This study examines the impact of daily light integral (DLI) from artificial lighting on tomato seedlings cultivated in plant factories. By adjusting the light intensity and photoperiod of LED, the research explored the effects of varying DLIs on the morphology, growth, physiological characteristics, photosynthetic pigment content, and chlorophyll fluorescence of tomato seedlings. The optimal DLI enhanced seedling growth, biomass, root vitality, antioxidant enzyme activity, and photosynthetic pigment synthesis. Excessively high DLI or light intensity inhibited photosynthesis, potentially leading to photoinhibition. This study identified the optimal DLI of 13.2 mol·m⁻²·d⁻¹ through varying DLI gradients in Exp 1 and Exp 2. Based on these findings, Exp 3 established the optimal growth conditions by setting different light intensities and photoperiods under the most suitable DLI, which were a light intensity of 200 μmol·m⁻²·s⁻¹ and a photoperiod of 18 h. These results provide significant guidance for optimizing the light environment in the cultivation of tomato seedlings in plant factories, helping to improve the light energy utilization efficiency.

Far-red lights (FRs), with a wavelength range between 700 and 800 nm, have substantial impacts on plant growth, especially horticultural crops. Previous studies showed conflicting results on the effects of FRs on vegetable growth and quality. Therefore, we conducted a meta-analysis on the influence of FRs on vegetable growth, aiming to provide a comprehensive overview of their effects on the growth and nutritional indicators of vegetables. A total of 207 independent studies from 55 literature sources were analyzed. The results showed that FR treatment had significant effects on most growth indicators, including increasing the fresh weight (+25.27%), dry weight (+21.99%), plant height (+81.87%), stem diameter (+12.91%), leaf area (+18.57%), as well as reducing the content of chlorophyll (−11.88%) and soluble protein (−11.66%), while increasing soluble sugar content (+19.12%). Further subgroup analysis based on various factors revealed significant differences in the effects of FR on different physiological indicators, such as FR intensity, plant species, duration of FR exposure, and the ratio of red light to FR. In general, moderate FR treatment is beneficial for vegetable growth. This study provides important references and guidelines for optimizing the application of FR in the future.

Crop monitoring can promptly reflect the growth status of crops. However, conventional methods of growth monitoring, although simple and direct, have limitations such as destructive sampling, reliance on human experience, and slow detection speed. This study estimated the fresh weight of lettuce (Lactuca sativa L.) in a plant factory with artificial light based on three-dimensional (3D) reconstruction technology. Data from different growth stages of lettuce were collected as the training dataset, while data from different plant forms of lettuce were used as the validation dataset. The partial least squares regression (PLSR) method was utilized for modeling, and K-fold cross-validation was performed to evaluate the model. The testing dataset of this model achieved a coefficient of determination (R²) of 0.9693, with root mean square error (RMSE) and mean absolute error (MAE) values of 3.3599 and 2.5232, respectively. Based on the performance of the validation set, an adaptation was made to develop a fresh weight estimation model for lettuce under far-red light conditions. To simplify the estimation model, reduce estimation costs, enhance estimation efficiency, and improve the lettuce growth monitoring method in plant factories, the plant height and canopy width data of lettuce were extracted to estimate the fresh weight of lettuce in addition. The testing dataset of the new model achieved an R² value of 0.8970, with RMSE and MAE values of 3.1206 and 2.4576.

This study aimed to determine optimal light recipes for speed breeding of tomato (Solanum lycopersicum L.) in a plant factory. Two tomato cultivars, Zuanhongmeili and Xiaokeai, were investigated. In Experiment 1, conducted under a 12 h photoperiod, both cultivars showed accelerated development with increasing light intensity. The optimal light intensity range of 300–400 μmol·m⁻²·s⁻¹ promoted development and seed maturation. Under these conditions, Zuanhongmeili and Xiaokeai achieved flower bud emergence in the shortest times, at 24.91 ± 0.13 and 24.91 ± 0.12 days after sowing (DAS), respectively. Furthermore, for the two cultivars, anthesis initiation occurred at 39.08 ± 0.62 and 35.78 ± 0.19 DAS, fruit setting at 41.31 ± 0.61 and 38.54 ± 0.24 DAS, and the breaker stage at 83.05 ± 1.05 and 69.78 ± 0.29 DAS, respectively, under these conditions. Critically, germinable seeds were harvested from each cultivar as early as 63 and 60 DAS, projecting a theoretical annual generational turnover of up to six cycles. Based on these results, a baseline irradiance of 350 μmol·m⁻²·s⁻¹ was selected for Experiment 2, which independently assessed the impact of photoperiod. Zuanhongmeili and Xiaokeai both showed accelerated development with increases in photoperiod. The optimal photoperiod of 20 h promoted development and seed maturation. Under a 20 h photoperiod, Zuanhongmeili and Xiaokeai achieved flower bud emergence in the shortest times, at 25.12 ± 0.09 and 23.76 ± 0.13 DAS, respectively. Furthermore, anthesis initiation occurred at 41.21 ± 0.66 and 37.27 ± 0.34 DAS, fruit setting at 44.51 ± 0.15 and 40.25 ± 0.08 DAS, and the breaker stage at 91.19 ± 0.59 and 77.47 ± 0.36 DAS, respectively, under these conditions. The shortest times to harvest of germinable seeds from the two cultivars in this experiment were 76 and 72 DAS. Overall, this study demonstrates that tailored light environments, particularly the light intensity regime identified in Experiment 1, can dramatically accelerate tomato growth and development, enabling production of six generations per year in a controlled environment.

Developing environmentally friendly and cost-effective substrates is critical to enhance resource efficiency and productivity in plant factories with artificial lighting (PFALs). This study employed a molded coconut coir substrate (coconut coir composited with polyurethane hydrophilic adhesive, MCCS) in PFALs to cultivate lettuce (Lactuca sativa L.) and pak choi (Brassica rapa ssp. chinensis). During the transplanting stage, the roots exposed outside the MCCS of lettuce and pak choi were 13.40% and 19.92% shorter, respectively, than in the sponge treatment, and more amenable to mechanical transplanting. This compensated for the neglect of operational efficiency in traditional lifecycle assessment (LCA). Furthermore, compared with sponge and rockwool, MCCS significantly enhanced the yield of lettuce and pak choi by up to 27.33% and 67.19%, respectively. Meanwhile, MCCS significantly increased the chlorophyll content of lettuce compared to sponge by 8.56%. Compared with rockwool, MCCS significantly increased the chlorophyll b content (7.36%), antioxidant content, and antioxidant activity (total phenolics by 13.59%, total flavonoid by 18.43%, FRAP by 12.96%, and DPPH by 19.87%) of lettuce. For pak choi, MCCS increased the soluble protein content in the blade and total phenolics content in the petiole by 32.01% and 14.76%, respectively. More importantly, the use of MCCS led to a significant reduction in the energy consumption per unit area yield of lettuce and pak choi, with maximum reductions of 22.98% and 40.91%, respectively. This eco-friendly substrate is suitable for replacing sponge and rockwool in the production of lettuce and pak choi in PFALs.

In plant factories with artificial lighting (PFALs), spectral regulation serves as the predominant factor governing plant growth and development. The implementation of red-enriched spectral regimens during cultivation promotes biomass accumulation, whereas blue-dominant spectra enhance the biosynthesis of phytochemicals and nutritional compounds in plants. Nevertheless, systematic investigations of staged spectral regimens on both plant development and secondary metabolite biosynthesis remain limited. This study implemented a staged lighting regimen utilizing three distinct red-to-white photon flux ratios (R: W=3:1, 1:1, and 1:3) administered sequentially during critical developmental phases: seedling stage, the early growth stage (15 d after transplanting, DPA), and the late growth stage (16-30 d, DPA) in Pak choi. This study implemented four distinct staged spectral regimens to evaluate photonic treatment effects through multivariate analysis of biomass production, morphological development, photosynthetic pigments, nutritional metabolites, along with antioxidants and radical quenching capacity. The results demonstrated that the T4 treatment significantly enhanced biomass production across all developmental stages. While, the T3 treatment exhibited optimal efficacy in improving nutritional quality (particularly content of soluble proteins and Vitamin C) along with superior antioxidant capacity. The higher red-light significantly enhanced leaf expansion and carotenoid biosynthesis at the seedling stage. While higher blue-light in subsequent growth stages effectively stimulated biosynthesis of chlorophyll and antioxidants. This study established that temporal modulation of red-to-white spectral ratios during vegetative development enabled synergistic optimization of yield and quality attributes in Pak choi.