Texas Tech University

Biology Researchers Studying Climate Change's Effect on Plants and Soil Microbes in Antarctica

Glenys Young

January 22, 2019

Natasja van Gestel is investigating the growth of moss on land that, until recently, was covered in ice.

Texas Tech University has a long history of academic research in Antarctica. In the 1960s, geology researchers led by Alton Wade studied Antarctic rocks to answer what was then an open question: how did the world look millions of years ago?

Midnight sun

The newest Texas Tech research in Antarctica is not about our planet's history, however. It's about its future.

Natasja van Gestel, an assistant professor in the Texas Tech Department of Biological Sciences, is spending four months at the bottom of the world to study how climate change affects plant and microbial life there.

If you thought there were no plants in Antarctica, you thought wrong.

Or rather, you thought 50 years ago.


True, less than 1 percent of land in Antarctica is ice-free, but that percentage is growing. The area van Gestel is studying was covered by a glacier in the 1960s, but that glacier has retreated about 500 meters since then, thanks to the continually warming climate felt most keenly in Antarctica. As the glacier has retreated, it has left open new land for plants to grow.

Natasja van Gestel and Kelly McMillen hike in an ice-free area near the Palmer Research Station.

"We thus have a great chronosequence where distance from the glacier relates to plant cover," van Gestel said. "Nearly 90 percent of the 244 glaciers on the Antarctic Peninsula have retreated since the 1950s and continue to do so. The chronosequence thus gives us an idea how other areas where glaciers are receding will respond to warming in terms of microbial and plant responses."

Along with graduate student Kelly McMillen, van Gestel is studying the entire gradient of exposed ground, from sites with no visible vegetation, to sites completely covered in plants.

Flourishing mosses
Polytrichum, left, and Chorisodontium are two of the mosses flourishing in Antarctica.

"There are about 100 species of moss and only two vascular plant species: Antarctic hairgrass and Pearlwort," van Gestel said. "My highest plant productivity site is on nearby Litchfield Island, an Antarctic Specially Protected Area, which requires a special permit to enter. My lowest plant productivity site is only a few meters from the glacier's edge. Although there are no visible plants there, there are microbes in the soil that are photosynthesizing. These microbes are important contributors to carbon fluxes."

The research

Those carbon fluxes – changes in the rates of respiration and photosynthesis as the plant and microbial populations change – are a vital part of van Gestel's research, which will study both the plant productivity gradient and how warming conditions affect different organisms differently.

Measuring carbon
Natasja van Gestel and Kelly McMillen measure initial soil carbon levels before beginning their warming experiment.

"We expect carbon fluxes to increase with increases in plant cover – that is, with increasing distance from the glacier," van Gestel said. "We expect that the number of microbes will increase along the gradient and that their activities will be higher with increases in plant cover. Likewise, we expect to find that the active microbial communities will change along the gradient, in part because, close to the glacier, conditions for microbes may be harder: nutrients are likely to be very limiting and the temperatures would be cooler on average.

"We also expect there will be quite a few kinds of microbes that may not be active at all: they may have blown in from elsewhere and are now stuck in frigid Antarctica with conditions too extreme for them to operate in. We might also find microbes that are not active near the glacier's edge but would be active under different circumstances, for example, if there was more vegetation – so perhaps they're biding their time."

The soil sisters
Natasja van Gestel, left, poses with Alicia Purcell, center, and Kelly McMillen. To other Antarctic researchers, the three are known as "the Soil Sisters."

And while the current gradient conditions are certainly important to study for the long-term insights they provide, just as important will be the findings from van Gestel's warming experiment to show just how quickly changes are happening. Alicia Purcell, a doctoral student at Northern Arizona University, will use a technique called quantitative stable isotope probing (qSIP), a novel method developed by van Gestel's collaborator Bruce Hungate, director of the Center of Ecosystem Science and Society at Northern Arizona University, to identify what microorganisms are actively growing and how fast.

Using open-top warming chambers that allow in sunlight and trap its heat, van Gestel and McMillen can warm small areas of soil and vegetation while still allowing precipitation – this means variables other than temperature are kept as consistent as possible so they're only testing the effects of the temperature.

Warming chambers
Open-top warming chambers are seen in an area of light moss cover.

Van Gestel's research team collects four intact soil/moss core samples from each of four research sites spread across the plant productivity gradient, then add water to the cores and replace them within the warming chamber for at least two weeks. One pair of cores receives highly purified water, while the other pair receives water containing a heavier oxygen isotope, oxygen-18.

"Microbes that are active will use water," van Gestel said. "The heavier oxygen from the water is incorporated into their DNA and thus makes their DNA heavier. We can calculate growth rates from how much heavier their DNA becomes. Those that have become much heavier are those that grew the fastest. Those that do not show any differences in DNA density are those that did not grow.

"The field qSIP technique with intact cores has never been used in Antarctica before, and we believe it will provide a novel understanding of microbes. We will use the data on microbial growth rates and on photosynthetic activity of plants to understand controls of ecosystem carbon balance. So getting data from both plants and microbes is essential."

Oxygen-18 is added to soil.
Soil from a site with no visible plants receives its treatment with the heavier oxygen isotope, oxygen-18.

The idea, ultimately, is to study how climate change is affecting organisms in Antarctica and how these changes ultimately affect ecosystem carbon balance. A big worry in the scientific community is whether warming reduces how much carbon the land takes up. Less carbon taken up by the land means more remains in the atmosphere in the form of CO2, and therefore, the rate of climate change may increase.

"Warmer conditions likely will benefit some organisms but not others; this could be true for plants, but also for microbes," van Gestel said. "Hence, we likely will expect a shift in microbial communities. It will be harder to find a shift in plant communities because the plants are very slow growing – for this we would need to monitor plant cover over a period of several years.

"What we do expect to find, though, is that carbon fluxes will be greater in the warmed plots relative to control plots. Carbon fluxes are sensitive to warming: photosynthesis and respiration rates increase in response to warming. What we do not know is how the net carbon flux – the difference in photosynthesis and respiration – will change in response to warming."

The effects

Because Antarctic plant and soil ecosystems are so much simpler than other ecosystems on Earth, van Gestel says the insights gathered there can give more information about the mechanisms of carbon storage and thus contribute to future climate models.

Flourishing plant life
Natasja van Gestel and Kelly McMillen pose in an area with lots of visible plant life.

"For example, is the efficiency by which microbes use carbon sensitive to temperature? Some of the carbon microbes consume is used to build biomass, but the remainder is lost through respiration," she said. "So, the question is: Will warmer temperatures make microbes more wasteful with carbon? This so-called microbial carbon use efficiency is an important parameter in models. In other ecosystems there are many confounding factors, and this question of temperature sensitivity is highly relevant. Why? Because if microbes become more wasteful, then greater respiratory losses would move more carbon from the soil to the atmosphere. If so, then warming results in more warming.

"Also, the warming rates of this region of Antarctica have already affected precipitation patterns: snowfall has increased, and more snow negatively impacts one of the true Antarctic penguin species, the Adélie penguin. More snow means wetter conditions following snowmelt, thereby causing penguin eggs to be submerged or chicks to drown. Higher snowfall with climate change in areas that naturally receive snow can be explained because warmer air can hold more moisture. More snow does not mean it is colder. So, what is happening on the Peninsula regarding higher snowfall with climate change is happening elsewhere, also. For example, snowstorms have increased in the northeastern United States."

Decreased sea ice
Kelly McMillen observes gentoo penguins. The shortage of sea ice is apparent.

The effects of climate change in Antarctica, van Gestel said, are obvious.

"One just has to look at how much the Antarctic landscape itself has changed in the last 30 years or so," she said. "The sea-ice season is on average about three months shorter than it was in the late 1970s. This is huge! Life here depends on the sea ice.

"Some species, initially rarely found, are now thriving because of warmer temperatures. Populations of true Antarctic species are in rapid decline whereas those that are more sub-Antarctic are increasing in numbers dramatically. This area of Antarctica is no longer what it used to be."

Seal and penguin
A gentoo penguin swims while a leopard seal lounges on an ice floe. Leopard seals are currently one of the top predators in Antarctic waters, which are too cold for sharks. There are concerns, however, that warming trends could change that.

However, those looking for evidence of climate change don't have to go to Antarctica to see it, she said.

"I worry, as a scientist, that there are still skeptics out there," van Gestel said. "One just has to look at the evidence of changes in climate everywhere, and not just in Antarctica. The evidence is all around us: for example, longer growing seasons for plants or more severe insect outbreaks because of milder winters. Sure, climate has changed in the past and will continue to change, but we have vastly accelerated the pace of change. This is not part of a natural cycle.

"If 97 percent of engineers tell you the building you are about to enter will collapse, would you trust the 3 percent who say it will not collapse and enter the building? Now substitute climate scientists for engineers. If we do not do something now, the consequences will be dire."

Follow van Gestel's blog to see the latest updates from her work in Antarctica.