Hypolithic Cyanobacteria, Dry Limit of Photosynthesis, and Microbial Ecology in the Hyperarid Atacama Desert
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Kimberley A. Warren-Rhodes [3] ; Kevin L. Rhodes [1] ; Stephen B. Pointing [4] ; Stephanie A. Ewing [5] ; Donnabella C. Lacap [4] ; Benito Gómez-Silva [2] ; Ronald Amundson [5] ; E. Imre Friedmann [3] ; Christopher P. McKay [3]
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[1] University of Hawaii at Hilo
University of Hawaii at Hilo
Estados Unidos
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[2] Universidad de Antofagasta
Universidad de Antofagasta
Antofagasta, Chile
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[3] NASA-Ames Research Center. USA
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[4] Department of Ecology and Biodiversity, University of Hong Kong. China
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[5] Department of Environmental Science, Policy and Management, Ecosystem Sciences Division, University of California at Berkeley. USA
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- Localización: Microbial ecology, ISSN-e 1432-184X, ISSN 0095-3628, Vol. 52, Nº. 3, 2006, págs. 389-398
- Idioma: inglés
- Texto completo no disponible (Saber más ...)
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Resumen
The occurrence of hypolithic cyanobacteria colonizing translucent stones was quantified along the aridity gradient in the Atacama Desert in Chile, from less arid areas to the hyperarid core where photosynthetic life and thus primary production reach their limits. As mean rainfall declines from 21 to ≤2 mm year−1, the abundance of hypolithic cyanobacteria drops from 28 to <0.1%, molecular diversity declines threefold, and organic carbon residence times increase by three orders of magnitude. Communities contained a single Chroococcidiopsis morphospecies with heterotrophic associates, yet molecular analysis revealed that each stone supported a number of unique 16S rRNA gene-defined genotypes. A fivefold increase in steady-state residence times for organic carbon within communities in the hyperarid core (3200 years turnover time) indicates a significant decline in biological carbon cycling. Six years of microclimate data suggest that the dry limit corresponds to ≤5 mm year−1 rainfall and/or decadal periods of no rain, with <75 h year−1 of liquid water available to cyanobacteria under light conditions suitable for photosynthesis. In the hyperarid core, hypolithic cyanobacteria are rare and exist in small spatially isolated islands amidst a microbially depauperate bare soil. These findings suggest that photosynthetic life is extremely unlikely on the present-day surface of Mars, but may have existed in the past. If so, such microhabitats would probably be widely dispersed, difficult to detect, and millimeters away from virtually lifeless surroundings.
