Positive effects and mechanisms of simulated lunar low-magnetic environment on earthworm-improved lunar soil simulant as a cultivation substrate

With the advancement of crewed deep-space exploration missions, Bioregenerative Life Support Systems (BLSS) for lunar-surface bases has become crucial, which would face the stresses from lunar in situ environmental factors. Compared to microgravity and long-term low-dose ionizing radiation, the low-magnetic field is difficult to simulate in Earth-based experiments. However, it may not necessarily act as a stress for BLSS biological components, so elucidating it may significantly simplify the subsequent research. Earthworms, known as “soil scavengers”, have been proved as efficient in improving lunar soil simulant as a plant cultivation substrate and the degradation-recycling of inedible lignocellulosic plant residues by our previous studies. This study applied earthworms to a mixed substrate of lunar soil simulant and the organic solid waste (from our “Lunar Palace 365″ crewed long-term closed BLSS experiment) under three magnetic conditions: lunar low-magnetic (5 nT), Earth-magnetic (25–65 μT), and high-magnetic (7,000 μT). Results showed that stronger magnetic fields significantly increased the earthworms' oxidative stress levels (MDA) and impaired neurotransmitter levels (Ca²⁺/Mg²⁺-ATPase and acetylcholine). Consistently, weaker magnetic fields showed significantly better earthworm performance in improving the substrate's cultivability, including pH (closer to 7), available nutrients, humus content and wheat seedling rate. Microbial community analyses revealed more mechanisms: the higher earthworm-gut fungal Shannon index (α-diversity) under high-magnetic field verified the earthworm's impaired grinding/digesting function; for earthworm gut molecular ecological networks under stronger magnetic fields, the higher proportion of positive correlations suggests slower microbial cooperations (e.g., lignocellulose degradation task); the decreased Network Size, Average Path Length and Modularity indicated a substantial disruption of microbial interactions. This study disproves the stressful role of lunar (or space) low-magnetic field on the earthworm-lunar soil-waste system in BLSS, providing important reference for further deep-space BLSS research.