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E I Friedmann

Publications and source records attributed to E I Friedmann.

At least 37 records · Page 2Linked to original sources
PubMed1988

The cryptoendolithic microbial environment in the Ross Desert of Antarctica: mathematical models of the thermal regime.

Microbial activity in the Antarctic cryptoendolithic habitat is regulated primarily by temperature. Previous field studies have provided some information on the thermal regime in this habitat, but this type of information is limited by the remoteness of the site and the harsh climatic conditions. Therefore, a mathematical model of the endolithic thermal regime was constructed to augment the field data. This model enabled the parameters affecting the horizontal and altitudinal distribution of the community to be examined. The model predicts that colonization should be possible on surfaces with zenith angle less than 15 degrees. At greater zenith angles, colonization should be restricted to surfaces with azimuth angles less than 135 degrees or greater than 225 degrees. The upper elevational limit of the community should be less than 2,500 m. The thermal regime probably does not influence the zonation of the community within a rock.

Algorithms↗
PubMed1988

The cryptoendolithic microbial environment in the Ross Desert of Antarctica: light in the photosynthetically active region.

The vertical zonation of the Antarctic cryptoendolithic community appears to form in response to the light regime in the habitat. However, because of the structure of the habitat, the light regime is difficult to study directly. Therefore, a mathematical model of the light regime was constructed, which was used to estimate the total photon flux in different zones of the community. Maximum fluxes range from about 150 micrometers photons m-2 s-1 at the upper boundary of the community to about 0.1 micrometer photons m-2 s-1. Estimates of the annual productivity in the community indicate that the lowest zone of the community is light limited, with the maximal annual carbon uptake equivalent to less than the carbon content of one algal (Hemichloris) cell.

Antarctic Regions↗
PubMed1988

The effect of low temperature on Antarctic endolithic green algae.

Laboratory experiments show that undercooling to about -5 degrees C occurs in colonized Beacon sandstones of the Ross Desert, Antarctica. High-frequency temperature oscillations between 5 degrees C and -5 degrees C or -10 degrees C (which occur in nature on the rock surface) did not damage Hemichloris antarctica. In a cryomicroscope, H. antarctica appeared to be undamaged after slow or rapid cooling to -50 degrees C. 14CO2 incorporation after freezing to -20 degrees C was unaffected in H. antarctica or in Trebouxia sp. but slightly depressed in Stichococcus sp. (isolated from a less extreme Antarctic habitat). These results suggest that the freezing regime in the Antarctic desert is not injurious to endolithic algae. It is likely that the freezing-point depression inside the rock makes available liquid water for metabolic activity at subzero temperatures. Freezing may occur more frequently on the rock surface and contribute to the abiotic nature of the surface.

Antarctic Regions↗
PubMed1988

Temperature response of Antarctic cryptoendolithic photosynthetic microorganisms.

Growth responses to temperatures between 12.5 [degrees] C and 25 degrees C were determined for five photosynthetic microorganisms isolated from the Ross Desert cryptoendolithic community. Among eukaryotic algae, two strains of Trebouxia sp. have an upper temperature limit of 20 degrees C, and two strains of Hemichloris antarctica of 25 degrees C. The cyanobacterium Chroococcidiopsis sp., in contrast, grows at temperatures above 25 degrees C. These and earlier studies suggest that the eukaryotic algae of the Antarctic cryptoendolithic community have an upper temperature limit near 25 degrees C.

Antarctic Regions↗
PubMed1988

Cryptoendolithic lichen and cyanobacterial communities of the Ross Desert, Antarctica.

Cryptoendolithic microbial communities in the Ross Desert (McMurdo Dry Valleys) are characterized on the basis of photosynthetic microorganisms and fungi. Two eukaryotic communities (the lichen-dominated and Hemichloris communities) and three cyanobacterial communities (the red Gloeocapsa, Hormathonema-Gloeocapsa, and Chroococcidiopsis communities) are described. Eleven coccoid, one pleurocapsoid, and five filamentous cyanobacteria occurring in these communities are characterized and illustrated. The moisture grade of the rock substrate seems to affect pH, formation of primary iron stain, and the distribution of microbial communities.

Antarctic Regions↗
PubMed1987

Microbial trace-fossil formation, biogenous, and abiotic weathering in the Antarctic cold desert.

In the Antarctic cold desert (Ross Desert), the survival of the cryptoendolithic microorganisms that colonize the near-surface layer of porous sandstone rocks depends on a precarious equilibrium of biological and geological factors. An unfavorable shift of this equilibrium results in death, and this may be followed by formation of trace fossils that preserve the characteristic iron-leaching pattern caused by microbial activity. Similar microbial trace fossil may exist in the geological record. If life ever arose on early Mars, similar processes may have occurred there and left recognizable traces.

Antarctic Regions↗
PubMed1987

The cryptoendolithic microbial environment in the Ross Desert of Antarctica: satellite-transmitted continuous nanoclimate data, 1984 to 1986.

A satellite mediated station for monitoring nanoclimate (climate in the millimeter range) data, suitable for use in polar regions is described. The station, located in the Ross desert of Antarctica, has been in operation for more than 3 years, measuring rock temperatures, air temperature, light, snow, wind, and moisture. The data indicate that biological activity in the cryptoendolithic microbial ecosystem is limited to the period from mid November to mid February. The total number of hours of biological activity, based on assumptions of the minimum light, temperature and moisture requirements of the community, is less than 1000 h/year. The time above 0 degrees C, representing more nearly optimal conditions, is between 50 and 550 h/year, depending on the orientation of the surface.

Antarctic Regions↗
PubMed1987

Control of matric water potential by temperature differential.

A method for controlling relative humidity based on temperature differentials, rather than on salt solutions, is described. This method has the following advantages: (1) it does not exhibit the anomalous CO2 solution effects that we have found to occur with salt solutions; (2) humidity is continuously adjustable without sample removal; (3) circulation of the atmosphere results in short equilibration times.

Atmosphere↗
PubMed1987

Heterococcus endolithicus sp. nov. (Xanthophyceae) and other terrestrial Heterococcus species from Antarctica: morphological changes during life history and response to temperature.

Strains of Heterococcus endolithicus sp. nov., H. pleurococcoides Pitschmann, H. caespitosus Vischer, and H. protonematoides Vischer isolated from terrestrial habitats in Antarctica were studied in culture. Morphology of the algae changes with stage in life history. The characteristic branching patterns are not present in very young or old cultures. Filament formation is suppressed when cultures are grown outside their optimal temperature range.

Antarctic Regions↗
PubMed1987

Antarctic cryptoendolithic microbial ecosystem research, 1986-1987

The apparent lifelessness of the Ross Desert is in marked contrast to the diversity of cryptoendolithic microorganisms inhabiting the interstices of sandstone rocks. The endolithic habitat provides a protective niche for lichens, bacteria, algae, and fungi, enabling them to exist in an extremely dry and cold climate. Composed solely of microorganisms living under the surface of rocks and totally lacking animals and protozoa, this ecosystem is controlled by measurable physical variables and well suited for ecosystem study and modeling. The work of the antarctic cryptoendolithic microbial ecosystem research group has involved physical measurements of nanoclimate (microbial environment inside rocks) (Friedmann, McKay, and Nienow 1987), taxonomy (Darling, Friedmann, and Broady 1987; Hale 1987), microdistribution, organism-substrate interactions including the ongoing process of fossilization (Friedmann and Weed 1987), physiological ecology, and quantification of the nitrogen economy.

Antarctic Regions↗
PubMed1986

The Antarctic cold desert and the search for traces of life on Mars.

The cryptoendolithic microorganisms that live inside rocks in the frigid Ross Desert of Antarctica can serve as a terrestrial model for what may have happened to life forms on Mars when the planet became dry and cold. Trace fossils of microbial rock colonization exist in Antarctica, and similar structures could have formed on Mars. In some respects, such trace fossils could be an easier target for life-detection systems than fossils of cellular structures.

Adaptation, Biological↗
PubMed1985

The cryptoendolithic microbial environment in the Antarctic cold desert: temperature variations in nature.

In the Antarctic cold desert, cryptoendolithic microorganisms live under the surface of porous sandstone rocks. During the austral summer, the environment of the near-surface rock layers colonized by organisms is characterized by two kinds of temperature oscillations, both occurring across the freezing point. Low-frequency (diurnal) and large-amplitude (up to about 20 degrees C) oscillations on the sunlit surface of rocks result in a daily freeze-thaw cycle. This is a result of the diurnal changes in the sun altitude and angle with respect to the rock surface. The biological effect of this oscillation is the regulation of the onset and cessation of metabolic activity. The high-frequency (few minutes) oscillations occur only under certain weather conditions (sunny days with light winds) and are superimposed on the low-frequency oscillations. They are caused by the cooling effect of wind gusts on rock surfaces that are much warmer than ambient air temperatures. High-frequency oscillations result in a rapid freeze-thaw cycle on the surface, which, however, does not reach the microbial zone. These high-frequency freeze-thaw oscillations are probably the cause of the abiotic nature of the rock surface. Both oscillations seem to have an effect on rock weathering.

Air↗
PubMed1984

The Antarctic cryptoendolithic ecosystem: relevance to exobiology.

Cryptoendolithic microorganisms in the Antarctic desert live inside porous sandstone rocks, protected by a thin rock crust. While the rock surface is abiotic, the microclimate inside the rock is comparatively mild. These organisms may have descended from early, pre-glaciation Antarctic life forms and thus may represent the last outpost of life in a gradually deteriorating environment. Assuming that life once arose on Mars, it is conceivable that, following the loss of water, the last of surviving organisms withdrew to similar insulated microenvironments. Because such microscopic pockets have little connection with the outside environment, their detection may be difficult. The chances that the Viking lander could sample cryptoendolithic microorganisms in the Antarctic desert would be infinitesimal.

Arctic Regions↗
PubMed1984

Hemichloris antarctica, gen. et sp. nov. (Chlorococcales, Chlorophyta), a cryptoendolithic alga from Antarctica.

Hemichloris antarctica gen. et sp. nov. (Oocystaceae, Chlorococcales) is characterized by a single, articulated, pyrenoid-less, thick saucer-shaped chloroplast, which generally fills less than half of the cell periphery. Multiplication is only by autospores. The species is psychrophilic and is damaged at temperatures above 20 degree C. Hemichloris antarctica is a member of the cryptoendolithic microbial community living in porous sandstone rocks of the Antarctica cold desert. It inhabits the zone below that of cryptoendolithic lichens and survives at extremely low light intensities. In the natural habitat, morphology is somewhat different from that in culture, as chloroplasts are smaller and without articulation, and the cells develop a gelatinous sheath.

Antarctic Regions↗