Bioweathering improvement of lunar soil simulant improves the cultivated wheat's seedling length

Abstract

Crewed base is the future trend of lunar exploration. Bioregenerative life support system (BLSS) is necessary for crewed lunar bases, with plant cultivation as the core functional unit. Since transport from the Earth to the Moon is expensive, BLSS should make full use of in situ resources. Lunar soil is the most abundant in situ resource on lunar surface and has little biological toxicity, which could be used as the substrate of plant cultivation in BLSS. However, never experiencing bioweathering process as the Earth's soil, lunar soil has sharp particles at the micro level and thus poor porosity (i.e. poor water holding and aeration capacities) at the macro level. That is, lunar soil's bioavailability for plant cultivation needs to be improved. Imitating bioweathering process, we mixed and co-fermented lunar soil simulant with organic solid waste (composed of plant residues, human feces and microbes) generated by BLSS to improve the bioavailability. Results show that, indicated by the cultivated wheat's seedling length, the bioavailability of lunar soil simulant was significantly (P < 0.05) improved by solid waste and further by fermentation, but optimal solid waste content should be below 0.5% of lunar soil simulant (dry w/w). The significantly (P < 0.05) enriched Na+ during the fermentation was probably released from lunar soil simulant, indicating a successful bioweathering corrosion on lunar soil particles. Consistently, multiple abundant microbial genera reported as able to corrode lunar soil's chemical components were found in the improved substrate. Since the real lunar soil is chemically similar to its simulant, sharp particles of real lunar soil could also be corroded by bioweathering improvement to prevent plant root injury at the micro level, as well as to improve the substrate's porosity at the macro level. This study brings confidence to future lunar soil utilization programs.