Image: Tianshan Mountain Range
This aerial view shows a hyper-arid desert near the Tianshan Mountain Range in northwest China, where the scientists surveyed for microbial life.
By Staff Writer
updated 4/3/2007 4:51:38 PM ET 2007-04-03T20:51:38

Results from a recent study of the microbes in China’s remote deserts could help astrobiologists refine their maps for uncovering Martian life.

Ongoing studies of Mars analogs on Earth have combed the iciest regions and the driest areas. But the new study, published in the Feb. 15 issue of the Journal of Geophysical Research-Biogeosciences, is the first comprehensive look at the microbial life in the extreme deserts of China.

“If you go to the Dry Valleys in Antarctica, that is arguably the coldest place on Earth, and certain areas in the Atacama Desert are some of the driest on Earth,” said lead author Kimberley Warren-Rhodes of NASA Ames Research Center.

“What we didn’t have, and which is more similar to Mars, is a combination of those conditions,” she added, until now.

Harsh life
Warren-Rhodes and her colleagues, including her advisor Chris McKay of NASA Ames, examined the abundance and diversity of blue-green algae called cyanobacteria in several spots in the extreme deserts of China.

They chose three locations based on temperatures and amount of rainfall. One site, called Tokesun, was warm and dry and located about 500 feet (152 meters) below sea level, making it the lowest point in China. Another site, called Ruoqiang, runs parallel to the southern edge of the Taklimakan Desert and is hot and wet.

The last site, Sorkuli, is situated along the Qinghai-Tibetan plateau and lies between 8,200 feet and 9,840 feet (2,500 meters to 3,000 meters) above sea level. This high-altitude desert included two climates: cold and dry, and cold and wet.

Like green plants, cyanobacteria capture the sun’s energy to carry out photosynthesis and turn inorganic ingredients into organic material needed for growth. On Earth, water is the limiting factor for carrying out photosynthesis, and this would be particularly true on the parched planet of Mars. But ecologists suspect that microbes can live within rock pores or beneath translucent rocks where moisture is most likely to remain, possibly on both planets.

So the team also used data recorders at the Chinese sites to measure “micro-climate” conditions, including the relative humidity, moisture, temperature and light levels in the soil, beneath rocks and within pore spaces of rocks.

An increase in rainfall was typically associated with a spike in microbial density, but there were other factors too. “Rainfall amounts primarily dictated the type of microbial ecosystems we found across sites, but the effects of temperature, humidity and light created a gradient of soil water conditions suitable for life as well,” McKay said.

Microbial hideouts
The microbes preferred some tiny homes more than others, the scientists found. “When you start talking about microbiology in a planetary sense, we work at these larger scales, but it’s this microclimate scale that’s really important to these organisms,” Warren-Rhodes said.

“We’re finding that there are certain characteristics that make it more probable to find [microbial life] than not in these really harsh deserts,” Warren-Rhodes said. One feature is rock size, with the larger rocks supporting higher densities of cyanobacteria, presumably because they can store more water.

“We look at these rocks, and these are small, just tens of centimeters. But to [microbes], that’s like living on a huge mountain range,” Warren-Rhodes told “Think of the variations from the top to the bottom of a mountain range and that’s what’s important to these microbes.”

She added, “So we have to get into that perspective to understand the conditions that make one habitat super-accommodating and one centimeter next door not so much.”

Once life takes hold in a hostile environment, it could change its home-base to make it more conducive for survival. “Many of these organisms exude certain types of material that may act as sponges in their environment,” Warren-Rhodes said. The sticky substances are known as extracellular slime. "When [the substances] get wet, they swell to several times their original volume and may serve as a reservoir for water in extremely dry deserts," Warren-Rhodes explained.

The scientists plan next to study the spatial distribution of microbes, along with the associated climate features, in the Atacama Desert and in Antarctica.

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