Abstract
Little is known about how exactly light plays its role in the growth of choy sum (Brassica rapa var. parachinensis), a widely cultivated vegetable in Asia. By applying a commercial soil using black peat as major constituent with 17:10:14 ratio of NPK fertilizer in this study, the growth responses of choy sum seedling to progressively increasing white LED light intensity in an indoor plant factory were investigated, where positive enhancements were observed in choy sum morphology and growth including both dry and fresh mass accumulation under higher light intensity till 400 μmol/(m2⋅s), then a reduction occurred due to light oversaturation and overheat. In indoor plant factory, the inhomogeneous distribution phenomenon of illumination level was inevitably occurred in indoor farm racks generally. For accurately evaluating the productivity of choy sum grown on such racks, a light-time-biomass response model of choy sum seedling grown at the seedling stage was thus established for the first time, which could reliably predict the production outcome of this species in indoor farming practice under various lighting condition and duration. The robustness of the model was further tested by model variation test and sufficient robustness of this model was confirmed. The new insight obtained for the light-dependence of choy sum growth and the light-time-biomass response model can be used to efficiently direct its seedling production in indoor plant factories.
Highlights
The growth of choy sum seedling is strongly dependent on light intensity as we hypothesized
Using Light Emitting Diode (LED) lighting technology, the optimal range of illumination conditions to cultivate choy sum seedling was found to be around 400 μmol/(m2·s), under which the largest leaf area, the best stem architecture with the biggest hypocotyl diameter and the shortest hypocotyl length, the most well-developed root system with the longest root length and the highest root biomass, and a satisfactory photosynthetic efficiency were achieved
The 3D light-time-biomass response model developed can be utilized for reliably predicting the productivity of choy sum seedling in indoor plant factory under inhomogeneous distribution of illumination level of indoor farm racks, by showing excellent model robustness
Summary
The consumption of vegetables has been an integral part of the human diet due to their many health-promoting functions, such as providing dietary fiber as roughage, a variety of bioactive substances, e.g., carotenoids, phenolic compounds, vitamins, and glucosinolates, contained under different levels, as well as their abilities to enhance satiety and promote the absorption of other macronutrients in the intestinal tract (Zhang et al, 2011; Samoulienë et al, 2013; Kwack et al, 2015; Walsh et al, 2015; Peluso et al, 2016; Padayachee et al, 2017; Yahia et al, 2017; Liang et al, 2018; Tan et al, 2020; Huang et al, 2021). Traditional cultivation methods, which account for the bulk of vegetable production, tend to be inefficient and unreliable due to the constant fluctuations in sunlight, which is the main source of light energy for such methods (Alvino and Barbieri, 2016) For this reason, indoor plant factories were being developed for stable and large-scale vegetable productions, and playing an efficient solution for space research and closed agroecosystems in recent years (Fujiwara, 2019; Zhang et al, 2020). The shelf surfaces of cultivation racks of indoor plant factories may undergo inhomogeneous distribution of illumination level due to the arrangement of lamps applied, leading to varied photosynthetic rates and unpredictable productivities of vegetables grown on them. One way of solving this problem is by developing a reliable mathematical model correlating dry mass to light intensity and time corresponding to specific vegetables, to predict their respective productivities in indoor plant factory, which helps farmers to develop a strategy to maximize the efficiencies of photosynthesis and energy conversion in indoor plant factories
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