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The desert’s ‘skin’ is disappearing—tiny lab-grown plants could save it

The desert’s ‘skin’ is disappearing—tiny lab-grown plants could save it

Anita Antoninka dribbles a stream of water over tiny black dots on a small patch of Arizona desert. Although the soil at her feet appears dusty and lifeless, the ecologist promises there’s hidden life there, and that she will resurrect it. Within seconds, the dots unfurl into a sumptuous blanket of teeny, dark-green leaves: moss.

Each moss is smaller than a pencil eraser, and the sudden appearance of hundreds of them creates a magic carpet of life. Her trick, Antoninka says, has revealed “a functioning mini ecosystem.”

Parched or damp, this millimeter-thick layer of microbes and plants, called a biocrust, creates a protective living skin for Earth’s driest places. Biocrusts absorb carbon dioxide and release oxygen. They also fertilize the dry soil by converting nitrogen in the atmosphere into a form plants can use, encouraging larger plants whose roots anchor the soil, which in turn staves off erosion.

But in drylands around the world, biocrusts are under threat from climate change, livestock ranching, and recreation, among other human activities. Biocrusts can regrow, but the process takes centuries. If we lose these little-known but vital parts of the planet’s ecosystem, scientists say, deadly dust storms will increase, while biodiversity declines.

It’s why Antoninka—from Northern Arizona University—and a small cadre of other biocrust researchers have begun an ambitious new experiment: They’re growing biocrust on large garden plots and transplanting it to some of the U.S. Southwest’s most degraded dry areas. Importantly, the work gives scientists a chance to study how climate change will affect these resilient, yet fragile, ecosystems.

“These experiments offer a great opportunity to push the system and understand the mechanisms” that make a biocrust resilient enough to survive climate change, says Sasha Reed, an ecologist at the U.S. Geological Survey’s Southwest Biological Science Center.

How biocrusts begin

Although biocrusts currently cover thousands of square miles of soil around the world—scientists estimate that they cover 12 percent of the Earth’s land—each crust starts with a tiny microbe called a cyanobacterium. Wafted by the wind from an existing biocrust, some species of cyanobacteria can live on loose, barren soil. It doesn’t sound like much, but it’s enough to seed the beginning of a new biocrust patch.

But these otherwise rugged cells have a major weakness. As plants, they absorb sunlight, but their pale color means they don’t make melanin, a dark pigment that acts as a chemical sunblock, leaving their DNA vulnerable to damaging UV radiation. When the sun becomes intense, the single-celled cyanobacteria retreat just beneath the surface, secreting sticky sugars that create a pathway for them to move around.

Using the tip of her cement trowel, Antoninka pries up a half-dollar-size piece of biocrust from beneath the tangled branches of a mesquite and pinches it between her thumb and index finger. She points to several specs of dirt dangling beneath the clod on nearly invisible threads, evidence of the sticky carbohydrates the cyanobacteria leave behind. Without that activity, Antoninka says, this solid clump would just be more sand.

“Think about spaghetti. You slap spaghetti on the wall and it sticks. It’s the same thing here,” Antoninka says, squinting in the bright Arizona sun that reaches 85 degrees even in mid-November. “As the cyanos build this matrix, they bind the soil surface together. It’s good stuff.”

Joining the pale cyanobacteria on the wind are darker brethren. Both types of cyanobacteria add vital nutrients and stability to the soil, giving mosses, lichen, and fungi a more hospitable environment when they, too, blow in. Only when this full range of organisms begins working together does a true biocrust exist. Seasonal monsoon rains kickstart the biocrust’s growing season. As the flood waters recede, the biocrust organisms dry up and go dormant. When the next moisture arrives, the plants resurrect. Reed doesn’t know how long biocrusts can go between wettings, but she suspects it’s at least decades, if not more.

Matthew Bowker, Antoninka’s colleague at NAU, says: “All of that soil surface, if it were not held together, would be really susceptible to being blown away by wind or washed away by water,” Bowker says.

Personal losses, big gains

Biocrusts may have evolved to withstand drought, but they haven’t evolved to withstand us.

The border wall that separates the United States from Mexico runs along the southern edge of Organ Pipe Cactus National Monument. U.S. Border Patrol vans kick up a near-constant cloud of dust under the azure sky as they crisscross the park over what used to be prime biocrust habitat. When Antoninka came here to see how the traffic and heavy machinery brought in to build the wall has affected the ancient crusts, she made a predictable discovery: They’re not faring well. Every step launches a tiny cloud of loose dirt, because no biocrusts held the soil in place during the summer monsoons.

Antoninka takes the loss personally. She greets biocrusts in the field like old friends. “There’s a Heppia!” she cries, “and a Collema!” Darting here and there as she outlines the perimeter of her team’s crust collecting that day, she’s delighted to find a surprise bloom of crust. Squatting down, she looks more closely at the dark patch in the beige dust. “Oooooh, you’re so cute! Hi, guys!”

Dismayed at the widespread loss of biocrust in the Southwest by construction, fire, and other human activity, Antoninka and Bowker are growing biocrust in the lab, with the ultimate goal of creating transplant materials to help with biocrust restoration.

It’s what brought Antoninka and her team to the Sonoran Desert to harvest healthy biocrust from Organ Pipe, as well as Tonto and Casa Grande National Monuments. At all three locations, small patches of healthy biocrust are taken to serve as seed stock for the lab.

Luckily for the researchers, they only need small patches, because the organisms in biocrust are totipotent, which means any individual cell can regrow the entire organism, as long as conditions are suitable.

And suitable means harsh. Life in a greenhouse, with its constant temperature, shade, and moisture, is too cushy for biocrust; experiments there failed. Outdoor plots shelteredfrom extreme heat and aridity were enough to toughen up the tiny plants without killing them. The team now grows new crusts on jute and other biodegradable substrates so that biocrusts can be rolled up, transported, and unrolled, intact, in a new location.

“Antoninka is leading. She is pushing this field forward amazingly fast,” says Akasha Faist, a rangelands ecologist at New Mexico State University. For years, Faist says, ecologists had been waiting for biocrusts to return on their own, but now, efforts from Antoninka and others have begun to speed up this natural process.

To date, researchers have transplanted biocrusts based on where the species were originally found. But Reed’s work at USGS shows that even small shifts in temperature and precipitation can create deadly stress in these organisms already living on the edge. Instead of growing crusts under today’s conditions, Antoninka wants to grow them in hotter, drier places to hedge against an even warmer planet.

“We need to stop restoring for where we are in the present and move towards the future,” Antoninka says. “I don't know if it will work or not, but it’s worth trying.”