An experiment in a dry Antarctic stream channelhas shown that a carpet of freeze-dried microbes that lay dormant fortwo decades sprang to life one day after water was diverted into it,said a University of Colorado at Boulder researcher.
The results showed the resilience of life in the harsh polarenvironment, where temperatures are below freezing for most of the yearand glacial melt water flows for only five to 12 weeks annually, saidProfessor Diane McKnight of CU-Boulder's Institute of Arctic and AlpineResearch. Such research on life in extreme environments is of highinterest to astrobiologists, who consider Antarctica's McMurdo DryValleys an analogue for Mars because of its inhospitable climate andintermittent water flow.
"This was something we did not anticipate," said McKnight,whose research group is working at Antarctica's McMurdo Dry ValleysLong Term Ecological Research, or LTER, site funded by the NationalScience Foundation. "These mats not only persisted for years when therewas no water in the streambed, but blossomed into an entire ecosystemin about a week. All we did was add water."
McKnight gave a presentation on the experiment at theEcological Society of America's 90th Annual Meeting held Aug. 7 to Aug.12 in Montreal.
The river channels under study feature intermittent streamsthat link glaciers to frozen lakes on the valley floor, she said. Thestreambeds contain photosynthetic microbes known as cyanobacteria,which collectively occur as thin, rubbery mat-like structures that canspread several meters across the streambed surface.
The experiment began in the 1994 research season, when theteam used sandbags to divert water from an active streambed in theMcMurdo Dry Valleys into the dry streambed, she said. A time series ofaerial photographs, coupled with carbon isotope analyses of thecyanobacteria that measured variation in atmospheric carbon overdecades, indicated the streambed had been dry for about 20 years.
"After we diverted the water into the channel, photosynthesisbegan the same day and the mats became abundant within a week," shesaid. "This showed us that they had been preserved in a cryptobioticstate."
Over the next several years, the microbial mats in theexperimental channel had higher growth rates than mats in adjacentstreambeds receiving annual summer water flow, she said. The studyshowed the new microbial mats were taking up atmospheric nitrogen at ahigher rate than mats in adjacent streambeds, increasing biomassproductivity, she said. As photosynthetic bacteria, cyanobacteria arebelieved by biologists to be among the first living organisms tocolonize Earth. The mats generally are orange or black and consist of10 to 15 different species of cyanobacteria, she said.
Because of a cooling trend in the McMurdo Dry Valleys, somestreambeds that normally have annual summer flows have been dry inrecent years, McKnight said. In contrast, the Antarctic Peninsula haswarmed nearly 5 degrees Fahrenheit in the past 60 years and has seenthe collapse of several major ice shelves and significant glacialthinning in recent years, according to several international studies.
The McMurdo Dry Valleys region consists of glaciers, openexpanses of barren ground, stream channels and permanently ice-coveredlakes. The life forms inhabiting the area include microorganisms,mosses, lichens and a few groups of invertebrates.
Study collaborators included Cathy Tate of the U.S.Geological Survey, Denver; Ned Andrews of the USGS, Boulder, Colo.; DevNiyogi of the University of Missouri-Rolla; CU-Boulder graduate studentKaren Cozetto; Cathy Welsh and Berry Lyons of Ohio State University;and Douglas Capone of the University of California, Irvine.
The McMurdo Dry Valleys site is one of 26 LTER sites in theworld designated by NSF. Approximately 25 scientists participate inresearch during each field season.
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