Microbial response to deliquescence of nitrate-rich soils in the hyperarid Atacama Desert

Abstract. Life in hyperarid regions has adapted to extreme water scarcity by using salt deliquescence. 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 regarding water availability and biogeochemistry. Microbial abundances and composition were determined by cell cultivation experiments and 16S rRNA gene sequencing while microbial activity was assessed by analyzing ATP, PLFA, and the molecular composition of organic matter. Our findings reveal that while the studied hygroscopic salts provide temporary water, microbial abundances, and activities are lower than in non-deliquescent soil surfaces. Intriguingly, the deliquescent crusts are enriched in geochemically degraded organic matter. 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.