Effects of LED Lighting Spatial Configuration on Spaceflight Analog Amaranth Crops

Horticultural production is a rapidly developing area of research for the success of long duration NASA space missions. The growth system presently used by NASA for space horticulture utilizes a conventional artificial lighting scheme—i.e., a flat panel of light-emitting diodes (LEDs) situated directly above the plant beds. This results in mutual or self-shading of plants, such that photosynthesis is restricted in the lower canopy and crop yield is reduced. With this in mind, the present work seeks to reduce mutual or self-shading and to maximize yield in densely planted Amaranth beds by optimizing the spatial distribution of LED lighting. Amaranthus tricolor seeds were started in PRO-MIX BX growing media in 5.1 cm trays under T5 high output fluorescent lighting in a lab. After germination, seedlings were moved to one of three lighting treatments utilizing different spatial configurations of red and blue LED lighting strips, each with a photoperiod of 12 hours. In the first treatment (T1), LEDs were arranged such that the source of illumination came from directly overhead. In the second and third treatments (T2 and T3), 60% of the same quantity of LEDs were placed above the plants while 40% were allocated to sidewall or intracanopy configurations, respectively. The data indicated that an intracanopy lighting configuration (T3) increased available light levels for the growing Amaranth without deleterious effects from heat stress. Furthermore, the intracanopy lighting treatment produced crops with increased vegetative biomass, as indicated by leaf size and leaf number as well as plant height. In conclusion, manipulation of crop yield can be accomplished using spatial configuration of lighting with no additional energy inputs or chemical treatments. This investigation is supported by the Hawai’i NASA Space Grant Consortium and provides insight into horticultural practices suitable for long duration spaceflight.