Optimizing LED Lighting Spectra and Daily Light Integral for Enhanced Lisianthus Seedling Growth in Vertical Nurseries

Vertical nursery systems offer promising solutions for stable, year-round lisianthus [ Eustoma grandiflorum (Raf.) Shinn.] seedling production. Artificial lighting remains the largest contributor to energy consumption in the operations, underscoring the need to optimize both the light spectra and daily light integral (DLI). Five light-emitting diode (LED) spectral combinations including combinations of red, blue, and far-red light were tested while natural sunlight served as the control. Seedlings grown under the spectral combination of red:blue:far-red at a ratio of 1:1:0.2 exhibited superior shoot and root biomass, larger leaf area, greater stem diameter, higher seedling index, enhanced photon yield (PY), and an improved success rate in mechanical transplantation compared with those associated with other spectral treatments. Far-red supplementation reduced photosynthetic parameters, the net assimilation rate, transpiration rate, electron transport rate, effective quantum yield of photosystem II, and photochemical quenching coefficient. However, it promoted normal shoot elongation after transplantation. In contrast, plants grown under only red and blue light had shortened internodes. Seedling growth exhibited a positive quadratic response to increasing DLI (from 5.18 to 12.96 mol·m −2 ·d −1 ). Most growth parameters peaked at a DLI of approximately 10 mol·m −2 ·d −1 , whereas PY reached its maximum efficiency of 2.3 g·mol −1 photosynthetic photon flux density at a lower DLI of approximately 5.6 to 6.1 mol·m −2 ·d −1 . These findings provide data-driven insights regarding optimizing LED spectra and DLI to enhance the growth of lisianthus seedlings in vertical nurseries.