By Catherine Doss, College of Science
For more than a decade, Jeb Barrett, assistant professor of biological sciences, has been uncovering surprises in his quest to determine how long-term climate trends affect ecological processes.
Some people might consider the first surprise to be the setting: Antarctica, the coldest place on Earth. Barrett is part of a group of scientists from nine universities who conduct research under the auspices of the Long-term Ecological Research Network, a National Science Foundation program that sponsors multidisciplinary studies of the ecosystems in an ice-free region of Antarctica. Barrett and his colleagues, who are physical scientists, biologists, and ecologists, work in the McMurdo Dry Valleys in the eastern region of the Antarctic. To many people, association of the word "dry" with Antarctica may seem to be a misfit.
"Most people envision Antarctica as a great big sheet of ice," Barrett says. "But the dry valleys are ice-free. They consist of a cold, desert-like terrain located in a mountain chain that is high enough to block the movement of ice sheets."
Life in the Valleys
The dry valleys are so named because of the exceedingly low humidity there. The region is considered one of the world's most extreme deserts.
'Antarctica is the only place on Earth that is still as it should be. May we never tame it.' – Andrew Denton
From this rugged vantage point, Barrett is examining what controls the distribution of microorganisms in these frigid conditions. The forms of life he studies are primitive: mostly bacteria, fungi, and roundworms. Through soil samples and DNA testing, he studies the spatial distribution of these organisms, focusing on such questions as: Are these life forms universally distributed? Or are they distinct populations that are the result of local evolutionary processes?
Only a fraction of the microorganisms Barrett comes across can be cultured. Therefore, DNA kits are used to help replicate and increase small amounts of biological material so that it can be more easily studied.
"We're looking at what distinguishes the distribution of microorganisms at very fine spatial scales ranging from centimeters to meters," he says. "While climate change is the ultimate context in how we do the work, we're also trying to determine how systems work under natural conditions."
Scientists conduct this type of research in Antarctica because of its pristine conditions. The continent is virtually undisturbed by humans, which means the research isn't affected by roads, cars, people, and other means for an organism to move from one environment to another. Soil there can be as old as 5 million years. It's a chiseled, barren landscape.
Variety: The Spice of Life
Surprise number two: the diversity of species within individual communities.
'You can see the biology in the frozen ponds.' – Jeb Barrett
"We found bacterial diversity as high as what you would find in tropical rain forests," Barrett says. "This diversity allows us to look at the effects of climate change on individual species and in turn look at how the removal of certain species or the movement of species will influence ecological processes. Basically, what controls the limits to the distribution of life?"
In some cases, organisms are endemic to a certain community. Such is the case with the nematode Scottnema lindsayae, which appears nowhere else on Earth. One of the adaptations of endemic organisms is that some are able to become inactive during inhospitable climate conditions and become active again when the climate is favorable.
"We were puzzled when we found bacterial diversity high," Barrett says. "What we expect is that a lot of these are inactive organisms."
For some invertebrates, while the species may be endemic to a certain area, their families are more universally distributed. These organisms are the ones found in wet areas adjacent to glacier melts, streams, or lakes.
"Our current work is to determine not only the spatial distribution of communities, but how much of what we find in the soils is actually a 'freeze-dried' reserve," Barrett says. "One idea is that the organisms present in the reserve might provide some sort of stability or resilience to climate variation. That's how our questions of distribution are related to the ultimate questions of climate change."
Because these organisms are microscopic, Barrett's team uses molecular techniques to study how they function in the environment. Genetic observation is easier and more effective than trying to measure a change in a slow-moving ecosystem function, such as carbon or nitrogen cycling.
In another region of the continent, south of Australia and New Zealand, dry valleys are glacially carved in the Transarctic Mountains. One limit to the distribution of life in this region is the poor soil quality, most of which consists of debris left behind by glaciers. This coarse sand substance is low in organic content and high in salt, neither of which is conducive to the distribution of life.
'This region of Antarctica is probably one of the most extreme environments ... and one of the most poorly studied.' – Jeb Barrett
The Long-term Ecological Research Network (LTER) group, comprised of 1,800 biologists and physical scientists, among others, studies ecological processes over a diverse set of sites and ecosystems in the United States and two sites in the Antarctic. By its interdisciplinary nature, the group is able to take a comprehensive snapshot of how species respond to a number of environmental variables. The McMurdo Dry Valleys LTER site serves as a sentinel of change in an extreme polar environment. Virginia Tech's involvement in Antarctic research began in the 1970s with projects led by George Simmons and Bruce Parker, professors emeritus of biological sciences.
"This region of Antarctica is probably one of the most extreme environments in terms of water and nutrients and one of the most poorly studied," Barrett says. "Only within the last decade have people started to look at the microbiology in the soils. In fact, some of these environments were described as 'sterile' as recently as the 1970s."
By isolating organisms from the soil, the research group hopes to start identifying which genes in the microorganisms are actually functioning; i.e., which ones are alive and responding to environmental changes.
In a recent project, Barrett and his group traveled to Beardmore Glacier to gather samples of some of the most southern exposed soil on Earth. Building upon previous knowledge from Barrett's work in the McMurdo Dry Valleys, members were able to make inferences for a wide latitudinal transect. The group is studying whether the same organisms are in the soil across that wide geographic range.
"The processes that occur that allow you to have high diversity in such an extreme environment mean either that we're simply observing dead cells or that the organisms have reserves in the soil that act as a seed bank," he says. "Determining what's in the reservoir may give us some sense of how these systems may respond to climate change over time."
In addition, Barrett noted that currently, there is no consistent climate trend in the region due to seasonal holes in the ozone layer of the atmosphere that can cause rapid and fluctuating changes in temperature. By learning what the impact is on ecosystems at the local level, Barrett hopes to get a better understanding of the effects of global climate changes.
An early surprise in his research occurred in 2002 when Barrett, working in the dry valley, witnessed a dramatic change in temperatures. Within a period of two weeks, the environment he was working in went from a paradigm of cooling, not much water, and very inactive biology to two weeks of record warming and glacier melt.
"In those two weeks, lake levels came back up to the levels they had been 10 years earlier," Barrett says. "It really indicated to me how sensitive these environments are. Marginal, sustained warming over that short period of time caused a fundamental switch in the ecosystem."
Intellectually, Barrett knew the system should be capable of responding like that, similar to a sudden bloom of desert wildflowers after it rains. "But seeing it and actually being out there when it was happening was very different."
Barrett says what he is learning in the harsh world of Antarctica can be applied to more temperate environments.
"My research looks at what the impacts on ecological processes are now," he says. "It's one thing to talk about climate changes over the next 50 to 60 years, but the Antarctic is an environment where we can measure impacts quickly.
On a fundamental level, it helps us understand what the controls over the distribution of life are."