Supplemental lighting is common in northern countries or during winter greenhouse tomato production. We investigated the effect of supplemental lighting treatments on cherry tomato (‘Jun-Ama’) yield, productivity (light-use efficiency (LUE) and energy-use efficiency (EUE)), and fruit quality under high irradiance (average greenhouse daily light integral (DLI) = 14.5 mol m⁻² d⁻¹). Supplemental lighting treatments contained average DLIs of 2.7, 4.9, and 7.6 mol m⁻² d⁻¹ for interlighting, toplighting, and inter- + toplighting, respectively. Supplemental LED lighting increased fruit yield by 18, 41, and 40% with inter-, top-, and inter- + toplighting, respectively, compared with the control. Interlighting increased fruit number (+11%), and top- and inter- + toplighting also increased the fruit number (+26%, +27%) and weight (+10%, +10%), respectively. LUE and EUE were comparable between inter- and toplighting, while inter- + toplighting decreased LUE by 21 and 38%, and EUE by 38 and 31% compared with inter- and toplighting, respectively. All LED supplemental treatments significantly increased total soluble solids compared with the control. Total acidity and lycopene content were unchanged in all treatments. In conclusion, LED supplemental lighting with inter- or toplighting improved cherry tomato yield and quality, but inter- + toplighting was inefficient under high irradiation.

Plant factories with artificial lighting (PFALs), with well-insulated and airtight structures, enable the production of large quantities of high-quality plants year-round while achieving high resource use efficiency. However, despite the controlled environment in PFALs, variations in plant individuals have been found, which affect productivity in PFAL operations. Plant phenotyping plays a crucial role in understanding how the surrounding microenvironment affects variations in plant phenotypes. In the current study, a modular phenotyping system for seedling production was developed, focusing on practicality and scalability in commercial PFALs. Experiments on seedlings, which strongly affect productivity, were conducted to obtain cotyledon unfolding time and the time series projected area of cotyledons and true leaves of individual seedlings of romaine lettuce (Lactuca sativa L. var. longifolia), using RGB images. This was also undertaken to analyze how the surrounding microenvironment of photosynthetic photon flux densities and nutrients affect growth variations for plant cohort research. In agreement with the actual measurements, variations in seedling growth were identified even under similar microenvironments. Furthermore, the results demonstrated larger variations in seedlings with higher relative growth. Aiming for simplified interactions of phenotypes with the microenvironment, management, and genotype, seedling selection and breeding with plant production in PFALs may enable plant uniformity and higher productivity.

Plant phenotyping plays a crucial role in understanding variations in the phenotype of individual plants affected by environment, management, and genotype. Measurement of seed germination is an important phenotyping stage as germination impacts on the whole plant growth process. However, germination measurement has been limited to germination percentage of a seed population. Understanding of the germination time, from sowing to outbreak of the radicle from seed coat, at a single seed level is essential. How individual germination time and further plant growth are affected by its microenvironment and management factors remains elusive. Plant phenotype measurement system was developed to assess individual germination time of romaine lettuce (Lactuca sativa L. var. longifolia), using time-series two-dimensional camera images, and to analyze how microenvironment (volumetric water percent in seed tray, individual seed surface temperature and air temperature) and management factors (coated/uncoated seeds) affect the germination time for plant cohort research, emphasizing practicality in commercial cultivation. Germination experiments were conducted to demonstrate the performance of the system and its applicability for a whole plant growth process in a plant factory for commercial production and/or breeding. The developed phenotyping platform revealed the effects of microenvironment and management factors on germination time of individual seeds.

Chronic kidney disease (CKD) has been a global health problem in recent years. CKD patients often restrict their potassium (K) intake to avoid the high risk of hyperkalemia. In this study, quantitative K management in hydroponics was adopted to produce low K cherry-type tomato (Solanum lycopersicom L.) fruit. The total quantity of K supply per plant during the cultivation was 7.2 g (1 K), 3.6 g (1/2 K), 1.8 g (1/4 K), 0.9 g (1/8 K) and 0.6 g (1/12 K), respectively. The total fruit yield decreased to about 75% at 1/2 K and 58% at 1/12 K compared to 1 K. The fruit K content was lower in 1/4 K, 1/8 K and 1/12 K than in 1 K and 1/2 K, and the fruit from 1/8 K and 1/12 K achieved below 100 mg 100 g⁻¹ FW of K. Total soluble solid content (Brix) was 7–8% in 1 K and 1/4 K but was lower in 1/8 K and 1/12 K. Fruit acid content decreased to 87% in 1/2 K to 70% in 1/4 K and 1/8 K, and to 57% in 1/12 K of 1 K. In conclusion, quantitative K management in hydroponics is expected to produce low K tomato fruit. Fruit K content of approximately 100 mg.100 g⁻¹ FW was achieved when the quantity of K supply was 1/4 K and 1/8 K, with a relatively smaller effect on fruit yield, Brix and acid content.

The recirculating flow hydroponic cultivation unit (RFC) used in plant factories with artificial lighting requires nutrient solution replacement to prevent growth inhibition caused by nutrient imbalances and allelochemical accumulation. Although sustainable systems are needed to reduce environmental impacts, the effects of non-flowing conditions on plant growth and nutrient uptake dynamics remain unclear. We used a one-way, reduced-discharge hydroponic cultivation unit (ORC) to evaluate frill-type lettuce growth and quantify changes in water use efficiency (WUE), fertilizer use efficiency (FUE), and inorganic nutrient absorption under non-flowing conditions. The ORC reduced nutrient solution uptake by ~28% compared with the RFC, improving physiological and system-level WUE and FUE. Root dry weight in the ORC was ~1.5 times higher, likely owing to morphological adaptation—specifically, enhanced root system development—that expanded the nutrient acquisition area under reduced diffusion. Fluid movement in the RFC may also have physically inhibited root growth. Conversely, initial growth in the ORC was lower because of reduced nutrient supply to the rhizosphere. Overall, the ORC achieved high WUE and FUE while minimizing waste. Quantifying the time-course absorption characteristics of inorganic components in this unit is expected to enable precise adjustment of individual nutrients, further reduce discharge, and facilitate high-quality production.