Bioregenerative life support systems (BLSSs) will be essential in long-term space missions to reduce the requirement for supplies from the Earth. Most of these BLSSs will include crops to generate oxygen (O 2), water, and food needed by the astronauts, while capturing carbon dioxide (CO 2) from the atmosphere. While previous research studies have shown that plants provide these services when grown under optimal mineral nutrition, we consider it also important to study the impact of suboptimal plant nutrition as any decrease in O 2, water, and food production or CO 2 capture could have long-term effects in the BLSS. To this end, we conducted four crop tests in the Plant Characterization Unit (PCU) of the European Space Agency, located at the University of Naples Federico II, examining the impacts of adding sodium chloride (NaCl) and reducing potassium (K) in nutrient solutions on lettuce (Lactuca sativa L. ). The control treatment with the standard nutrient solution composition was run twice (Control₁ and Control₂) to investigate the repeatability of the PCU crop tests. Plant growth during the experiment was monitored by quantifying O 2 and water production, the projected leaf area, and canopy temperature throughout the crop tests. At harvest, photosynthesis-related parameters (F v /F m, SPAD, stomatal conductance, and transpiration rate) were collected, and the leaf, stem, and roots were weighed and analyzed for total elemental composition. Assessing the impact of the suboptimal mineral nutrition on plants was challenged by high plant-to-plant variability within each test. Furthermore, considerable differences in plant growth were observed in the two control treatments. Comparisons with previous and similar experiments suggested that Control₂ provided a more realistic representation of the control treatment. Compared to Control₂, the addition of 27 mM NaCl in the nutrient solution did not result in any significant decrease in biomass production, or in photosynthesis-related parameters at harvest. The net water and O 2 productions were also comparable to those observed in Control₂. However, the projected leaf area showed decreased plant development compared to Control₂. The reduction in K in the nutrient solution decreased plant development, as reflected in the projected leaf area, and a 20% decrease in shoot dry biomass. This, in turn, led to led to a decrease in O 2 and water production of the PCU relative to Control₂. Our results show that a nutrition strategy that is not adapted to plant needs can lead to decreased plant performance in BLSSs. The impact of such a decrease on the sustainability of long-duration crewed Space missions will need to be studied.
Pellegri et al. (Thu,) studied this question.