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Nitrates as a Potential N Supply for Microbial Ecosystems in a Hyperarid Mars Analog System

School of Earth and Environmental Sciences and Centre for Exoplanet Science, University of St Andrews, St Andrews KY16 9AL, Scotland, UK
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Received: 24 July 2019 / Revised: 8 October 2019 / Accepted: 17 October 2019 / Published: 19 October 2019
(This article belongs to the Special Issue Selected Papers from 8th Astrobiology Society of Britain Conference)
Nitrate is common in Mars sediments owing to long-term atmospheric photolysis, oxidation, and potentially, impact shock heating. The Atacama Desert in Chile, which is the driest region on Earth and rich in nitrate deposits, is used as a Mars analog in this study to explore the potential effects of high nitrate levels on growth of extremophilic ecosystems. Seven study sites sampled across an aridity gradient in the Atacama Desert were categorized into 3 clusters—hyperarid, middle, and arid sites—as defined by essential soil physical and chemical properties. Intriguingly, the distribution of nitrate concentrations in the shallow subsurface suggests that the buildup of nitrate is not solely controlled by precipitation. Correlations of nitrate with SiO2/Al2O3 and grain sizes suggest that sedimentation rates may also be important in controlling nitrate distribution. At arid sites receiving more than 10 mm/yr precipitation, rainfall shows a stronger impact on biomass than nitrate does. However, high nitrate to organic carbon ratios are generally beneficial to N assimilation, as evidenced both by soil geochemistry and enriched culturing experiments. This study suggests that even in the absence of precipitation, nitrate levels on a more recent, hyperarid Mars could be sufficiently high to benefit potentially extant Martian microorganisms. View Full-Text
Keywords: nitrate; Mars; Atacama Desert; sedimentation rates; biomass preservation; extremophiles nitrate; Mars; Atacama Desert; sedimentation rates; biomass preservation; extremophiles
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Shen, J.; Zerkle, A.L.; Stueeken, E.; Claire, M.W. Nitrates as a Potential N Supply for Microbial Ecosystems in a Hyperarid Mars Analog System. Life 2019, 9, 79.

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