Photosynthesis, plant growth, and fruit production of single-truss tomato improves with supplemental lighting provided from underneath or within the inner canopy

- Both USL and ISL significantly promoted plant development.
- USL maintained relatively stable light irradiation conditions and contributed more to fruit yield.
- ISL induced greater fruit soluble solid contents because of higher exposure to direct supplemental light to fruit.
- ISL induced greater fruit soluble solid contents because of higher exposure to direct supplemental light to fruit.

Light insufficiency is a major abiotic stress limiting plant growth and crop yield in intensive greenhouse production. The application of supplemental lighting to the lower canopy is an efficient method to increase irradiation levels in greenhouse tomato cultivation systems. We evaluated the effects of supplemental lighting provided from underneath the canopy (USL) or within the inner canopy (ISL) on leaf photosynthetic traits, plant growth, and fruit development in single-truss tomato plants. Both USL and ISL significantly promoted leaf photosynthetic activities, plant growth, and fruit production in plants exposed to low solar irradiation levels. The use of USL maintained relatively stable light irradiation conditions in the lower canopy. It also promoted photosynthesis through improved CO2 assimilation and stomatal conductance, and contributed more to fruit yield than ISL. However, ISL induced greater increase in fruit soluble solid contents because of higher exposure to direct supplemental light to fruit. Based on physiological outputs and an energy cost performance analysis, the application of USL may be more financially viable than the use of ISL.