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Abstract:
Life in hyperarid regions has adapted to extreme
water scarcity through mechanisms like salt deliquescence.
While halite (NaCl) crusts have been intensively studied
and identified as one of the last habitats under hyperarid
conditions, other less common hygroscopic salt crusts remain
unexplored. Here, we investigated newly discovered
deliquescent soil surfaces in the Atacama Desert, containing
substantial amounts of nitrates, to evaluate their habitability
for microorganisms. We characterized the environment
with respect to water availability and biogeochemistry.
Microbial abundances and composition were determined
by cell cultivation experiments, 16S rRNA gene sequencing,
and membrane phospholipid fatty acid (PLFA)
analysis, while microbial activity was assessed by analyzing
adenosine triphosphate (ATP) and the molecular composition
of organic matter. Our findings reveal that, while the
studied hygroscopic salts provide temporary water, microbial
abundances and activity are lower in the studied soil surfaces
than in non-deliquescent soil surfaces. Intriguingly, the
deliquescent crusts are enriched in geochemically degraded
organic matter, indicated by the molecular composition. We
conclude that high nitrate concentrations in the hyperarid
soils suppress microbial activity but preserve eolian-derived
biomolecules. These insights are important for assessing the
habitability and searching for life in hyperarid environments
on Earth and beyond.
