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Azua-Bustos A, Fairén AG, Silva CG, Carrizo D, Fernández-Martínez MÁ, Arenas-Fajardo C, Fernández-Sampedro M, Gil-Lozano C, Sánchez-García L, Ascaso C, Wierzchos J, Rampe EB. Inhabited subsurface wet smectites in the hyperarid core of the Atacama Desert as an analog for the search for life on Mars. Sci Rep 2020; 10:19183. [PMID: 33154541 PMCID: PMC7645800 DOI: 10.1038/s41598-020-76302-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Accepted: 10/16/2020] [Indexed: 01/21/2023] Open
Abstract
The modern Martian surface is unlikely to be habitable due to its extreme aridity among other environmental factors. This is the reason why the hyperarid core of the Atacama Desert has been studied as an analog for the habitability of Mars for more than 50 years. Here we report a layer enriched in smectites located just 30 cm below the surface of the hyperarid core of the Atacama. We discovered the clay-rich layer to be wet (a phenomenon never observed before in this region), keeping a high and constant relative humidity of 78% (aw 0.780), and completely isolated from the changing and extremely dry subaerial conditions characteristic of the Atacama. The smectite-rich layer is inhabited by at least 30 halophilic species of metabolically active bacteria and archaea, unveiling a previously unreported habitat for microbial life under the surface of the driest place on Earth. The discovery of a diverse microbial community in smectite-rich subsurface layers in the hyperarid core of the Atacama, and the collection of biosignatures we have identified within the clays, suggest that similar shallow clay deposits on Mars may contain biosignatures easily reachable by current rovers and landers.
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Affiliation(s)
- Armando Azua-Bustos
- Centro de Astrobiología (CSIC-INTA), 28850, Madrid, Spain.
- Instituto de Ciencias Biomédicas, Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Santiago, Chile.
| | - Alberto G Fairén
- Centro de Astrobiología (CSIC-INTA), 28850, Madrid, Spain.
- Department of Astronomy, Cornell University, Ithaca, NY, 14853, USA.
| | | | - Daniel Carrizo
- Centro de Astrobiología (CSIC-INTA), 28850, Madrid, Spain
| | | | | | | | - Carolina Gil-Lozano
- Centro de Astrobiología (CSIC-INTA), 28850, Madrid, Spain
- Laboratory of Planetology and Geodynamics, Université de Nantes, 44322, Nantes, France
| | | | - Carmen Ascaso
- Museo Nacional de Ciencias Naturales (CSIC), 28006, Madrid, Spain
| | - Jacek Wierzchos
- Museo Nacional de Ciencias Naturales (CSIC), 28006, Madrid, Spain
| | - Elizabeth B Rampe
- Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX, USA
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2
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Shen J, Zerkle AL, Stueeken E, Claire MW. Nitrates as a Potential N Supply for Microbial Ecosystems in a Hyperarid Mars Analog System. Life (Basel) 2019; 9:life9040079. [PMID: 31635024 PMCID: PMC6958444 DOI: 10.3390/life9040079] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Revised: 10/08/2019] [Accepted: 10/17/2019] [Indexed: 11/16/2022] Open
Abstract
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.
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Affiliation(s)
- Jianxun Shen
- School of Earth and Environmental Sciences and Centre for Exoplanet Science, University of St Andrews, St Andrews KY16 9AL, Scotland, UK.
| | - Aubrey L Zerkle
- School of Earth and Environmental Sciences and Centre for Exoplanet Science, University of St Andrews, St Andrews KY16 9AL, Scotland, UK.
| | - Eva Stueeken
- School of Earth and Environmental Sciences and Centre for Exoplanet Science, University of St Andrews, St Andrews KY16 9AL, Scotland, UK.
| | - Mark W Claire
- 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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3
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Powers LS, Smith HD, Kilungo AP, Ellis WR, McKay CP, Bonaccorsi R, Roveda JW. In situ real-time quantification of microbial communities: Applications to cold and dry volcanic habitats. Glob Ecol Conserv 2018. [DOI: 10.1016/j.gecco.2018.e00458] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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4
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Wilhelm MB, Davila AF, Parenteau MN, Jahnke LL, Abate M, Cooper G, Kelly ET, Parro García V, Villadangos MG, Blanco Y, Glass B, Wray JJ, Eigenbrode JL, Summons RE, Warren-Rhodes K. Constraints on the Metabolic Activity of Microorganisms in Atacama Surface Soils Inferred from Refractory Biomarkers: Implications for Martian Habitability and Biomarker Detection. ASTROBIOLOGY 2018; 18:955-966. [PMID: 30035640 DOI: 10.1089/ast.2017.1705] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Dryness is one of the main environmental challenges to microbial survival. Understanding the threshold of microbial tolerance to extreme dryness is relevant to better constrain the environmental limits of life on Earth and critically evaluate long-term habitability models of Mars. Biomolecular proxies for microbial adaptation and growth were measured in Mars-like hyperarid surface soils in the Atacama Desert that experience only a few millimeters of precipitation per decade, and in biologically active soils a few hundred kilometers away that experience two- to fivefold more precipitation. Diversity and abundance of lipids and other biomolecules decreased with increasing dryness. Cyclopropane fatty acids (CFAs), which are indicative of adaptive response to environmental stress and growth in bacteria, were only detected in the wetter surface soils. The ratio of trans to cis isomers of an unsaturated fatty acid, another bacterial stress indicator, decreased with increasingly dry conditions. Aspartic acid racemization ratios increased from 0.01 in the wetter soils to 0.1 in the driest soils, which is indicative of racemization rates comparable to de novo biosynthesis over long timescales (∼10,000 years). The content and integrity of stress proteins profiled by immunoassays were additional indicators that biomass in the driest soils is not recycled at significant levels. Together, our results point to minimal or no in situ microbial growth in the driest surface soils of the Atacama, and any metabolic activity is likely to be basal for cellular repair and maintenance only. Our data add to a growing body of evidence that the driest Atacama surface soils represent a threshold for long-term habitability (i.e., growth and reproduction). These results place constraints on the potential for extant life on the surface of Mars, which is 100-1000 times drier than the driest regions in the Atacama. Key Words: Atacama Desert-Dryness-Growth-Habitability-Biomarker-Mars. Astrobiology 18, 955-966.
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Affiliation(s)
- Mary Beth Wilhelm
- 1 School of Earth and Atmospheric Sciences, Georgia Institute of Technology , Atlanta, Georgia
- 2 Space Science and Astrobiology Division, NASA Ames Research Center , Moffett Field, California
| | - Alfonso F Davila
- 2 Space Science and Astrobiology Division, NASA Ames Research Center , Moffett Field, California
| | - Mary N Parenteau
- 2 Space Science and Astrobiology Division, NASA Ames Research Center , Moffett Field, California
| | - Linda L Jahnke
- 2 Space Science and Astrobiology Division, NASA Ames Research Center , Moffett Field, California
| | - Mastewal Abate
- 2 Space Science and Astrobiology Division, NASA Ames Research Center , Moffett Field, California
| | - George Cooper
- 2 Space Science and Astrobiology Division, NASA Ames Research Center , Moffett Field, California
| | | | - Victor Parro García
- 4 Departamento Evolución Molecular, Centro de Astrobiologia (INTA-CSIC) , Madrid, Spain
| | - Miriam G Villadangos
- 4 Departamento Evolución Molecular, Centro de Astrobiologia (INTA-CSIC) , Madrid, Spain
| | - Yolanda Blanco
- 4 Departamento Evolución Molecular, Centro de Astrobiologia (INTA-CSIC) , Madrid, Spain
| | - Brian Glass
- 5 Intelligent Systems Division, NASA Ames Research Center , Moffett Field, California
| | - James J Wray
- 1 School of Earth and Atmospheric Sciences, Georgia Institute of Technology , Atlanta, Georgia
| | - Jennifer L Eigenbrode
- 6 Planetary Environments Laboratory, NASA Goddard Space Flight Center , Greenbelt, Maryland
| | - Roger E Summons
- 7 Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology , Cambridge, Massachusetts
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5
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Namib Desert primary productivity is driven by cryptic microbial community N-fixation. Sci Rep 2018; 8:6921. [PMID: 29720684 PMCID: PMC5932006 DOI: 10.1038/s41598-018-25078-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2017] [Accepted: 04/09/2018] [Indexed: 12/03/2022] Open
Abstract
Carbon exchange in drylands is typically low, but during significant rainfall events (wet anomalies) drylands act as a C sink. During these anomalies the limitation on C uptake switches from water to nitrogen. In the Namib Desert of southern Africa, the N inventory in soil organic matter available for mineralisation is insufficient to support the observed increase in primary productivity. The C4 grasses that flourish after rainfall events are not capable of N fixation, and so there is no clear mechanism for adequate N fixation in dryland ecosystems to support rapid C uptake. Here we demonstrate that N fixation by photoautotrophic hypolithic communities forms the basis for the N budget for plant productivity events in the Namib Desert. Stable N isotope (δ15N) values of Namib Desert hypolithic biomass, and surface and subsurface soils were measured over 3 years across dune and gravel plain biotopes. Hypoliths showed significantly higher biomass and lower δ15N values than soil organic matter. The δ15N values of hypoliths approach the theoretical values for nitrogen fixation. Our results are strongly indicative that hypolithic communities are the foundation of productivity after rain events in the Namib Desert and are likely to play similar roles in other arid environments.
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Wilhelm MB, Davila AF, Eigenbrode JL, Parenteau MN, Jahnke LL, Liu XL, Summons RE, Wray JJ, Stamos BN, O’Reilly SS, Williams A. Xeropreservation of functionalized lipid biomarkers in hyperarid soils in the Atacama Desert. ORGANIC GEOCHEMISTRY 2017; 103:97-104. [PMID: 29743757 PMCID: PMC5937136 DOI: 10.1016/j.orggeochem.2016.10.015] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Our understanding of long-term organic matter preservation comes mostly from studies in aquatic systems. In contrast, taphonomic processes in extremely dry environments are relatively understudied and are poorly understood. We investigated the accumulation and preservation of lipid biomarkers in hyperarid soils in the Yungay region of the Atacama Desert. Lipids from seven soil horizons in a 2.5 m vertical profile were extracted and analyzed using GC-MS and LC-MS. Diagnostic functionalized lipids and geolipids were detected and increased in abundance and diversity with depth. Deeper clay units contain fossil organic matter (radiocarbon dead) that has been protected from rainwater since the onset of hyperaridity. We show that these clay units contain lipids in an excellent state of structural preservation with functional groups and unsaturated bonds in carbon chains. This indicates that minimal degradation of lipids has occurred in these soils since the time of their deposition between >40,000 and 2 million years ago. The exceptional structural preservation of biomarkers is likely due to the long-term hyperaridity that has minimized microbial and enzymatic activity, a taphonomic process we term xeropreservation (i.e. preservation by drying). The degree of biomarker preservation allowed us to reconstruct major changes in ecology in the Yungay region that reflect a shift in hydrological regime from wet to dry since the early Quaternary. Our results suggest that hyperarid environments, which comprise 7.5% of the continental landmass, could represent a rich and relatively unexplored source of paleobiological information on Earth.
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Affiliation(s)
- Mary Beth Wilhelm
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332 USA
- Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, CA 94035 USA
- Corresponding author: Telephone: (650) 604-0489;
| | - Alfonso F. Davila
- Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, CA 94035 USA
- SETI Institute 189 N Bernardo Ave, Mountain View, CA 94043 USA
| | - Jennifer L. Eigenbrode
- Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 USA
| | - Mary N. Parenteau
- Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, CA 94035 USA
| | - Linda L. Jahnke
- Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, CA 94035 USA
| | - Xiao-Lei Liu
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02141 USA
| | - Roger E. Summons
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02141 USA
| | - James J. Wray
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332 USA
| | - Brian N. Stamos
- Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas 76019 USA
| | - Shane S. O’Reilly
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02141 USA
| | - Amy Williams
- Department of Physics, Astronomy, and Geosciences, Towson University, 8000 York Road, Towson, MD 21252 USA
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Abstract
The evolution of habitable conditions on Mars is often tied to the existence of aquatic habitats and largely constrained to the first billion years of the planet. Here, we propose an alternate, lasting evolutionary trajectory that assumes the colonization of land habitats before the end of the Hesperian period (ca. 3 billion years ago) at a pace similar to life on Earth. Based on the ecological adaptations to increasing dryness observed in dryland ecosystems on Earth, we reconstruct the most likely sequence of events leading to a late extinction of land communities on Mars. We propose a trend of ecological change with increasing dryness from widespread edaphic communities to localized lithic communities and finally to communities exclusively found in hygroscopic substrates, reflecting the need for organisms to maximize access to atmospheric sources of water. If our thought process is correct, it implies the possibility of life on Mars until relatively recent times, perhaps even the present.
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Affiliation(s)
- Alfonso F Davila
- 1 Carl Sagan Center at the SETI Institute , Mountain View, California, USA
- 2 NASA Ames Research Center , Moffett Field, California, USA
| | - Dirk Schulze-Makuch
- 3 School of the Environment, Washington State University , Pullman, Washington, USA
- 4 Center of Astronomy and Astrophysics, Technical University Berlin , Berlin, Germany
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8
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Davila AF, Hawes I, Araya JG, Gelsinger DR, DiRuggiero J, Ascaso C, Osano A, Wierzchos J. In situ metabolism in halite endolithic microbial communities of the hyperarid Atacama Desert. Front Microbiol 2015; 6:1035. [PMID: 26500612 PMCID: PMC4594028 DOI: 10.3389/fmicb.2015.01035] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 09/11/2015] [Indexed: 01/01/2023] Open
Abstract
The Atacama Desert of northern Chile is one of the driest regions on Earth, with areas that exclude plants and where soils have extremely low microbial biomass. However, in the driest parts of the desert there are microorganisms that colonize the interior of halite nodules in fossil continental evaporites, where they are sustained by condensation of atmospheric water triggered by the salt substrate. Using a combination of in situ observations of variable chlorophyll fluorescence and controlled laboratory experiments, we show that this endolithic community is capable of carbon fixation both through oxygenic photosynthesis and potentially ammonia oxidation. We also present evidence that photosynthetic activity is finely tuned to moisture availability and solar insolation and can be sustained for days, and perhaps longer, after a wetting event. This is the first demonstration of in situ active metabolism in the hyperarid core of the Atacama Desert, and it provides the basis for proposing a self-contained, endolithic community that relies exclusively on non-rainfall sources of water. Our results contribute to an increasing body of evidence that even in hyperarid environments active metabolism, adaptation, and growth can occur in highly specialized microhabitats.
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Affiliation(s)
| | - Ian Hawes
- Gateway Antarctica, University of Canterbury , Christchurch, New Zealand
| | - Jonathan G Araya
- Laboratorio de Microorganismos Extremófilos, Instituto Antofagasta, Universidad de Antofagasta , Antofagasta, Chile
| | - Diego R Gelsinger
- Department of Biology, Johns Hopkins University , Baltimore, MD, USA
| | | | - Carmen Ascaso
- Grupo de Ecología y Geomicrobiología del Sustrato Lítico, Departamento de Biogeoquímica y Ecología Microbiana, Museo Nacional de Ciencias Naturales (MNCN), Consejo Superior de Investigaciones Científicas (CSIC) , Madrid, Spain
| | - Anne Osano
- Department of Natural Sciences, Bowie State University , Bowie, MD, USA
| | - Jacek Wierzchos
- Grupo de Ecología y Geomicrobiología del Sustrato Lítico, Departamento de Biogeoquímica y Ecología Microbiana, Museo Nacional de Ciencias Naturales (MNCN), Consejo Superior de Investigaciones Científicas (CSIC) , Madrid, Spain
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9
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Life at the hyperarid margin: novel bacterial diversity in arid soils of the Atacama Desert, Chile. Extremophiles 2012; 16:553-66. [DOI: 10.1007/s00792-012-0454-z] [Citation(s) in RCA: 125] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 04/02/2012] [Indexed: 10/28/2022]
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Austin AT. Has water limited our imagination for aridland biogeochemistry? Trends Ecol Evol 2011; 26:229-35. [PMID: 21397975 DOI: 10.1016/j.tree.2011.02.003] [Citation(s) in RCA: 121] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 02/08/2011] [Accepted: 02/09/2011] [Indexed: 10/18/2022]
Abstract
The classic ecological paradigm for deserts, that all processes are controlled by water availability, has limited our imagination for exploring other controls on the cycling of carbon and nutrients in aridland ecosystems. This review of recent studies identifies alternative mechanisms that challenge the idea that all soil processes in aridlands are proximately water-limited, and highlights the significance of photodegradation of aboveground litter and the overriding importance of spatial heterogeneity as a modulator of biotic responses to water availability. Aridlands currently occupy >30% of the terrestrial land surface and are expanding. It is therefore critical to incorporate these previously unappreciated mechanisms in our understanding of aridland biogeochemistry to mitigate the effects of desertification and global change.
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Affiliation(s)
- Amy T Austin
- Instituto de Investigaciones Ecológicas y Fisiológicas Vinculadas a la Agricultura (IFEVA-CONICET), Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453 Buenos Aires, (C1417DSE) Argentina.
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Fairén AG, Davila AF, Lim D, Bramall N, Bonaccorsi R, Zavaleta J, Uceda ER, Stoker C, Wierzchos J, Dohm JM, Amils R, Andersen D, McKay CP. Astrobiology through the ages of Mars: the study of terrestrial analogues to understand the habitability of Mars. ASTROBIOLOGY 2010; 10:821-843. [PMID: 21087162 DOI: 10.1089/ast.2009.0440] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Mars has undergone three main climatic stages throughout its geological history, beginning with a water-rich epoch, followed by a cold and semi-arid era, and transitioning into present-day arid and very cold desert conditions. These global climatic eras also represent three different stages of planetary habitability: an early, potentially habitable stage when the basic requisites for life as we know it were present (liquid water and energy); an intermediate extreme stage, when liquid solutions became scarce or very challenging for life; and the most recent stage during which conditions on the surface have been largely uninhabitable, except perhaps in some isolated niches. Our understanding of the evolution of Mars is now sufficient to assign specific terrestrial environments to each of these periods. Through the study of Mars terrestrial analogues, we have assessed and constrained the habitability conditions for each of these stages, the geochemistry of the surface, and the likelihood for the preservation of organic and inorganic biosignatures. The study of these analog environments provides important information to better understand past and current mission results as well as to support the design and selection of instruments and the planning for future exploratory missions to Mars.
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Austin AT, Araujo PI, Leva PE. Interaction of position, litter type, and water pulses on decomposition of grasses from the semiarid Patagonian steppe. Ecology 2009; 90:2642-7. [PMID: 19769141 DOI: 10.1890/08-1804.1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Litter lignin and nutrient content, annual rainfall, and biotic activity are not good predictors of litter decomposition in arid and semiarid ecosystems, suggesting that other factors may be important in controlling carbon turnover. We explored the relative importance of litter position (above- vs. belowground), litter type (leaf vs. root), and pulsed water events (large vs. small) on mass loss with grass species of the semiarid Patagonian steppe. In a factorial experiment of mesocosms, we incubated leaf and root litter simultaneously above- and belowground and manipulated water availability with large and small pulses. Significant interactions between position and litter type and position and pulse sizes demonstrated interactive controls on organic mass loss. Aboveground decomposition showed no response to pulse size or litter type, as roots and leaves decomposed equally rapidly under all circumstances. In contrast, belowground decomposition was significantly altered by litter type and water pulses, with roots decomposing significantly slower and small water pulses reducing belowground decomposition. The results of this mesocosm experiment support the idea that controls other than water availability may dominate aboveground mass loss, while a combination of recalcitrant litter and water penetration in the soil profile are critical factors determining belowground decomposition, which is ultimately mediated by biotic degradation.
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Affiliation(s)
- Amy T Austin
- Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura and Consejo Nacional de Investigaciones Científicas y Tecnicas, Facultad de Agronomia, Universidad de Buenos Aires, Av. San Martin 4453, Buenos Aires (C1417DSE) Argentina.
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