HR: 1330h
AN: B52B-1042    [PDF]
TI: Exploring the Limits to Photosynthetic Life in the Hyperarid Atacama (Chile) and Taklimakan (China) Deserts
AU: * Warren-Rhodes, K
EM: kwarren-rhodes@mail.arc.nasa.gov
AF: NASA-Ames Research Center, Planetary Sciences Branch Mail Stop 245-3, Moffett Field, CA 94035 United States
AU: Ewing, S
EM: saewing@nature.berkeley.edu
AF: University of California at Berkeley, Division of Ecosystem Science Department of Environmental Science, Policy and Management, Berkeley, CA 94720 United States
AU: McKay, C P
EM: cmckay@mail.arc.nasa.gov
AF: NASA-Ames Research Center, Planetary Sciences Branch Mail Stop 245-3, Moffett Field, CA 94035 United States
AU: Rhodes, K L
EM: KLRHODES_GROUPER@YAHOO.COM
AF: Pacific Marine Science and Conservation, 160 Conaway, Grass Valley, CA 95945 United States
AB: Photosynthetic microbes inhabiting the cracks or fissures (chasmoendoliths) and undersides (hypoliths) of translucent stones function as the sole primary producers in the world's driest deserts. This poster reports on our studies of the distribution and survival of these microorganisms in the hyperarid core of the Atacama Desert--an extreme environment previously considered too dry to support photosynthetic life--and the Taklimakan Desert in China--one of the oldest and driest deserts on the Earth. In both deserts, we measured colonization rates and microclimate variables across natural precipitation gradients in order to investigate the role of moisture in the ecology and survival of hypolithic and chasmoendolithic microorganisms. Our results show 1000-fold variations in colonization rates--from 12% in the wettest portions of the Taklimakan Desert to $<$1% in the arid core of the Atacama--that correspond at the macro-scale to decreased mean annual precipitation (MAP) of $\sim$45mm to $\sim$ 0mm. In the Atacama, soil $\Delta$$^{14}$C signatures suggest slow but active organic carbon cycling by hypolithic communities. In the hyperarid core of the Atacama, the $\Delta$$^{14}$C signature of organic carbon in hypolith-colonized soils beneath translucent stones was -276 $\permil$, corresponding to a steady state turnover time of $>$3000 y. At slightly wetter sites in the Atacama, $\Delta$$^{14}$C of hypolith soils was progressively more enriched in proportion to increased MAP, with corresponding turnover times of $>$600 y ($\Delta$$^{14}$C = -73 $\permil$ at sites with $\sim$5-10 mm MAP and $\sim$1 y $\Delta$$^{14}$C = +12 $\permil$) as annual rainfall increased to $\sim$25 mm. At all sites, $\Delta$$^{14}$C signatures of non-hypolith soils corresponded to turnover times that were longer by an order of magnitude, indicating significantly slower OC cycling by non-hypoliths. In the hyperarid core of the Atacama Desert, the prolonged lack of rainfall (decadal scales of a few millimeters) is responsible for possibly the lowest hypolithic and chasmoendolithic colonization rates observed in deserts on the Earth. Microclimate data for rock and soil surface moisture from rainfall, dew and frost suggest the particular form of moisture and its frequency may also explain observed differences in hypolithic versus chasmoendolithic colonization modes. These results hold theoretical and practical considerations for both terrestrial ecology and as analogs for possible life on Mars.
DE: 6225 Mars
SC: Biogeosciences [B]
MN: 2003 Fall Meeting