New observatory to probe the mysteries of Earth’s ‘forgotten’ subsoil | Science

Just a meter or two down, below the topsoil that nurtures crops, is a little known part of the ecosystem that may be critical to the planet’s climate future. But this deep soil is surprisingly hard to study. It helps to know the right backhoe operator, and even then extracting samples without disturbing their structure or inhabitants is tricky. “The deeper you go, the harder it is,” says Daniel Richter, a soil scientist at Duke University.

Last month, the U.S. National Science Foundation announced funding for a new $19 million research facility, called the Deep Soil Ecotron, that aims to make studying this frontier easier. The initial design for the lab, to be built over the next 5 years at the University of Idaho, calls for 24 richly instrumented soil columns topped with airtight chambers for vegetation. These ecosystems-in-a-lab, or ecounits, will allow researchers to manipulate environmental conditions down to 3 meters. Surprises are assured. “It’s kind of like when people launched the first deep-sea submarine,” says Zachary Kayler, a co–principal investigator (co-PI) and biogeochemist at the University of Idaho. “The possibilities are endless.”

Ultimately, researchers hope to use the ecotron facility to study a wide range of questions, including how the deep soil might release carbon and accelerate climate change, how soil microbes and plants interact, and how torrential summer rains and hard winter freezes influence the birth and growth of soil. The center could also become a testbed for new sensors that reveal what’s happening in deep soil in the real world. Planners hope to attract researchers from across the United States and host multiple experiments at once. “This facility has potential that’s incredibly exciting,” says Sharon Billings, an ecosystem scientist at the University of Kansas, Lawrence.

About a dozen ecotron facilities exist, nearly all in Europe. But they allow researchers to tinker with just one or two soil conditions, usually precipitation. In contrast, the new U.S. lab will allow researchers to manipulate a host of factors throughout the entire columns, including temperature, moisture, and carbon dioxide concentrations (which influence rock weathering and soil formation). They will be able to simulate the upwelling of groundwater and perhaps even the freeze-thaw cycles that can speed soil development.

The ecotron also opens the door to studying deep life, including invertebrates, says Nico Eisenhauer, an ecologist at the German Centre for Integrative Biodiversity Research who advises the U.S. ecotron. Little is known about the activity of these organisms, he says, but their hidden behavior could be monitored in the new ecounits. Acoustic sensors, for instance, can track earthworm activity, whereas buried tubes with small entrances collect and count tiny invertebrates that stumble in.

Researchers who study soil carbon note that topsoil—typically the first 30 centimeters—has been well studied because it is crucial for agriculture. Scientists have assumed this shallow, root- and microbe-rich layer holds most soil carbon. But a few studies of the deeper, vaster subsoils suggest they might contain at least as much carbon, some of it carried down by roots. “It’s the forgotten half of soil organic carbon,” says soil biogeochemist Michael Schmidt of the University of Zurich.

Studying how that carbon responds to climate change is a key goal for the ecotron, which can simulate changing conditions “with a degree of control I’ve never seen before,” says Emma Aronson, a soil scientist at the University of California, Riverside. Deep soils are expected to warm as Earth heats up, and field experiments suggest that could cause soil to release carbon into the atmosphere 30% to 50% faster than today, accelerating global warming. Precipitation shifts caused by climate change will also have an impact. For example, wetting of desert soils, especially those that have been polluted with reactive nitrogen can lead to much greater emissions of nitrous oxide, a potent greenhouse gas.

Idaho is “really a cool place” to locate the ecotron lab because it boasts a diverse range of soils, says the project’s PI, microbial ecologist Michael Strickland of the University of Idaho. He and colleagues are still mulling how many and which types of soils to place into the columns. “Capturing dynamics in different types of soils will be key,” says soil biogeochemist Asmeret Asefaw Berhe, who is awaiting Senate confirmation to lead the Department of Energy’s Office of Science.

One challenge will be extracting and moving the selected soils. Field crews must disturb them as little as possible, Richter says, because their structure influences the movement of gases, water, and particles. Strickland hopes new equipment from the company building the facility will be able to extract long cores intact. But no matter how tender the touch, researchers expect the samples to have severed roots and surfaces that will be exposed to oxygen for the first time in centuries or millennia. It could take years for the extracted soil to return to equilibrium, says Pete Smith, a soil scientist at the University of Aberdeen.

Despite the unknowns, excitement is already building among soil scientists. “The fun will really start,” says co-PI Rodrigo Vargas, an ecosystem ecologist at the University of Delaware, Newark, “once it’s built.”

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