How will climate change effect the face of Wyoming's rangeland ecosystems over the next 100 years? To find out, Elise Pendall, associate professor of ecosystem ecology, has taken her research underground.
Pendall is part of an international team studying the effects of increased heat, moisture, and atmospheric carbon dioxide (CO2) on Wyoming's grasslands. Now in its sixth year, the Prairie Heating and CO2 Enrichment (or PHACE) experiment is one of only a handful of field-based climate change simulations taking place worldwide. It's one of the first such experiments involving rangeland, a sensitive biome that occupies over 250 million hectares in the United States. PHACE's collaborators include the U.S. Department of Agriculture and universities in North America, Europe, and Australia.
While much climate change research examines atmospheric and surface processes, Pendall focuses on the carbon, nutrient, and water cycling happening below ground. In fact, she's been studying the relationship between soil processes and climate change since the 1990s. "When I was a graduate student, there was an experiment similar to this one, one of the first I participated in," she says. "I realized that soils were playing a big role in the ecosystem response because of the feedback between carbon cycling and climate change."
The PHACE site consists of 30 circular prairie plots at the USDA's High Plains Grasslands Research Station near Cheyenne. All plots are equipped with heating units and a ring-shaped device that dispenses CO2. To simulate Wyoming's climate around the year 2100, researchers raise ambient temperatures a few degrees Celsius and increase atmospheric CO2 concentrations by about 50 percent.
Pendall's soil work has special implications for farmers and ranchers. "As climate change progresses, the forage quality—in other words, the nutritional quality of the plants the cattle are eating—is going to change," she says. Her findings highlight just how complex climate-soil interactions can be. For example, plants grown in laboratories under enriched CO2 conditions are often deficient in nitrogen, a key building block of protein for grazing animals. But Pendall finds that warmer soils produce nitrogen-rich plants—offsetting much of the nitrogen loss caused by CO2.
Pendall's research, which is supported by grants from the National Science Foundation and the National Institute of Food and Agriculture, will also be used to improve existing climate change models. Early modelers warned that increased temperatures might stimulate decomposition of organic soil matter, causing soils to release more CO2 into the air. This influx of CO2 would further accelerate warming and decomposition, eventually creating a self-reinforcing feedback loop that could destabilize the global climate system.
However, preliminary findings by Pendall and colleagues suggest that modelers need to consider additional factors. "Warming by itself dries out the soil enough that decomposition is suppressed, and there's less CO2 coming out," Pendall explains. "Information like that isn't currently embedded in models. We need more experiments like those so modelers can predict future climate change."
Flush with a new grant from the Department of Energy, Pendall expects to be busy with PHACE through 2013. And how does a soil ecologist spend her meager free time? "I definitely love gardening," she says. "But I can't do it as much as I'd like."