Basil is best known as an aromatic and medicinal herb due to its rich profile of bioactive compounds. While secondary metabolite production, coupled with growth, has been well studied, photosynthesis has often been overlooked in this regard. In this study, we investigate the effect of light intensities of blue, green, red, and white light of semiconductor LEDs up to 10000 µmol m⁻² s⁻¹ on photosynthetic efficiency and primary and secondary metabolism. Chlorophyll fluorescence data indicate that the conversion of light into chemical energy is the same under green, red, and white light, and 35% increased under blue light. Primary metabolism, represented by assimilation rate, shows that blue light has the lowest assimilation, whereas red and (surprisingly) green light have the highest. Light saturation is reached at 1500 µmol m⁻² s⁻¹, while assimilation under green light is maintained up to 5000 µmol m⁻² s⁻¹. The earliest photoinhibition occurred under blue light in comparison to the other light wavelength under investigation. Blue light also enhances the production of phenolic and flavonoid concentrations up to 40% or 100%, respectively. These results show that photosynthesis, photoinhibition, and secondary metabolite production are wavelength-dependent and indicate how energy fluxes between these processes are related.

This study investigates the effects of ultra-high light intensities and varying light spectra on the photosynthetic efficiency and growth of maize (Zea mays saccharata). Photosynthetic rates, transpiration, stomatal conductance, and leaf temperature were measured under white light, monochromatic light, and their combinations. Assimilation rates increased with light intensities up to 5000 PAR, plateaued around 5500 PAR, and declined beyond 8000 PAR. Red light at 300 PAR yielded the highest assimilation rate under monochromatic conditions, while green light significantly boosted assimilation at higher intensities, peaking at 33.5 µmol m^–2s^–1 under 4000 PAR. A 50% mix of white and green light at 2000 PAR enhanced assimilation by 14% compared to white light alone. Red light (630 nm) notably promoted photosynthesis in high PAR combinations. However, increasing green light reduced quantum yield, and higher blue light enhanced non-photochemical quenching. These findings suggest that ultra-high light intensities with specific spectral combinations can optimize photosynthesis in maize, though this does not necessarily translate to enhanced overall plant growth.

Photosynthetic activity can be monitored using pulse amplitude modulated (PAM) fluorescence or gas exchange. While PAM provides insight into the light-dependent reactions, gas exchange reflects CO₂ fixation and water balance. Accurate, non-invasive prediction of photosynthetic performance under varying conditions is highly relevant for phenotyping and stress diagnostics. Despite their physiological link, data from both methods do not always correlate. To systematically investigate this relationship, photosynthetic parameters were measured in maize (Zea mays, C4) and basil (Ocimum basilicum, C3) under different photon densities and spectral compositions. Maize showed the highest CO₂ assimilation rate of 30.99 ± 1.54 µmol CO₂/(m²s) under 2000 PAR green light (527 nm), while basil reached 10.56 ± 0.92 µmol CO₂/(m²s) under red light (630 nm). PAM-derived electron transport rates (ETR) increased with light intensity in a pattern similar to CO₂ assimilation, but did not reliably reflect its absolute values under all conditions. To improve prediction accuracy, we applied a machine learning model. XGBoost, a gradient-boosted decision tree algorithm, efficiently captures nonlinear interactions between physiological and environmental parameters. It achieved superior performance (R² = 0.847; MSE = 5.24) compared to the Random Forest model. Our model enables accurate photosynthesis prediction from PAM data across light intensities and spectral conditions in both C3 and C4 plants.

This study evaluated the effects of different LED spectral irradiance ratios on the growth, secondary metabolites, and essential oil characteristics of Ocimum x africanum Lour. cultivated for four weeks under controlled conditions. Four LED lighting treatments with different red, blue, green, ultraviolet A, and far red light ratios, and a treatment in greenhouse as control were used. The constant 16-h photoperiod and light intensity of 220 µmol·m-2·s-1 were maintained. The F2 treatment (UV-A:B:R:Fr = 6.60:45.15:29.23:19.02) promoted the greatest plant height (76.62 cm), chlorophyll a (7.41 mg/100 g, FW), chlorophyll b (4.73 mg/100 g, FW), and total phenolic (25.78 mg/g, FW) concentrations. F1 treatment (B:G:R:Fr = 17.14:29.8:47.4:5.66) produced the significantly higher (p < 0.01) biomass (8.3 ton/ha, FW), oil yield (10.89 L/ha), and carotenoid (3.74 mg/100 g, FW) than the others. Essential oils contained 12–15 compounds, dominated by neral (27.5–37.3%), geranial (41.1–49.9%), and (E)-β-caryophyllene (2.4–9.9%). While the highest contents of oil (0.83 %, DW), anthocyanin (16.50 mg/100 g, FW), and total flavonoid (14.17 mg/g, FW) were obtained under F4 (B:G:R:Fr = 13.85:43.50:39.30:3.35). These findings demonstrate that optimized LED spectra can effectively improve both productivity and phytochemical quality in O. africanum through regulating both primary and secondary metabolism.

This study evaluated the effects of different LED spectral irradiance ratios on the growth, secondary metabolites, and essential oil characteristics of Ocimum × africanum Lour. cultivated for four weeks under controlled conditions. Four LED lighting treatments with different red, blue, green, ultraviolet-A, and far-red light ratios, and a treatment in greenhouse as low-light control were used. The constant 16 h photoperiod and light intensity of 220 µmol·m⁻²·s⁻¹ were maintained. The F2 treatment (UV-A:B:R:Fr = 6.60:45.15:29.23:19.02) promoted the greatest plant height (76.62 cm), and chlorophyll a (7.41 mg/100 g, FW), chlorophyll b (4.73 mg/100 g, FW), and total phenolic (25.78 mg/g, FW) concentrations. F1 treatment (B:G:R:Fr = 17.14:29.8:47.4:5.66) produced significantly higher (p < 0.01) biomass (8.3 ton/ha, FW), oil yield (10.89 L/ha), and carotenoid (3.74 mg/100 g, FW) than the others. Essential oils contained 12–15 compounds, dominated by neral (27.5–37.3%), geranial (41.1–49.9%), and (E)-β-caryophyllene (2.4–9.9%), while the highest contents of oil (0.83%, DW), anthocyanin (16.50 mg/100 g, FW), and total flavonoid (14.17 mg/g, FW) were obtained under F4 (B:G:R:Fr = 13.85:43.50:39.30:3.35). These findings demonstrate that optimized LED spectra can effectively improve both productivity and phytochemical quality in O. africanum through regulating both primary and secondary metabolism.