Scientists Think Restoring the Earth’s ‘Living Crusts’ Can Aid Ecosystems
Just as the human body is covered by skin that protects and nourishes it, so, too, are some of the driest parts of the Earth—they are covered by their own sort of “skin,” known as biological soil crusts.
These “biocrusts” are microbial communities that live in open areas on the soil surface and partially within the soil of arid and semi-arid ecosystems. Teaming with microbial life, biocrusts play a vital role in enabling the resident ecosystems to flourish under such harsh, arid conditions.
But despite biocrusts’ importance, it is only in the past few years that they have attracted mainstream scientific attention. Scientists who study climate change and other ecological issues have become concerned that biocrust erosion could have major unforeseen consequences.
The race is now on to both understand biocrusts more fully and to discover how to regenerate these ecological environments. Such techniques could present mankind with useful tools to combat wider climate change.
Why Biocrusts Are Important
Biocrusts exist within the top few millimeters of soil in parts of the world where harsh conditions, i.e., cold or dry environments, prevent the growth of vascular plants. Sparse ground vegetation permits sunlight to reach Earth’s surface, thereby providing conditions for a community of organisms such as mosses, lichens, fungi, and bacteria to colonize the soil.
These organisms essentially help to “knit” loose soil together, thereby providing a layer that protects the surface from erosion and dust storms, increases soil fertility, and helps soil retain moisture.
These organisms essentially help to “knit” loose soil together, thereby providing a layer that protects the surface from erosion and dust storms, increases soil fertility, and helps soil retain moisture. This living crust also helps capture carbon from the atmosphere and influences the water cycle.
Since drylands cover 45% of the Earth’s surface and support 2.5 billion people, the importance of biocrusts becomes even clearer.
Biocrusts Under Threat
There is growing evidence that climate change, droughts, and human activities, such as off-roading and agriculture, are having negative impacts on biocrusts. Between 10%-20% of dryland ecosystems have already been degraded, and that percentage is expected to grow.
While biocrusts are generally able to cope with harsh conditions, environmental changes are having a negative impact, says Sasha Reed, research ecologist at the US Geological Survey.
She warned that patterns of increased temperatures and decreased precipitation are predicted to cause conditions to become more extreme, resulting in less tolerant organisms disappearing from biocrust communities altogether.
Dr. Reed also described the vulnerability of biocrusts to direct human activity. She told The Earth & I: “While resistant to environment stresses, biocrusts are quite fragile and can be easily crushed and destroyed by human activities, such as overgrazing and construction.”
She warned that losing biocrusts would mean more dust storms, lower soil fertility, and big changes to hydrology, biogeochemistry, and biodiversity.
“What happens to biocrusts could affect all of us, because of their importance and prevalence and because of how connected ecosystems are even at the global scale.”
Once destroyed … it can take decades for biocrusts to recover.
Once destroyed, she said, it can take decades for biocrusts to recover. “An example of the impact of widespread degradation of biocrusts is the dust storms that have increasingly plagued some major metropolitan areas in the Southwest USA,” she said.
Increasing Attention
But it is only recently that the subject of biocrusts has started to find its way into mainstream scientific debate.
Corey Nelson, a research fellow at Spain’s University of Alicante, has been studying biocrusts since 2014. Nelson says that while the subject remains something of a niche area, it has been gaining increasing attention for several reasons.
“Unfortunately,” he said, “a large driver of this is the increasing global desertification caused by climate change. Many researchers and government-funding agencies are looking at biocrusts as a tool to mitigate land degradation and slow desertification.”
He added that biotech companies were also starting to realize that biocrusts could be an innovative tool to provide sustainable solutions to a wide number of problems.
“For example,” he said, biocrusts can be used for “dust suppression in solar energy infrastructure” or “to stabilize mine tailings and capture toxic metals.”
Restoring Biocrusts—Environmental Benefits
Under additional pressure from droughts and climate-related issues, biocrusts often need restoration, but it takes a considerable amount of time for nature to complete that process. So, scientists are searching for ways to speed it up.
To this end, Nelson has been working on several projects. One focuses on investigating how biocrusts form by studying the microbial interaction within biocrust communities.
“We found that biocrust-forming cyanobacteria can form a symbiotic relationship with other soil bacteria to survive and thrive in nutrient-poor soils.”
“We found that biocrust-forming cyanobacteria can form a symbiotic relationship with other soil bacteria to survive and thrive in nutrient-poor soils,” he said.
“This symbiotic partnership involves the trading of resources; the cyanobacteria provide sugars to its partners, and in return, these beneficial nitrogen-fixing bacteria provide a source of nitrogen to the cyanobacteria. Without this resource trading relationship, biocrusts would not be able to form.”
Nelson said that one way to help restore degraded soils was growing biocrust components like cyanobacteria in a lab or greenhouse setting and then seeding them in. However, many early attempts to grow biocrusts for restoration purposes ended up failing for unknown reasons.
“Applying the knowledge of the symbiotic partnership from my previous work, we were able to develop a microbial nursery to grow biocrusts that used both cyanobacteria and beneficial bacteria,” said Nelson. “We found that when we seeded degraded areas with both the pioneer cyanobacteria and beneficial bacteria together, they developed very quickly into biocrusts three times faster than only cyanobacteria.”
Currently, he is diving deeper into the impact of climate change on how biocrusts function.
“We know that microbial interactions within biocrusts are very important for their formation and functioning, but we have no idea how global change might affect these interactions,” Nelson said, adding that he has been looking at 15 years of data. “I’ll be investigating how the biocrust microbial communities in these experiments have changed over this period and using it as a peek into the future to predict how well biocrusts communities will be able to tolerate change.”
Dr. Reed is also excited about the progress being made to grow biocrusts.
“There’s work on how we can turn biocrusts into little living pellets that could be dropped from airplanes after a wildfire, which is the same way we deliver seeds.”
“There’s work on how we can turn biocrusts into little living pellets that could be dropped from airplanes after a wildfire, which is the same way we deliver seeds. It’s fun to think about little biocrusts dropping from the sky, ready to stabilize soils, add fertility, and help the ecosystem recover,” she said.
She added that there is ongoing research to better understand how biocrusts can be added to disturbed areas in liquid form, spraying photosynthesizers onto damaged soils to help biocrusts keep the soil in place.
New Tool Against Climate Change?
In addition to the benefits biocrusts provide to the land, they could also play a pivotal role in helping to combat climate change.
Along with fellow U.S. Geological Survey scientist Cara Lauria, and in partnership with the US National Park Service and Northern Arizona University, Dr. Reed is currently working on trying to quantify how much carbon dioxide is being removed from the atmosphere.
“The research will also mean we can include biocrusts into the mathematical models science uses to predict future climate, which would be an exciting research advance.”
She said, “The research will also mean we can include biocrusts into the mathematical models science uses to predict future climate, which would be an exciting research advance.”
Data is showing that the way lands are used can strongly affect the health and function of biocrusts, and also that biocrusts have high resilience.
“An improved understanding of biocrusts’ awesome role in the carbon cycle helps us put all this information into a global context,” Dr. Reed said.
Challenges Ahead
Despite the growing understanding of biocrusts and the role they play—not just in local water cycles and ecosystems, but the wider climate picture, too—there is still the belief it is something of a niche science. There is also, according to Nelson, no quick fix.
He said: “One of the biggest challenges to mitigating the detrimental impacts on biocrusts is that, at the moment, there are no easy solutions… Current solutions for the restoration of biocrust are costly, time intensive, and hard to achieve at large scales.”
With the ability to regenerate biocrusts, mankind may be able to implement measures to mitigate several pressing environmental issues. But, as with most nascent endeavors that hope one day to become mainstream, it will take funding, commitment, and time.
*Mark Smith is a journalist and author from the UK. He has written on subjects ranging from business and technology to world affairs, history, and popular culture for the Guardian, BBC, Telegraph, and magazines in the United States, Europe, and Southeast Asia.