Effects of the Photoperiod and Photosynthetic Photon Flux Density on the Growth and Production of Justicidin in Justicia procumbens L. via a Vertical Farm

Justicia procumbens L., an annual herb, contains the pharmacologically active compounds justicidin A and B. This study analyzed growth characteristics and bioactive accumulation in response to different lighting conditions using a recirculating deep flow technique (DFT) system in a vertical farm and evaluated the effects of the photoperiod and light intensity level for cultivation.Plants were grown under five treatment combinations consisting of two photoperiods-14 and 16 h-and three photosynthetic photon flux density (PPFD) levels of 200, 300, and 375 µmol•m -2 •s -1 .The D16L375 treatment, with a 16-h photoperiod at 375 µmol•m -2 •s -1 PPFD, produced the greatest biomass, while justicidin production per unit area was comparable to that under D16L300.Plant height reached 35.6 cm, dry weight was 728.9 g•m -2 , and the areal production of justicidin A and B was 1.33 and 0.62 g•m -2 , respectively.Light use efficiency (LUE) and electrical energy use efficiency (EEUE) based on biomass accumulation were also greatest under D16L375, whereas JA-based LUE and EEUE peaked at lower light intensity levels (D16L200 and D16L300, respectively), indicating a trade-off between maximizing biomass and optimizing energy efficiency for bioactive compound production.Dry weight and justicidin A biosynthesis increased linearly with the daily light integral.Consequently, the combination of an extended photoperiod (16 h) and high PPFD (375 µmol•m -2 •s -1 ) proved most efficient for biomass accumulation and bioactive production in J. procumbens.These findings provide fundamental data for designing optimal light environments for the large-scale production of medicinal plants in vertical farming systems.