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UA's Biosphere 2 experimenting with how rainforests deal with drought

In the high desert near Oracle, Ariz. a half-acre rainforest will become the stage for a four-month-long experiment to try and understand how rainforests respond to drought. 

The study is the Water, Atmosphere and Life Dynamics, or WALD experiment, a reference to the German word for "forest." Hosted at the University of Arizona's Biosphere 2, an international research team is studying how the forest, including microbes in its soil, respond to the potential stress of a hotter, drier climate. 

In the meantime, Biosphere 2 has closed its rainforest section to the public for the duration of the experiment, a move that harkens back to the first days of the center near Tucson, allowing researchers to tease out very subtle measurements in volatile organic compounds—substances that are in shampoos and perfumes, and substances that plants and microbes may use to communicate. 

"We’re broadly curious about an ecosystem’s response to drought, and we’re measuring it in a way that’s unparalleled," said Laura Meredith, the rainforest science director for Biosphere 2 and one of three leads on the project. "We get to control when the drought happens, and we’re ready with instruments. This is helpful for testing models to predict what happens with global tropical forests under climate change." 

"It perfectly aligns with B2's mission," said John Adams, deputy director at Biosphere 2. "The mesocosms, or model ecoystems, have been functioning for 34 years since the original experiments, and these systems are complex, and they've reached a stabilization point. So, doing things like this experiment, when we're drying down the rainforest we're able to understand how a drought changes this system." 

"It's a really interesting experiment, and this is virtually impossible to do anywhere else," Adams said. "It's not that the Biosphere 2's rainforest is a direct analog, but it gives us a highly-controlled component, and that helps us understand the mechanisms that tie together the soil, plant and atmospheric interactions. And, then we can have a higher confidence about what happens," he said. 

The analysis is part of a larger $2.1 million, five-year project funded by a grant from the European Research Council, given to Christiane Werner, a professor of ecosystem physiology at Germany’s University of Freiburg, and one of the project leads. Junior investigator Nemiah Ladd, also of Freiburg, co-organized the grant and is the third project lead.

Packed into a glass-walled ziggurat about 130 feet on a side and nearly 100 feet tall, the Biosphere 2 rainforest normally receives about 5,300 gallons of rainfall—enough to fill more than 65 bathtubs—three times per week. Through September, Meredith and the team will take measurements and observe the biome under normal conditions, relying on a suite of sensors that have been trucked in for this purpose to track how carbon dioxide and water vapor flow through the system before and after the drought, allowing the team to better understand how the rainforest responds to stress, Werner told UA News. 

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"The first part is to go to individual components of the ecosystem, such as the leaves, soil and roots, and understand how they process carbon," said Meredith. "When plants have carbon in the bank, they need to decide how to spend it under stress." 

"We specifically want to do this at Biosphere 2 because we get this extra level of control, we can create a drought, and we're really well-poised to measure it," Meredith said. Bringing this many instruments into a regular rainforest is too complex, and researchers can't simple create and relieve a drought, "when we want to," she said. 

"We've got several disciplines working together at a level that's just unparalleled," she said. "We can do something important, and that's capturing multiple complements of a complex system, as it's changing. And, at a super-high resolution," Meredith said. 

To understand how plants allocate carbon, the team will use a small molecule called pyruvate to feed a specific type of carbon atom – an isotope called "carbon 13" – directly to the soil, roots and leaves. The movement of carbon 13 through the ecosystem will be traced using sensors embedded in the plants and throughout the biome, UA News reported. 

The researchers also plan to use another approach: pulse labeling. By injecting a burst of carbon 13 in the form of gaseous carbon dioxide into the biome, they can trace how the plants, soil and microbes absorb and move the carbon.

“We want to know if the measurements from the bottom-up match those from the top-down,” Meredith said. 

This method is not only unique, but also useful for researchers who intend to model ecosystem processes in a pinpointed way. Water will be traced similarly as researchers tracking the movement of water from soil pools to the top of the atmosphere. The team will have four analyzers in one place, which is rare, Meredith said. 

And, as part of the project, Meredith will focus on what microbes in the soil are doing as the rainforest dries out. They'll try to see what the microbes are eating, and how they communicate to each other. "We'll see how they talk to each other, looking at signaling is really new," Meredith said, noting that the project will track how microbial communities use VOCs to communicate. 

They'll do this with support from the UA Office of Research, Discovery and Innovation and the U.S. Department of Energy User Facilities, Meredith said. "It's really hard to track and understand how microbes live in, and on the leaves and roots. Using these isotopes methods we hope to look under the hood a bit," she said. 

Meredith said they expect to find that plants use carbon in different ways under stress. She also expects plants, soil and microbes to create different VOCs than they do under normal conditions, and that the team could possibly even discover new types of VOCs, Meredith told UA News.

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"Volatile organic compounds are in lotions, deodorants, shampoos and more," Adams said. "If people were allowed in the rain forest during the experiment, the volatile organic compounds they give off could make it difficult for researchers to decipher what’s coming from people and what’s coming from the rain forest."

VOCs are important in atmospheric emissions, and these compounds can also create haze, and some compounds can interact with nitrogen to create ozone, which is also bad for human health. 

The researchers said this kind of science can only be done in a place like Biosphere 2.

“What I like about Biosphere 2 is that it has grown naturally for so long,” Werner said, adding that the ecosystem's longevity makes it a more reliable proxy for a rain forest than a lab.

"Biosphere 2 is a place of limitless possibilities and hyper imagination,” Meredith said. “And for me, my interests are in the relationship between the atmosphere and microbes within the Earth’s biosphere (Biosphere 1). Biosphere 2 is contained, which makes it an exaggerated lab where you can directly measure the role of life on the atmosphere. It’s really powerful."

Meredith hopes that some of the information garnered from this experiment can be used to make recommendations, and help governments manage carbon, including hold to sequester carbon. "We want to do this to understand how to predict climate change better, but also to make really good recommendations," she said. "It's not just about preserving a natural state, rather people are involved in these ecosystems, and B2 is a nice lens to really understand this," she said. 

Werner got the first spark of the idea when she visited Biosphere 2 in 2011, she said.  

 It has since snowballed into an initiative driven by 50 researchers from four countries, 10 European institutions and three American institutions. The team includes researchers from diverse fields such as atmospheric sciences, microbiology, genomics, hydrology, cybe-rinfrastructure, ecology, plant science and more, Werner told UA News. 

Biosphere 2 has been the site of climate research before. 

During Biosphere 2's first experiment, when a crew of eight "Biopsherians" sealed themselves into the facility for two years, they discovered what an increase of carbon in the atmosphere—the result of high levels of carbon dioxide—would do to the coral in the ocean. As the ocean soaked up carbon above 400 parts-per-million, it became more acidic, and that impeded ocean coral's ability to build their skeletons. Later research found the same effects in coral reefs in the real word. 

Similarly, an experiment on the rainforest found that the trees and soil reacted differently to the saturation of carbon dioxide in the atmosphere, research that showed that while trees will soak up carbon, at 600 parts-per-million  they become saturated. 

Both experiments have implications for a world where the latest carbon dioxide has risen above 400 ppm. In May, the Mauna Loa Atmospheric Baseline Observatory at the National Oceanic and Atmospheric Administration recorded the highest CO2 concentration in 61 years, at 414 ppm. 

"We’re excited because we’ve always envisioned Biosphere 2 as a user facility,” Adams said. “This will strengthen that mission and show the validity by bringing together an international team."

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The rainforest biome at Biosphere 2 has become the site of a new experiment to better understand how plants and microbes respond to drought.

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