Artificial Lighting Photoperiod Manipulation Approach to Improve Productivity and Energy Use Efficacies of Plant Factory Cultivated Stevia rebaudiana

Abstract

Stevia rebaudiana cultivated in non-native tropical conditions tends to flower early, halting vegetative growth, resulting in lower biomass and yields of its valued steviol glycoside metabolites. While indoor cultivation allows manipulation of artificial lighting to mimic optimal conditions, it introduces an additional energy cost. The study objectives were to assess photoperiod manipulation as a lighting strategy to increase overall biomass and metabolite yields as well as to improve the efficacy of the electrical energy used for indoor cultivation of Stevia rebaudiana in non-native environmental conditions. Stevia was grown under artificial lighting with red, green, and blue wavelengths with photoperiods of 8 h, 12 h, 16 h, and intermittent light amounting to 16/24 h, each with a constant Daily Light Integral (DLI) of 7.2 mol m−2 day−1. Yield was measured as leaf dry weight biomass in combination with Liquid chromatography–mass spectrometry (LCMS) analysis of Stevioside and Rebaudioside A content. The photon flux density of the artificial and natural light as measured by a spectroradiometer, and the energy use data collected with a three-phase power quality logger, were compared for each treatment tested and to that from plants grown under natural light irradiation in a greenhouse. Yield and energy data were used to determine the efficacies of the lighting systems tested. Stevia plants under a continuous 16-h photoperiod (16H) had the highest productivity, resulting in the highest biomass accumulation and metabolite concentrations. The Stevioside and Rebaudioside A yields per plant were 975% higher than those obtained under natural daylight and day-neutral tropical photoperiod. Overall energy use and photon conversion efficacies were also highest under 16H at 65.10 g kWh−1 for biomass accumulation, 12.40 g kWh−1 for metabolite yields and 7.5 mg mol−1 for photon conversion. These findings support the application of photoperiod manipulation as a viable approach to increase productivity and improve energy use efficacies for indoor cultivation of Stevia rebaudiana plants under artificial lighting in non-native environments with the 16-h photoperiod under red and blue artificial light supplemented with green spectrum as the best option.