Abstract

Human endeavours into deep space exploration and the prospects of establishing colonies on nearby planets would invariably involve components of bioregenerative life support for food production, cabin atmosphere renewal, and waste recycling. Growing plants and their microbiomes in porous media under different gravitational fields may present new challenges due to effects of liquid distribution on gaseous exchange with roots and microorganisms. We provide the first direct evidence that capillary driven liquid reconfiguration in porous media under reduced gravity conditions reduces oxygen diffusion pathways and enhances anoxic conditions within bacterial hotspots. Parabolic flight experiments using model porous media inoculated with aerobic and facultative anaerobic bacteria reveal the systematic enhancement of anoxic conditions during the reduced gravity periods in the presence but not in the absence of bacterial activity. The promotion of anoxic conditions under reduced gravity may lead to higher nitrous oxide and methane emissions relative to Earth conditions, on the other hand, anoxic conditions could be beneficial for perchlorate bioremediation of Martian soil. The results highlight changes in soil bacterial microhabitats under reduced gravity and the challenges of managing bioregenerative life support systems in space.

Highlights

  • Human endeavours into deep space exploration and the prospects of establishing colonies on nearby planets would invariably involve components of bioregenerative life support for food production, cabin atmosphere renewal, and waste recycling

  • We provide direct evidence that bacteria contribute to the creation of anoxic hotspots in unsaturated porous media in reduced gravity, and that this effect is due to the homogenized distribution of the aqueous phase that results in the blocking of previously gas-filled pores

  • Experiments were performed as part of the 3rd Swiss Parabolic Flight campaign, which consisted of two flights and a total of 32 parabolas (14 zero-gravity parabolas, one Lunar gravity and one Martian gravity parabola per flight)

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Summary

Introduction

Human endeavours into deep space exploration and the prospects of establishing colonies on nearby planets would invariably involve components of bioregenerative life support for food production, cabin atmosphere renewal, and waste recycling Growing plants and their microbiomes in porous media under different gravitational fields may present new challenges due to effects of liquid distribution on gaseous exchange with roots and microorganisms. Due to the approximately thousand-fold lower diffusivity of gases in water relative to air, a more homogeneous distribution of the aqueous phase poses a barrier to gaseous diffusion within the porous matrix[13] This creates conditions that can favor local anoxic hotspots due to root and microbial respiration, with profound consequences for plant and microbial activity and the functioning of the BRLSS. We observed a consistent decrease in oxygen content in bacteria-loaded pore networks compared to sterile pore networks, with the magnitude of the effect varying with the strength of the gravitational acceleration

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