Effects of daily light integral on tomato (Solanum Lycopersicon L.) grafting and quality in a controlled environment

Tomato (Solanum lycopersicum L. cv. Zhongza NO. 9) was used as the experimental material to investigate the effects of nocturnal LED supplemental light with the photosynthetic photon flux density (PPFD) of 100, 200, 300 μmol·m⁻²·s⁻¹, and the light time of 1, 2 h on the seedling quality in a controlled environment, with seedlings without nocturnal supplemental lighting serving as the control. The results demonstrate that an increase in PPFD at night progressively enhances the plant height and leaf number of tomato seedlings, while stem diameter and leaf area initially increase and subsequently decrease. Although light time and light period-of-time at night did not significantly affect seedling morphology, PPFD and light time notably influenced chlorophyll content and net photosynthetic rate. An optimal lighting energy amount at night augmented photosynthetic capacity. However, excessive PPFD induced photoinhibition in the leaves. Additionally, appropriate nocturnal LED supplemental lighting significantly improved the antioxidant capacity of the seedlings, increased proline content, reduced malondialdehyde content, and bolstered the self-protection mechanisms of the seedlings against nocturnal light stress. Both the PPFD and light time at night promoted biomass accumulation in tomato seedlings. Specifically, when supplemental lighting was applied for 2 h at an intensity of 200 μmol·m⁻²·s⁻¹, both the fresh and dry weights of the shoot and root significantly increased, and the seedling health index was highest. Therefore, appropriate nocturnal LED supplemental lighting positively impacts the health index and photosynthate accumulation of tomato seedlings, but controlling PPFD is essential to avoid photoinhibition.

To achieve high-density tomato seedlings in a plant factory with artificial lighting, tomatoes (Solanum lycopersicum Mill. cv. “Zhongza NO.9”) were used as the experimental material. This study expected to analyze the effects of light intensity (150, 200, 250, and 300 μmol·m⁻²·s⁻¹) and light time (12 and 14 h), as well as daily light integral (DLI, 10.80, 12.60, and 12.96 mol·m⁻²·d⁻¹) and sowing density (50, 72, and 105 holes per tray), on seedling quality. The results indicated that biomass accumulation, seedling quality, and energy use efficiency of seedlings significantly improved with an increase in DLI. At a DLI of 12.96 mol·m⁻²·d⁻¹, seedlings sown at a density of 72 holes per tray exhibited comparable growth characteristics and biomass accumulation to those sown at 50 holes per tray. However, under lower DLIs, seedlings at 50 holes per tray displayed superior growth morphology and seedling quality compared to those at 72 holes per tray. This indicates that increasing the DLI can partially mitigate the negative effects of higher sowing density on seedling quality. Light use efficiency (LUE) and energy use efficiency (EUE) were not significantly different between seedlings at 72 and 105 holes per tray but were higher than those at 50 holes per tray. Therefore, optimizing parameters such as DLI and sowing density can effectively enhance the seedling quality, spatial use efficiency, and light use efficiency in industrial seedling production. Based on the results of this study, a DLI of 12.96 mol·m⁻²·d⁻¹ (achieved with a light intensity of 300 μmol·m⁻²·s⁻¹ and a light time of 12 h) and sowing density of 72 holes per tray are recommended for cultivating high-quality tomato seedlings while reducing energy consumption.

Adding far-red (FR, 700–800 nm) light to photosynthetic active radiation (400–700 nm) proved to be a possible approach to increasing plant biomass accumulation for lettuce production in indoor vertical farms with artificial lighting as a sole-source lighting. However, how FR light addition influences plant growth, development, and metabolic processes and the optimal value of FR photon flux density for greenhouse-grown lettuce under sunlight are still unclear. This work aims to quantify the value of supplementary FR light with different intensities on lettuce morphological and physiological characteristics in a greenhouse. Lettuce ‘Dasusheng’ (Lactuca sativa L.) was grown in a greenhouse under seven light treatments, including white plus red LEDs with FR photon flux density at 0, 10, 30, 50, 70, and 90 µmol m⁻² s⁻¹ (WR, WR + FR10, WR + FR30, WR + FR50, WR + FR70, and WR + FR90, respectively), and lettuce grown with sunlight only was marked as natural light (NL). FR light addition improved the electron transport flux per cross section and performance index (PI_abs, PI_total) and decreased the changes in relative variable fluorescence of lettuce leaves compared to plants under NL. Specifically, the PI_abs of lettuce leaves were 41%, 41%, 38%, 33%, 26%, and 25% lower under control than in plants under treatments WR + FR90, WR + FR70, WR + FR50, WR + FR30, WR + FR10, and WR, respectively. Leaf number, leaf area, and biomass accumulation of lettuce followed a quadratic function with increasing FR light intensity and were the highest under treatment WR + FR50. The shoot fresh weight and dry weight of lettuce were increased by 111% and 275%, respectively, under treatment WR + FR50 compared to NL. The contents of vitamin C, reducing sugar, total soluble sugar, and starch in lettuce showed a similar trend with biomass accumulation. In conclusion, with commonly used photosynthetic photon flux density (PPFD, 400–700 nm) around 200 μmol m⁻² s⁻¹, supplementary FR light intensity of 30~50 μmol m⁻² s⁻¹ was suggested to enhance the photochemistry efficiency, biomass accumulation, and carbohydrates’ contents in greenhouse-grown lettuce.

The terahertz waves are electromagnetic waves with frequencies ranging from 0.1 to 10 THz, exhibiting characteristics of both microwave and infrared, including fingerprint characteristics, coherence, and safety. Due to the weak interactions among most organic macromolecules in substances, the vibrational modes of molecular frameworks, as well as dipole rotation and vibration transitions, often correspond to the terahertz spectral region. Consequently, there has been growing interest in applying terahertz technology within the food industry. This review summarizes the fundamental principles of terahertz spectroscopy for substance detection and highlights recent advances and applications in food analysis. Key applications include harmful contaminant detection, component analysis, quality assessment, and adulteration identification. Additionally, this review discusses current challenges in applying terahertz spectroscopy to food analysis, such as strong water absorption, matrix interference, and the lack of comprehensive spectral databases. Finally, the paper outlines future prospects, including the development of lightweight and cost-effective terahertz sources and detectors for on-site analysis, as well as the integration of terahertz spectroscopy with other modern detection technologies to enhance analytical performance. This work aims to serve as a reference for further research and development of terahertz spectroscopy in the food sector.

Potassium (K⁺) functions as a critical “regulator” and “quality element” in plants, with its physiological roles varying across developmental stages. To clarify the effects of different K⁺ amounts in nutrient solution on water and nutrient absorption characteristics and potassium utilization efficiency in substrate-grown tomato, a controlled experiment was conducted in a climate-regulated solar greenhouse using “Saint Ness” tomato as the plant material. Four K⁺ supply levels (1, 4, 8, and 16 mmol/L, designated as K1, K4, K8, and K16 treatment, respectively) were tested to systematically evaluate the responses of tomato plants at different growth stages in terms of water and nutrient absorption capacity, potassium physiological efficiency (KPE), and potassium utilization efficiency (KUE). The results showed that water absorption capacity did not differ significantly among treatments during the vegetative growth stage. However, during the reproductive stage, the K8 treatment exhibited the highest water absorption capacity (47.05 kg/plant) and water absorption efficiency (84.6%). In addition, K8 significantly promoted the coordinated uptake of K⁺, nitrogen, phosphorus, calcium, and magnesium, with a total potassium absorption capacity of 7.2 g/plant and a potassium absorption efficiency of 79.1%. In contrast, excessive K⁺ supply (16 mmol/L) increased total potassium absorption capacity (5.09 g/plant) but led to a marked decline in physiological efficiency (by 27.9%) and water absorption efficiency (by 10.3%) due to luxury consumption and substrate-induced salt stress. Insufficient K⁺ levels (1–4 mmol/L) also restricted root-mediated water and nutrient flux. The study further revealed a dose-dependent and stage-specific pattern in water and potassium absorption. Therefore, an appropriate K⁺ supply of 8 mmol/L not only improved the plant’s absorption capacity for water and nutrients and potassium utilization efficiency but also maintained ionic balance among essential nutrients. These findings provide a theoretical basis for precision water and fertilizer integration strategies in substrate-cultivated tomato production under greenhouse conditions.