlorophyll fluorescence parameters, and primary metabolite content were studied in seedlings. The results showed that: 1) The fresh weight from shoot, root, and total fresh weight were significantly (P < 0.05) increased under T2 and T3 treatment. 2) The contents of chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll (Chl) were significantly (P < 0.05) increased under T2 treatment, and carotenoid (car) content was reduced. 3) The photochemical quenching (qP), the actual photosynthetic efficiency of PSII (Y(II)), and the photosynthetic electron transfer rate (ETR) from leaves were significantly (P < 0.05) increased under T1 treatment. The Net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr) were significantly (P < 0.05) increased under T2 and T3 treatments. 4) A total of 52 primary metabolites were detected in C. dahurica leaves. Compared with CK, 14, 15, and 18 differential metabolites were screened under T1, T2, and T3 treatments. In addition, D-xylose, D-glucose, glycerol, glycolic acid, and succinic acid were significantly (P < 0.05) accumulated under the T2 treatment, which could regulate the TCA cycle metabolism pathway. The correlation analysis suggested that plant growth was promoted by regulating the change of D-mannose content in galactinol metabolism and amino sugar and nucleotide sugar metabolism. In summary, the growth of C. dahurica was improved under T2 treatment.

Blue light regulated lignin and cellulose content of soybean petioles and stems under low light intensity.

To improve light harvest and plant structural support under low light intensity, it is useful to investigate the effects of different ratios of blue light on petiole and stem growth. Two true leaves of soybean seedlings were exposed to a total light intensity of 200μmolm-2 s-1 , presented as either white light or three levels of blue light (40μmolm-2 s-1 , 67μmolm-2 s-1 and 100μmolm-2 s-1 ) for 15days. Soybean petioles under the low blue light treatment upregulated expression of genes relating to lignin metabolism, enhancing lignin content compared with the white light treatment. The low blue light treatment had high petiole length, increased plant height and improved petiole strength arising from high lignin content, thus significantly increasing leaf dry weight relative to the white light treatment. Compared with white light, the treatment with the highest blue light ratio reduced plant height and enhanced plant support through increased cellulose and hemicellulose content in the stem. Under low light intensity, 20% blue light enhanced petiole length and strength to improve photosynthate biomass; whereas 50% blue light lowered plants' centre of gravity, preventing lodging and conserving carbohydrate allocation.

Effects of light qualities on growth and physiological-biochemical traits of Scutellaria baicalensis.

Canopy spectral composition significantly affects growth and functional traits of understory plants. In this study, we explored the optimal light condition suitable for enhancing Scutellaria baicalensis's yield and quality, aiming to provide scientific reference for the exploitation and utilization of medicinal plant resources in the understory of forests. We measured the responses of growth, morphology, biomass allocation, physiological traits, and secon-dary metabolites of S. baicalensis to different light qualities. S. baicalensis was cultured under five LED-light treatments including full spectrum light (control), ultraviolet-A (UV-A) radiation, blue, green, and red light. Results showed that UV-A significantly reduced plant height, base diameter, leaf thickness, leaf area ratio, and biomass of each organ. Red light significantly reduced base diameter, biomass, effective quantum yield of photosystem Ⅱ (ФPSⅡ), and total flavonoid concentration. Under blue light, root length and total biomass of S. baicalensis significantly increased by 48.0% and 10.8%, respectively, while leaf number and chlorophyll content significantly decreased by 20.0% and 31.6%, respectively. The other physiological and biochemical traits were consistent with their responses in control. Our results suggested that blue light promoted photosynthesis, biomass accumulation, and secondary metabolite synthesis of S. baicalensis, while red light and UV-A radiation negatively affected physiological and biochemical metabolic processes. Therefore, the ratio of blue light could be appropriately increased to improve the yield and quality of S. baicalensis.

Identifying the critical LED light condition for optimum yield and flavonoid of pea sprouts

Light, as an energy source and environmental signal, can significantly impact plant growth, development, and metabolism. This study explored three aspects of light environment, including light quality (different red and blue combination), intensity (9–90 μmol/m2/s), and photoperiod (4–20 h/d) to identify and utilize the optimal light conditions for promoting morphogenesis and the accumulation of phenolic compounds in pea (Pisum sativum L.) sprouts of variety Taiwanxiaobaihua. The results showed that dark conditions and red light promoted the longitudinal growth of pea sprouts, while blue light had an inhibitory effect. The appropriate ratio of red and blue light could positively affect the morphological establishment of pea sprouts, promoting the accumulation of total phenolic and total flavonoid contents and improving the antioxidant properties. Within a certain light range, the total flavonoid content and total flavonoid yield of pea sprouts showed an increasing trend with the light intensity increase and the photoperiod extension. Precise estimation of optimal light parameters was achieved using regression models, the total flavonoid content, total flavonoid yield, and dry matter mass of pea sprouts reached an optimal amount at red/blue light ratios of 0.33, 0.46, and 0.71, at 105.86, 90.00, and 9.00 μmol/m2/s of light intensity and at 32.33, 23.28 and 8.23 h/d of photoperiod, respectively. Specifically, increasing dry matter mass by 1 mg decrease in total flavonoid content by 0.78 mg in pea sprouts under these conditions. The scientifically guided light regulation technologies can improve the yield and quality of sprouts and provide a scientific basis for the sustainable development of the sprout industry.

Several short-day species can flower under blue-extended long days, but this response is not universal

Sole-source LED lighting enables spectral flexibility to achieve desirable plant characteristics and product quality. An earlier study from our lab showed that short-day plant chrysanthemum flowers normally under long days with dynamic lighting of 11 h dichromatic red-blue LED light extended with 4 h sole blue LED light. Such dynamic LED lighting is possible in vertical farms and opens the possibility to supply a higher daily light integral (DLI) to short-day plants by providing more hours of light and thus increase growth rate. This study aims to investigate for several short-day species whether normal flowering is obtained when 11 h of red-blue is extended with 4 h of sole blue LED light. Twelve genotypes of nine short-day plants species (kalanchoe - Kalanchoe blossfeldiana, perilla - Perilla frutescens, stevia - Stevia rebaudiana, artemisia - Artemisia annua, chrysanthemum - Chrysanthemum seticuspe and Chrysanthemum morifolium, cosmos - Cosmos bipinnatus, poinsettia - Poinsettia pulcherrima and wild tomato - Solanum habrochaites) were grown at three light conditions in a climate room: 11 h red-blue short day, 11 h red-blue extended with 4 h of sole blue, and 15 h red-blue long day. Mixed red and blue light (ratio 60:40) was provided at a total photosynthetic photon flux density (PPFD) of 100 µmol m−2 s−1 and sole blue light was provided at 40 µmol m−2 s−1 PPFD. Flowering response differed among species: kalanchoe, perilla and stevia flowered only in red-blue short day. Artemisia, chrysanthemum, cosmos, poinsettia, and wild tomato flowered in red-blue short day, and blue-extended long day but not in red-blue long day. However, there was a flowering delay in cosmos, poinsettia, and wild tomato under blue-extended long days compared to short days. In blue-extended long days plants received 15 % higher DLI resulting in a 4 to 36 % increase in total dry weight compared to short days. This study shows that increasing growth rate under light-limiting growth conditions through daylength-extension with sole blue light, without compromising flowering and quality, is possible for some, but not all short-day species.

Growth responses of tomato plants to different wavelength ratios of amber, red, and blue light

The differential effects of light quality and quantity are under scrutiny so that energy-efficient plant production may be optimized. This study aimed to determine the combined effects of amber (595 nm), red (635 nm), and blue (445 nm) wavelengths at different light intensities on tomato plant growth. Plants were treated for 12 days with combined light-emitting diode (LED) wavelengths, at a photosynthetic photon flux density (PPFD) ranging from 232 to 1660 μmol m−2s−1 with a 16 h d−1 photoperiod. Mean fresh mass of tomato plants treated with amber-red light (AR) was 22% greater than plants treated with blue-amber (BA) light and 67% greater than blue-red (BR) light. Plants treated with BA exhibited 36% greater fresh mass than plants treated with BR light. Mean dry mass of plants treated with AR light was 30% greater compared to BR light, and the dry mass of plants treated with BA and BR was statistically similar. Plants grown under BR had 28% and 35% smaller leaf area compared with those grown under BA and AR, respectively. Mean height of the plants treated with AR increased by 24 and 52% compared to plants grown under BA and BR lights, respectively. Maximum stem diameter was observed at 1000 μmol m−2s−1 for AR and BA, and 1200 μmol m−2s−1 for BR. Specific leaf area (SLA) decreased with the increase of PPFD levels up to 1000 μmol m−2s−1 for all the light treatments. A PPFD above 1000 μmol m−2s−1 showed an increase in SLA for plants cultivated with AR and AB. SLA for plants treated with RB was stable above 1000 μmol m−2s−1 PPFD levels. Plants treated with BR light had 25 and 38% higher chlorophyll content compared to plants treated with BA and AR light, respectively. Maximum yield and chlorophyll content data indicate that using Chl content to correlate full plant photosynthetic and growth potential is inappropriate. Findings suggest that a high percentage of amber light (>75%) in a full-spectrum LED regimen may augment controlled environment crop production.

Effect of Different Ratios of Red and Blue Light on Maximum Stomatal Conductance and Response Rate of Cucumber Seedling Leaves

Light can regulate leaf stomatal development and movement, but the effects of different red-to-blue light mass ratios on leaf stomatal morphology and openness are not fully understood. In this trial, five different red-to-blue light (R:B) ratio treatments were used to study the changes in morphology, photosynthesis, and stomatal-related indexes of cucumber seedlings under fixed light intensity (200 μmol·m−2·s−1). The results showed that the thickness of spongy tissue and stomatal size (SZ) of cucumber seedling leaves decreased, and the photosynthetic potential, stomatal density (SD), maximum stomatal conductance and stomatal responsiveness increased with decreasing R:B content. The experimental results showed that when R:B = is 1:9, cucumber seedlings had the greatest stomatal density and the fastest response rate, and the stomatal opening rate was accelerated with the increase in the proportion of blue light; when R:B = is 3:7, the stomatal conductance was the greatest and the net photosynthetic rate was the highest. This trial provides some implications for changing plant light quality and thus affecting stomatal development and movement.

Effects of red and blue light ratio on the morphological traits and flower sex expression in Cucurbita moschata Duch.

Squash (Cucurbita moschata Duch.) is an important fruit vegetable that can be long-term transport and storage. Light-emitting diodes (LEDs) are commercially used light sources applied to improve the producing of leaf vegetables in plant factory. However, the influences of LEDs on the plant growth and flower development of fruit vegetables remain unknown. In this study, five effective light quality treatments, including white light, a 10:8 ratio of blue (B) to red (R) light, a 10:4 mixture of blue/red light, red light, and blue light, were used for growing squash and inducing female flowers to maximize production. Our results show that varying light quality influence morphological traits and flower appearance. Both blue and red light improved the development of first and second internodes and induced larger leaves and petiole lengths, whereas 10:4 mixture caused shorter plant heights and decreased internode and petiole lengths. Although 10:8 mixture treatment reduced chlorophyll content, this spectral regime increased leaf number and influenced flower sex development, inducing more female flowers and more fruits. Light quality manipulation thus beneficially influences the growth and flower sex proportion in squash plants. Squash plants under 10:8 mixture treatment exhibited increase in yield, and can be used as a supplementary light treatment in plant factory.

Beneficial effects of red and blue light on potato leaf antioxidant capacity and tuber bulking.

Artificial light application is an effective method for promoting potato production in indoor facilities. In this study, we assessed the effects of different combinations of red (R) and blue (B) light application on potato leaf and tuber growth. Potato plantlets were transplanted under W (white light, control), RB5-5 (50% R + 50% B), RB3-7 (30% R + 70% B to 70% R + 30% B) and RB1-9 (10% R + 90% B to 90% R + 10% B), and ascorbic acid (AsA) metabolism in leaves and cytokinin (CTK), auxin (indole-3-acetic acid, IAA), abscisic acid (ABA), and gibberellin (GA) levels in tubers were measured. At 50days of treatment, potato leaves had significantly higher L-galactono-1,4-lactone dehydrogenase (GalLDH) activity and utilized AsA faster under RB1-9 treatment than under RB3-7 treatment. CTK/IAA and ABA/GA ratios in large tubers under W treatment did not differ significantly from those under RB1-9 treatment, which had higher levels than those under RB5-5 and RB3-7 treatment at 50days. However, under RB1-9 treatment, total leaf area decreased rapidly from 60 to 75days compared with plants under RB3-7 treatment. Tuber dry weight per plant under W and RB5-5 treatment approached a plateau at 75days. At 80days, RB3-7 treatment significantly improved ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase activity compared with RB1-9 treatment. RB1-9 treatment with a high ratio of blue light increased CTK/IAA and ABA/GA to improve tuber bulking at 50days, while RB3-7 treatment with a high ratio of red light stimulated AsA metabolic pathway to delay leaf oxidation and maintain tuber biomass accumulation at 80days. For the indoor potato cultivation, RB3-7 treatment had a higher proportion of medium-sized tubers, thus being a suitable light treatment.

A Novel LED Light Radiation Approach Enhances Growth in Green and Albino Tea Varieties.

Light, as an energy source, has been proven to strongly affect photosynthesis and, thus, can regulate the yield and quality of tea leaves (Camellia sinensis L.). However, few comprehensive studies have investigated the synergistic effects of light wavelengths on tea growth and development in green and albino varieties. Thus, the objective of this study was to investigate different ratios of red, blue and yellow light and their effects on tea plants' growth and quality. In this study, Zhongcha108 (green variety) and Zhongbai4 (albino variety) were exposed to lights of different wavelengths for a photoperiod of 5 months under the following seven treatments: white light simulated from the solar spectrum, which served as the control, and L1 (red 75%, blue 15% and yellow 10%), L2 (red 60%, blue 30% and yellow 10%), L3 (red 45%, far-red light 15%, blue 30% and yellow 10%), L4 (red 55%, blue 25% and yellow 20%), L5 (red 45%, blue 45% and yellow 10%) and L6 (red 30%, blue 60% and yellow 10%), respectively. We examined how different ratios of red light, blue light and yellow light affected tea growth by investigating the photosynthesis response curve, chlorophyll content, leaf structure, growth parameters and quality. Our results showed that far-red light interacted with red, blue and yellow light (L3 treatments) and significantly promoted leaf photosynthesis by 48.51% in the green variety, Zhongcha108, compared with the control treatments, and the length of the new shoots, number of new leaves, internode length, new leaf area, new shoots biomass and leaf thickness increased by 70.43%, 32.64%, 25.97%, 15.61%, 76.39% and 13.30%, respectively. Additionally, the polyphenol in the green variety, Zhongcha108, was significantly increased by 15.6% compared to that of the plants subjected to the control treatment. In addition, for the albino variety Zhongbai4, the highest ratio of red light (L1 treatment) remarkably enhanced leaf photosynthesis by 50.48% compared with the plants under the control treatment, resulting in the greatest new shoot length, number of new leaves, internode length, new leaf area, new shoot biomass, leaf thickness and polyphenol in the albino variety, Zhongbai4, compared to those of the control treatments, which increased by 50.48%, 26.11%, 69.29%, 31.61%, 42.86% and 10.09%, respectively. Our study provided these new light modes to serve as a new agricultural method for the production of green and albino varieties.

Morphological and Physiological Traits of Greenhouse-Grown Tomato Seedlings as Influenced by Supplemental White Plus Red versus Red Plus Blue LEDs

The relatively low light intensity during autumn–winter or early spring and inclement weather such as rain or fog may lead to extended production periods and decreased quality of greenhouse-grown tomato seedlings. To produce high-quality tomato seedlings rapidly, the influences of supplementary lights with different spectra on the morphological and physiological traits of tomato seedlings were measured in a greenhouse. Supplemental lighting with the same daily light integrals (DLI) of 3.6 mol m−2d−1 was provided by white (W) light-emitting diodes (LEDs), white plus red (WR) LEDs, and red plus blue (RB) LEDs, respectively, and tomato seedlings grown under only sunlight irradiation were regarded as the control. Our results demonstrate that raised DLI by supplementary light improved the growth and development of greenhouse-grown tomato seedlings, regardless of the spectral composition. Under conditions with the equal DLI, the tomato seedlings grown under supplementary WR LEDs with a red to blue light ratio (R:B ratio) of 1.3 obtained the highest values of the shoot and root fresh weights, net photosynthetic rate, and total chlorophyll content. The best root growth and highest root activity of tomato seedlings were also found under the supplementary WR LEDs. Supplementary WR LEDs remarkably increased the stem firmness of the greenhouse-grown tomato seedlings, and increased the starch content in the leaves of greenhouse-grown tomato seedlings compared to the control. However, statistically significant differences did not occur in the sucrose, carotenoid contents, superoxide dismutase (SOD), and catalase (CAT) activities among the different supplemental lighting treatments. In conclusion, supplemental LED lighting could promote the growth and development of greenhouse-grown tomato seedlings grown under insufficient sunlight conditions. In addition, WR LEDs could obtain tomato seedlings with a higher net photosynthetic rate, higher root activity, and higher starch content compared with other treatments, which could be applied as supplementary lights in greenhouse-grown tomato seedlings grown in seasons with insufficient light.

Effect of different LED-lighting quality conditions on growth and photosynthetic characteristics of saffron plants (Crocus sativus L.)

The effects of different light-emitting diode (LED) lights on saffron growth and photosynthetic characteristic were explored. Physiological mechanisms were explained by chlorophyll a fluorescence transient curves (OJIP) and JIP-test parameters. A decrease in the red to blue light ratio resulted in negative effects, particularly for monochromatic blue (B) LED light; saffron seedlings showed reduced chlorophyll accumulation, inhibited leaf elongation, and decreased photosynthetic performance. In the OJIP curve, the higher positive K-band observed for B LED light indicated that oxygen-evolving complex activation significantly decreased. B LED light inhibited the electron transport between primary quinone acceptor and secondary quinone acceptor as well as the existence of reducing plastoquinone centers, and increased energy dissipation of reaction centers. Otherwise, the red to blue light ratio of 2:1 had a positive effect on saffron cultivation, resulting in the longest leaf lengths, highest chlorophyll content, and photosynthetic characteristics. This study provides theoretical guidance for saffron agricultural practices.

Red to Blue Light Ratio and Iron Nutrition Influence Growth, Metabolic Response, and Mineral Nutrients of Spinach Grown Indoors

Leafy greens are increasingly being produced indoors with electric lighting from light-emitting diodes (LEDs). Red (R) and blue (B) LEDs are commonly used to ensure healthy plant growth, but biofortification techniques can potentially maximise nutritional quality. The aim of the study was to evaluate the effects of B (peak = 450 nm) and R (peak = 665 nm) light ratios (R:B) of 9:1, 3:1, and 1:3 on growth, metabolic response, and the accumulation of mineral nutrients in spinach ‘Corvair F1’ and ‘Space F1’ grown in hydroponic solutions with different iron (Fe) concentrations (2, 5, and 15 mg L−1). Plant biomass and leaf length, width, and number generally decreased as the R:B decreased, leading to a high concentration of Fe in the solution. A higher Fe dose increased the contents of some other minerals but depended on the R:B and cultivar. For example, Zn generally increased with increasing Fe but Cu content decreased, especially in ‘Space F1’. There were less-profound effects of the R:B and Fe dose on metabolites or antioxidant capacity. The research findings suggest that the overall nutritional quality of spinach could improve with lighting and Fe biofortification strategies and thus increase the sustainability of indoor crop production.

Affordable phosphor-converted LEDs with specific light quality facilitate the tobacco seedling growth with low energy consumption in Industrial Seedling Raising.

Industrial Seedling Raising (ISR) is increasingly becoming an important part of Modern Agriculture because of its efficient utilization of land, water, and fertilizer as well as its advantages of being not easily affected by the weather. However, the high cost and high energy consumption of light sources for plant growth is limiting the popularization of ISR technology. Phosphor-converted light-emitting diodes (pc-LEDs) make use of relatively affordable red phosphor and blue light chips, providing an adjustable spectrum to optimize plant growth. To identify the energy-saving light quality of pc-LEDs, we investigated the effects of a variety of light qualities on the growth of tobacco seedlings. Y3Al5O12:Ce3+, CaAlSiN3:Eu2+, KAl11O17:Eu2+ phosphors were combined with the blue light chip according to different proportions to produce the following light sources: CK (white light), T1 (blue light), T2 (red light), T3 (red: blue light ratio=1:4), T4 (red: blue light ratio=4:1). The tobacco variety Xiangyan7 grown continuously under T1, T2, T3, and T4 significantly increased the leaf area, stem length, biomass, root area and main root length compared with those grown under white light. Among the five kinds of light qualities tested, T4 treatment exerted the best effect on leaf development and biomass increase, while T2 exerted the best effect on stem elongation. The cytological analysis demonstrated that the promotion of the cell size and cell number of leaf epidermal cells by T1-T4 might contribute to the leaf expansion. Further analysis at the molecular level suggested that the light quality affected the RNA levels of the genes involved in cell division and expansion. When tobacco seedlings reached the same biomass, T1-T4 light sources saved 71%, 86%, 80% and 89% of electric energy respectively compared with white light. Therefore, the application of specific pc-LEDs not only reduces the cost of light source production, but also saves energy consumption, offering great potential for ISR technology to cut costs and increase efficiency.

Effects of light spectrum on the morphophysiology and gene expression of lateral branching in Pepino (Solanum muricatum).

In the present study, we determined the morphological and physiological indicators of Pepino to elucidate its lateral branching responses to different light qualities using a full-spectrum lamp (F) as the control and eight different light ratios using blue light (B) and red light (R). In addition, correlation analysis revealed that the gene expression patterns correlated with lateral branching under various light treatments. Compared with the F treatment, the R treatment increased the plant height and inhibited the elongation of lateral branches, in contrast with the B treatment. The number of lateral branches did not change significantly under different light quality treatments. Moreover, correlation analysis showed that the ratio of blue light was significantly positively correlated with the length of lateral branches and significantly negatively correlated with plant height, aboveground dry weight, and other indicators. We conducted transcriptome sequencing of the sites of lateral branching at three periods under different light quality treatments. The gene related to photodynamic response, cryptochrome (CRY), was the most highly expressed under B treatment, negatively regulated lateral branch length, and positively correlated with plant height. Branched 1, a lateral branch regulation gene, was upregulated under R treatment and inhibited branching. Overall, the red light facilitated internode elongation, leaf area expansion, plant dry weight increase, and inhibition of lateral branching. Soluble sugar content increased, and the lateral branches elongated under blue light. Different light qualities regulated lateral branching by mediating different pathways involving strigolactones and CRY. Our findings laid a foundation for further clarifying the response mechanism of Pepino seedlings to light and provided a theoretical reference for elucidating the regulation of different light qualities on the lateral branching of Pepino.

Effect of blue light intensity and photoperiods on the growth of diatom Thalassiosira pseudonana

Diatom Thalassiosira pseudonana photosynthetic properties and generation of fucoxanthin and lipid production under different blue light intensity with different photoperiods (dark/light cycle) at temperature 23 ± 1 °C were studied in this work. The growth (cell number) and the biomass concentration of the cells were found to be doubled at 120 μE m−2 s−1 blue light intensity as compared to 200 μE m−2 s−1 at 8:16 h dark light photoperiods. The rise in blue intensity from 40 to 120 μE m−2 s−1 has increased the synthesis of fucoxanthin and lipid in Thalassiosira pseudonana at dark-light cycle 8:16 h. It was found that at optimal amount of blue light and photoperiod ratio, evidently influence the growth of Thalassiosira pseudonana by yielding 35.6 % lipid and 1.18 mg/g fucoxanthin.

The Influence of Red and Blue Light Ratios on Growth Performance, Secondary Metabolites, and Antioxidant Activities of Centella asiatica (L.) Urban

This study aimed to determine the optimal light conditions for the protected cultivation of Centella asiatica—a herbaceous medicinal plant with high bioactive content and antioxidant potential. The growth, triterpene glycoside content, total phenol content (TPC), total flavonoid content (TFC), and antioxidant activities of seedlings grown for five weeks under different light intensities (150 and 200 μmol m−2 s−1) and qualities (red and blue light ratios: 10:0, 8:2, and 6:4) were evaluated. Light intensity and quality significantly affected the studied parameters. At 150 μmol m−2 s−1 photosynthetic photon flux density (PPFD), most growth parameters decreased as the blue light ratio increased; however, the plants showed extreme epinasty under the sole red light treatment. Growth performance was highest under 20% blue light and 200 μmol m−2 s−1 PPFD. At both light intensities, the total triterpene glycoside content was higher for the sole red light and 20% blue light treatments than the 40% blue light treatment. Moreover, the TPC, TFC, and antioxidant activity increased as the blue light ratio increased. In conclusion, artificial light conditions affect the growth and secondary metabolite production of C. asiatica differentially, and 20% blue light at a higher light intensity (200 μmol m−2 s−1) is optimum for growing C. asiatica.