Soil Systems as Astrobiological Models: Microbial Communities, Environmental Stressors, and Planetary Analogues

Soils are complex, heterogeneous systems that link terrestrial ecology and astrobiology. Microbial persistence in these systems reflects not only intrinsic cellular resistance but also interactions among organisms, mineral components, organic matter, and spatially structured microhabitats. These characteristics make soil systems valuable experimental models for investigating microbial survival and biosignature preservation under extraterrestrial-relevant conditions. However, most studies of microbial tolerance to planetary and space-related stressors have focused on pure cultures, providing limited insight into natural communities. This review synthesizes evidence on the tolerance of soil- and rock-associated microorganisms to combined environmental constraints, including radiation, vacuum and low pressure, low water availability, perchlorates, and impact-related stresses. Particular attention is given to differences between isolated microorganisms and natural communities and to how microbial interactions, biofilms, spatial organization, and mineral matrices may modify persistence. Evidence from laboratory simulations, stratospheric exposures, and orbital experiments indicates that microbial persistence and biosignature preservation can differ between natural community/native-matrix systems and simplified experimental systems. Integrating multifactorial laboratory experiments with stratospheric and orbital exposures of natural microbial communities should improve assessments of microbial persistence under planetary conditions. Such integration should also advance understanding of soil-mediated controls on biosignature preservation and interpretation of potential extraterrestrial habitats.