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Oak Ridge National Laboratory Researchers of Plants, Roots, and Soil Shed Light on Arctic Ecosystem

 

Polygon formations in Alaska provide researchers with a unique natural laboratory with which to study the Arctic and, by extension, the Earth’s climate. Image credit: NGEE-ArcticPolygon formations in Alaska provide researchers with a unique natural laboratory with which to study the Arctic and, by extension, the Earth’s climate. Image credit: NGEE-Arctic (hi-res image)

This feature describes Oak Ridge National Laboratory research presented at the 98th annual meeting of the Ecological Society of America. The theme of the meeting, held Aug. 4-9 in Minnesota, is "Sustainable Pathways: Learning From the Past and Shaping the Future."

Despite the enormity of climate research in the past couple of decades, one area in particular still poses major questions.

The Arctic is a vast, complex ecosystem that covers a large portion of the Earth’s surface and plays a critical role in global climate processes. Yet we know remarkably little about it, particularly its plants.

To gain a better understanding of the importance of Arctic vegetation in climate models, a team of researchers from Oak Ridge National Laboratory’s Climate Change Science Institute is taking a closer look at the intricacies of the Arctic’s plant communities, research that has huge implications for global climate models. Because plants are instrumental in the terrestrial carbon, water and energy exchange, the team’s work will not only reveal much about the Earth’s northern latitudes but also help climate modelers in their quest to better understand the complex relationships that, woven together, create Earth’s climate. They shared their work Aug. 5 in Minnesota during talks at the annual meeting of the Ecological Society of America.

Using the environs of Barrow, Alaska, as their laboratory, ORNL researchers Stan Wullschleger, Richard Norby, Colleen Iversen, Joanne Childs and Victoria Sloan study different portions of the Arctic plant ecosystem that, while seemingly separate, are all intricately connected. They are participants in the Next-Generation Ecosystem Experiments (NGEE-Arctic) project of the U.S. Department of Energy’s Office of Science. NGEE-Arctic seeks to increase confidence in climate projections by quantifying the physical, chemical and biological behavior of terrestrial ecosystems in Alaska. The results will likely inform research in the greater Arctic, which is warming twice as fast as the rest of the planet.

If climate models are to continue to evolve, a better understanding of the Arctic is necessary. The NGEE-Arctic project will entail three years of integrated modeling and experiment at the Barrow Experimental Observatory followed by a decade of extending the approach across Alaska. Data will be used to reduce uncertainty in climate models and help predict the effects of global warming over the next century.

Plants of a feather

Even with the most powerful computers in the world, climate scientists are forced to make numerous approximations and classifications to simplify their models. For example, plant functional types, or PFTs, are categories researchers use to classify plants according to certain characteristics, i.e., deciduous versus evergreen trees, or trees versus grasses. Scientists need a database of where the various categories are located on the globe. Enter Stan Wullschleger, who is attempting to better classify Arctic plants by type and function, giving climate modelers one more level of precision in their quest to better predict the years ahead.

Despite this need, the Community Land Model, a portion of the popular Community Earth System Model used to model global climate change, treats all of the Arctic’s diverse plant types as a “grass.” A better, more precise classification system is needed to further our understanding of the larger Arctic ecosystem and its effects on the Earth’s climate.

“The challenge likely to be encountered in moving forward with modeling vegetation dynamics lies in evaluating the trade-offs between simplicity in our classification of PFTs, while capturing sufficient complexity in describing differences among PFTs for major ecosystem properties and processes,” said Wullschleger.

If climate models are to continue to increase in accuracy, a more nuanced and thorough classification of PFTs is critical.

After the thaw

Wullschleger’s teammate, Richard Norby, is digging a little deeper, literally. By exploring the effects of soil nitrogen on the Arctic’s vegetation, Norby is gaining a better understanding of the role of climate change in reorganizing plant communities. It’s expected among researchers that as climate change escalates, the Arctic’s thawing permafrost will release nitrogen stored in the soil for eons.

The released nitrogen will almost certainly escalate plant growth, but different plant types will respond differently. “Essentially, we’re linking plant community structure and function to soil moisture and nutrient availability,” said Norby. By studying the relationship between leaf area and nitrogen availability in polygonal land structures around Barrow, Norby hopes to make accurate estimates of the effects of nitrogen on Arctic plant life.

Specifically, Norby’s project tracks nitrogen availability with depth as the active permafrost layer thaws during the growing season; seasonal variation in plant nitrogen; the spectral signatures of plant communities that will correlate with nitrogen content; and the linkage between plant and soil characteristics, with root characteristics controlling nitrogen uptake.

Norby soon hopes to expand his research to other sites in Alaska that are undergoing rapid change.

“A reorganization of Arctic plant communities may be a significant result of climate change that drives important feedbacks to the atmosphere and to permafrost stability,” he said.

The root of it all

More may be happening just under that permafrost than we know. The final piece in the team’s research involves the classification of root systems. Just as Wullschleger is attempting a finer categorization of plant types and function, his colleague Colleen Iversen hopes to accomplish the same with the Arctic’s root systems.

Surprisingly, belowground plant characteristics are not represented in most large-scale climate models. And in environments such as the tundra that are typified by extreme conditions, surveys indicate that roots and belowground stems can contain as much as six times the mass of aboveground plant parts. The plant species that call the tundra home have a variety of unique adaptations that enable them to survive in harsh Arctic conditions. These unique, integral systems are begging to be classified and, ultimately, associated with PFTs for a more complete representation in models of the processes that govern the Arctic ecosystem.

The symbiotic nature of the team’s various research interests all serve one purpose: to give climate modelers a better picture of the Arctic, a heretofore mysterious region that is not accurately represented in modern models yet plays critical roles in the global climate system. Therefore, scale is at the heart of the research.

“When I measure roots in the soil, I’m measuring in centimeters,” said Iversen. “Ultimately, I want to be able to scale that to 100 meters.”

Despite being tucked away in a little corner of Northern Alaska, the team’s research has truly global implications. Simply put, a more accurate model of the Arctic equals a more accurate model of the world.

 -  Gregory Scott Jones,  865.574.6944,  August 08, 2013
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