Mars regolith simulant as substrate for cultivation of higher plants in Space colonies: the need for organic amendment for potato as a case study

Future long-term space exploration beyond Low Earth Orbit and long permanence of human colonies on solar system planets will depend on the development of specific technologies able to regenerate resources, while minimizing the waste production, and to exploit the resources available in-situ. Bioregenerative Life Support Systems (BLSSs) are artificial ecosystems in which appropriately selected organisms are assembled by combining their metabolic routes in consecutive steps of recycling, to reconvert the crew wastes (carbon dioxide, faeces and urine) into edible biomass, oxygen and potable water. Higher plants represent an optimal tool to renew air through photosynthesis, to purify water through transpiration, and to recover waste products through mineral nutrition, while providing fresh food and health benefits to the astronauts. However, the configuration of fertile substrates for plant cultivation based on extra-terrestrial resources is still a challenge.

Potato (Solanum tuberosum L.) is a candidate crop for space cultivation, based on technical and dietary criteria, including productivity and nutrient composition (content of carbohydrates and proteins). We evaluated the adaptability of potato cv. ‘Colomba’ to the growth on six substrates: the MMS-1 Mars regolith simulant, alone (R100) and in mixture with 30% in vol. of green compost (R70C30), a fluvial sand, alone or mixed with 30% of compost (S100 and S70C30), a red soil from Sicily (RS), and a volcanic soil from Campania (VS). We assessed the physicochemical properties of the substrates, the physiological and biometric parameters, and the nutritional quality of tubers in potato plants grown in pot on in cold glasshouse.

Both R100 and S100 were alkaline (pH ≥8.6) and coarse-textured, lacking organic matter and pivotal macronutrients. The amendment with compost significantly lowered their alkaline pH and improved the chemical fertility. The sandy-loam textured VS was sub-alkaline, slightly calcareous, with higher organic C and nutrient availability than RS. This latter was neutral-to-sub-alkaline, clay textured, poorly calcareous, with significantly higher CEC than VS.

Leaf photosynthesis was higher in plants grown in terrestrial soils and S100. Plant growth was greater in VS, R70C30 and S70C30, while it was reduced on R100. Plants produced healthy tubers on all the substrates.

MMS-1 regolith simulant was found poor in nutrients and unsuitable to sustain adequately the plant growth. Amendment with organic compost improved MMS-1 physiochemical properties and fertility and plant performance.

Keywords: Solanum tuberosum L., controlled environment, Bioregenerative Life Support Systems (BLSSs), in situ resource utilization (ISRU), MMS-1