Characterization of the performance of the Higher Plants Chamber in the MELiSSA Pilot Plant under Staggered Operation Mode using Brassica oleracea

Plants will play a pivotal role in future crewed space missions by providing, food, recycling water, and regenerating air. The MELiSSA project develops and integrates a regenerative life support system for long-duration space missions. Its demonstration site, the MELiSSA Pilot Plant, operates a closed-loop of compartments, each with specific functions and interconnected flows. One of these compartments is the Higher Plant Chamber (HPC), a 5 m² chamber primarily tested with Lactuca sativa (lettuce) as a plant model. To broaden the crop portfolio, new experiments were conducted with Brassica oleracea (kale), focusing on oxygen production and physiological responses under two CO₂ concentrations (1,000 ppm and 10,000 ppm). This information is highly relevant for the next stages of the MELiSSA Pilot Plant’s program, specifically the connection of the HPC to other compartments of the MELiSSA. Kale seeds were germinated for 14 days and then transferred to the chamber, where 100 plants were grown hydroponically for 28 days. Plants were grouped into four age (7, 14, 21 and 28) Days after transplant) categories to assess growth over time. Minerals were supplemented via a hydroponic culture system. Under the tested conditions, similar O2 production rates (3 g O2 h-1) were obtained. However, differences of dry biomass and leaf area at harvest were detected between the tests. It can be concluded that the higher CO2 concentration in the gas phase did not compromise the performance of Kale. Kale results were also compared with previous studies using Lettuce. Kale exhibited 1.5 fold higher oxygen production compared to Lettuce, highlighting its potential as a promising crop in biological closed life support systems.