USGS Outstanding in the Field: Biocrusts (Ep. 9)

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Narrator: Welcome, and thanks for joining us for another episode of Outstanding in the Field, the U.S. Geological Survey’s podcast series produced by the Ecosystems Mission Area. We highlight our fun and fascinating fieldwork studying ecosystems across the country. I’m Marisa Lubeck.

Today we’ll be discussing tiny communities that are found on the surface of the soil in the harsh environments of cold and hot deserts. These often-overlooked communities are called biological soil crusts, or biocrusts for short, and USGS scientists at the Southwest Biological Science Center have been studying them for quite a while.

Reed: Biological soil crusts are a community of mosses, lichens, cyanobacteria and a whole host of microbes that can be found almost all places where soils can see the sun. Just like plants, these communities are photosynthetic and so they need access to sunlight in order to survive. This means we find biocrusts in places where plants don’t grow as much. Places like deserts and in the arctic. Biocrusts are actually found on every continent and they are common around the world. They’re small though, just a few millimeters tall, which means sometimes you have to bend down to really get a good look. But it’s worth it, because if you look closer, you’ll see that they’re really diverse and that soil is covered with colors like bright pink and toothpaste green.

Narrator: That was USGS research ecologist Sasha Reed, describing biocrusts and how beautiful they can be if you look close enough, especially after a rain. Although most people don’t even know these diminutive communities exist, they can actually be fairly common in the arid ecosystems out West where plants cover 50% of the soil surface at most.

Reed: Biocrusts play many important roles in our ecosystems. For example, they’re very good at holding the soil together to reduce dust and soil erosion. Biocrusts produce this sticky glue that holds soil particles together and so they can make the soil really tough and resistant to erosion. Biocrusts can also bring fertility into the soil, bringing in carbon and nitrogen and other nutrients that can become available for all kinds of organisms. Another role biocrusts play is affecting how water moves in these systems, which can be especially important in places like deserts where water is such a limiting resource.

Narrator: When it rains in the deserts of the American Southwest, it can rain hard. Really hard. Because of their bumpy topography, biocrusts transform the surface of the soil from relatively smooth to rough, slowing down water flow during these big rainstorms, and limiting the amount of soil erosion that occurs. This process gives the water a chance to make its way into the soil instead of just running off. Due to their ability to build a stable layer on top of the soil, biocrusts also greatly reduce erosion because they hold the soil in place, even when huge rainstorms occur. As we have heard, biocrusts have important roles to play in our ecosystems, and their small size is an important factor in how those roles play out. But, their size also makes them vulnerable.

Reed: We’ve known for a long time that physical disturbance is a big threat to biocrusts. Trampling by vehicles or cattle or me and my dog on a hike are a problem. It’s interesting because biocrusts are so tough in some ways, holding the soil together even in the face of gale force winds, but they really aren’t very resistant to downward pressure like from feet and hooves and tires, so trampling is a problem.

Narrator: Trampling can alter the community composition of biocrusts and seems to be particularly damaging to lichens and mosses while favoring cyanobacteria, which are photosynthetic bacteria. Recovery from trampling the original biocrust community can take decades, maybe even a century or more, so disturbing these communities can come with long-term consequences.

Reed: A lot of the work that we’re doing now is also showing that biocrusts may really struggle with climatic change. We have a number of different experiments that show that increased temperature and altered precipitation can negatively affect biocrust communities and their function. And we’ve had some surprising results too. For example, we performed a precipitation experiment where we increased the amount of little pulses of water that we added. So, we gave these little bursts, and even though it was adding water to a desert, what we found was that killed off the biocrusts very quickly. This was because the little bit of activity that we got them to perform with that pulse of water made them spend energy that they then couldn’t get back before they became dry. This was a surprise.   

Narrator: When lichens and mosses that make up biocrust communities dry up due to lack of precipitation, they go dormant. When it rains, they can come out of that dormancy very quickly and start to photosynthesize, which is a very useful adaptation. However, to do that, they must expend energy to start up the biochemical machinery needed to photosynthesize. If the rains do not keep the mosses and lichens wet long enough to harness sufficient energy through photosynthesis to recoup the costs of coming out of dormancy, they could die. Another case of biocrusts being surprisingly tough and fragile at the same time.

Reed: Now is a really exciting time in biocrust restoration work and we at USGS are helping to lead new research directions in the field. Some of the work we’re doing is focused on better understanding how climatic changes are affecting biocrusts and what kind of restoration options will work best in the face of increased temperature and drought. As a scientific community we’ve gotten really good at growing biocrusts in the greenhouse and in the lab so we can make lots of new material to use for restoration efforts. However, we still need to improve our ability to have those biocrusts survive once they get into the real world, and to help do that we created a biocrust farm outside of Moab, Utah where we’re growing biocrusts for restoration purposes. We’re hoping this farm will grow hardier biocrusts and this includes work where we’re trying to explore what kind of biocrusts might be best to grow with future climate change. We’re also trying to build an international network for biocrust research. We call it CrustNet, and this network would allow us to gather information in the same way across different places and to really improve our understanding of what kind of biocrusts are where, to figure out what functions these communities are performing in those places, and to understand how these exciting communities and their important services may be changing.

Narrator: Just like large-scale plant restoration efforts, scientists and land managers are trying to move past small-scale biocrust restoration approaches and develop strategies to restore biocrusts on large tracts of public lands. This way, biocrusts can be put back into the local ecosystems where they can continue their ecological roles of soil protection, increasing soil fertility, and influencing water dynamics in the arid West. The USGS is an important player in making these actions happen.   

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This podcast is a product of the U.S. Geological Survey, Department of the Interior. A special thanks goes out to Sasha Reed from the USGS Southwest Biological Science Center and Todd Wojtowicz with the USGS Northern Rocky Mountain Science Center, and the rest of the Outstanding in the Field team. I’m Marisa Lubeck. Thanks for listening.

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