SPRUCE: Welcome to a Warmer Future

Deep in the forests of northern Minnesota, lies something that looks a little out-of-this-world. Long boardwalks connect a series of octagonal pods that serve as gateways into the future. But this isn’t some secret alien colony. It’s a large-scale research project that’s studying the effects of climate change on the peatland ecosystem. The project is called the Spruce and Peatland Responses Under Changing Environments experiment, or SPRUCE. The goal of the project is to understand how climate change impact this delicate landscape. In this episode, you'll hear from members of the SPRUCE team about what they've learned from the experiment so far. 

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IVERSEN: We are building not just one future, but a range of possible futures.

GRIFFITHS: It almost looks like alien pods have come down from space and set up in the peatlands.

WESTON: It's easy to have a pessimistic view. But if you look into the details, and you listen to what the biology is telling us, sometimes there's glimmers of hope.

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JENNY: Hello everyone and welcome to the Sound of Science – the podcast highlighting the voices behind the breakthroughs at Oak Ridge National Laboratory.

MORGAN/JENNY: We’re your hosts – Morgan McCorkle and Jenny Woodbery.

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JENNY: Deep in the forests of northern Minnesota, lies something that looks a little out-of-this-world.

MORGAN: Long boardwalks connect a series of octagonal pods that serve as gateways into the future.

JENNY: But this isn’t some secret alien colony. It’s a large-scale research project that’s studying the effects of climate change on the peatland ecosystem.

MORGAN: The project is called the Spruce and Peatland Responses Under Changing Environments experiment, or SPRUCE.

JENNY: SPRUCE is a collaborative effort among Oak Ridge, the U.S. Department of Agriculture’s Forest Service and upward of 90 university and laboratory partners.

MORGAN: The goal of the project is to understand how warming temperatures will alter this special landscape.

JENNY: Peatlands are wetland ecosystems that occupy about 3 percent of the Earth’s surface. One of the things that makes this ecosystem unique is that the soil is completely made up of dead plants. The cold, wet conditions make it difficult for these plants to decompose.

MORGAN: Because it doesn’t decompose, this dead plant material – also known as peat – stores a vast amount of carbon.

JENNY: With global temperatures on the rise, scientists are concerned that this waterlogged material could start drying out and decomposing, releasing untold amounts of greenhouse gases into the atmosphere.

PAUL HANSON: While peatlands themselves cover a relatively small amount of the global land area, they store a huge disproportionate amount of carbon at the global level, and they represent the largest terrestrial stock of carbon on earth. And with anticipated global warming, this large stock of carbon, which has accumulated since the last glacial period over some 10 to 12,000 years, it is potentially subject to be re-released back to the atmosphere through warming induced decomposition in the form of carbon dioxide and methane. Those are two greenhouse gases, which if they are released back to the atmosphere, will exacerbate the warming of that atmosphere.

MORGAN: That’s Paul Hanson, who leads the SPRUCE project. He’s an ecosystem scientist and a corporate fellow at ORNL.

JENNY: Scientists try to predict the future through experiments all the time. They collect data about current and past conditions and use computer models to project possible outcomes.

MORGAN: In our last episode, we took you to Arctic Alaska to explore the unseen world of climate change with the Next-Generation Ecosystem Experiments, or NGEE Arctic.

JENNY: The NGEE project is studying how rising temperatures are affecting the plants, roots, soil and microbes of the Arctic tundra. It uses a combination of field work and computer modeling to better understand what the future may hold.

MORGAN: SPRUCE also focuses on examining how rising temperatures affect vital parts of the peatland ecosystem. But instead of relying on computer models to predict the future, scientists have literally built possible futures to study.

JENNY: How do you build the future? This is where those alien-like pods come in. The pods are actually enclosures where scientists are manipulating the temperature of the air and soil.

COLLEEN IVERSEN: Paul Hanson put a sign over the door of each of the enclosures, and it says, “Welcome to a warmer future.” Each of the enclosures, it's kind of like a greenhouse without a top, so we get rain and snow coming in. But they're 40 feet in diameter, and almost 30 feet tall. It's like a room. And it encircles the bog, and the trees and the shrubs and the soils and the microbes that were already there. We didn't dig anything up and put it back anywhere, we built walls around it, and we add hot air, and we add below-ground warming with these heating rods. And so it's kind of like looking at an intact system, but giving it the climate of the future.

MORGAN: That’s Colleen Iversen. She’s a senior staff scientist in ORNL’s Environmental Sciences Division and has been involved with SPRUCE since the beginning.

IVERSEN: Something that the Department of Energy really encouraged us to do is to make observations that will directly inform mathematical models, making a virtual world to project the future. One of the things we were talking about, as we were starting to design this first experiment was, how warm should we make the enclosures, you know, what future do we want to target? Instead of just having one amount of warming, the modelers suggested to us to have a range of warming. So, we could think about a response surface. At what temperature do the microbes do this, at what temperature do trees start to die? Or at what temperature might we expect more shrub growth. And so instead of one amount of warming, we have five different warming levels: one of them is no warming at all, but it’s surrounded with the enclosure. And then we have plus 2.25 degrees Celsius, plus 4.5, plus 6.75, and plus 9.

JENNY: Convert those temperatures to Fahrenheit and you’ve got enclosures that are 4, 8, 12 and 16 degrees warmer than the unwarmed plots.

HANSON: It gives us a sense of real observations of what a plausible future climate might do to this particular important, carbon-rich ecosystem. One of the key aspects of SPRUCE is that we're trying to combine our empirical, on-the-ground measurements, through modeling to give us a tool with which to extrapolate what a true future might look like.

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MORGAN: The SPRUCE experiment is in its sixth year and scientists are starting to get glimpses into the future with the warmed plots.

JENNY: Researchers from ORNL and other institutions journey to SPRUCE several times a year to take measurements and conduct experiments.   

MORGAN: SPRUCE is located on a bog in the Marcell Experimental Forest in Minnesota.

JENNY: The site itself about the size of three football fields. The waterlogged peat makes the ground challenging to walk on, so a series of boardwalks were built to connect the experimental enclosures.

MORGAN: Soil, roots, microbes, plants and water – the team is looking at all of these elements to understand how the warmer temperatures are affecting the ecosystem.

JENNY: We talked to several members of the SPRUCE team to explore what it’s like to do research there and what they’ve learned so far.

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JENNY: As you’ve heard, peat is a very unique type of soil because it’s made up of layers and layers of dead plant matter. So, you basically have plants growing within dead plants.

MORGAN: In the peatlands, the plant life largely consists of mosses, shrubs and some trees. But before we talk about the plants, let’s look at what’s happening with their roots.

JENNY: That’s what Colleen Iversen is focused on at SPRUCE.

IVERSEN: I'm interested in whether warming, or warming in combination with extra or elevated carbon dioxide concentrations, whether that affects when roots are born, how much they grow, and when they die. I'm also interested in understanding whether these climate change treatments affect the amount of nutrients available for roots to take up to help the plants to survive and grow.

JENNY: You may remember Colleen and her passion for roots and soil in our last episode. The peat she’s digging into at SPRUCE is totally different from the Tennessee clay or Arctic tundra soils that she researches.

IVERSEN: The soil around here is sand and silt and clay particles with organic matter, which is the carbon from dead leaves and dead roots and dead animals all mixed in. That's what gives us the blackish color. But in the peatland, there's no sand and silt and clay until you get down like 12 feet, you know where the glacial till was. It was a basin and then plants started to you know, come in and water and it’s sort of like a lake and then plants filled in and then they died but didn't decompose because it's wet. And so, they just sink to the bottom and then more and more and more. And then you end up with, you know, 12 feet of peat.

MORGAN: Not only are the layers of peat very deep, they’re also very old. The peat bog where SPRUCE is located is estimated to be about 12,000 years old.

JENNY: What’s it like doing research on an ancient peat bog? Colleen and her colleagues use different methods to collect samples and take measurements at the site. Some of those include special robotic cameras and root traps.

IVERSEN: And one of the cool things that I think about measuring things at SPRUCE is of course, I get to see what's happening below ground that most people don't get to see. These cameras are carried around by little robots in each of their tubes. And so this robot will carry the camera around and take pictures throughout the soil profile and send those back to us so we can see when roots are born. But we can also see what the fungi are doing. I get to to do that with cameras but I also get to do it when I pull these root traps out, right? So, you pull out the peat and it's dripping and has all of this sort of brown water coming out that's really high in carbon. And you can sort of reach your arm down into the squishy peat all the way up to your armpit if you wanted to. So, like you're reaching down thousands of years, you know, peat, that's thousands of years old to sort of to make these samples and I just think it's really cool.

MORGAN: One of the interesting responses to the warmer temperatures that the team has observed is the increased presence of a shrub related to blueberries.

IVERSEN: The responses that we’ve seen of this ecosystem in response to warming have actually been belowground. There’s some interesting things happening that you can observe aboveground. We've seen that warming has really decimated these poor little sphagnum mosses that grow along the surface of the bog. It's too hot and dry for them. And so shrubs in the blueberry family have actually taken over. And those shrubs make very, very, very tiny roots almost as fine as a human hair. And we have found that the growth of those roots, after this sphagnum has been decimated, has increased 130 percent for every degree of warming that we've had in this first experiment. And also that that increase in root growth is 20 times more than other folks have seen in comparable experiments in upland systems. And so we will often see these ericaceous shrubs take over in peatlands have been disturbed or been dried out. But we haven't really understood the mechanism as well for that. And so we wonder now that we're seeing this really strong increase in root growth of these shrubs in the SPRUCE experiment, if an increase in root production is one of the ways that those shrubs have been able to get a toehold in other experiments where we've seen them take over.

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JENNY: The effect of warming on sphagnum mosses is particularly concerning because the moss plays a critical role in the peatland ecosystem.

DAVID WESTON: We consider the mosses to have a disproportionate role relative to other plants in that ecosystem because together they’re anoxic meaning, you know, not a lot of oxygen because it's a waterlogged ecosystem, and typically cold environmental conditions, it keeps the dead organic manner in what we call a recalcitrant form. So this dead plant biomass as it dies, and it goes into the ground, or in this case, into the bog system itself, the moss itself, so the sphagnum mosses, the way it interacts with its environment keeps microbes from degrading it. And when they keep those microbes from degrading that that organic material, that carbon doesn't get released back into the atmosphere.

MORGAN: That’s David Weston, a plant biologist and senior scientist at ORNL. He says there’s a particularly vivid but gruesome way to understand this kind of environment.

WESTON: And the way I usually show this in the slideshow, is I have the, the bog men, right. And so if you search online, if you look at the peat bog men, you know, these are folks that have been around, you know, for 1,500 years or so that were either died or executed. However, it happened in a peatland. And that when they recover them, in some cases, they're reported to the homicide department, because they're so well preserved. And so that's how well these ecosystems actually preserved this dead organic material, whether it's a human or an animal or dead plant material.

MORGAN: Don’t worry, the SPRUCE team hasn’t found any bog bodies in their field work. David is much more interested in those tiny mosses. He became captivated by moss when he first visited the SPRUCE site.

WESTON: All through my career, it's always been trees, or crop plants, or whatever we're studying. And I can remember, the first time we visited the site. And we went in and all the plant biologists were looking at the trees, or we're looking at the shrubs. And I was the new person at that time. So I was just sort of hired in, very junior, and I'm standing on all this moss, I've never studied it, I've never been interested in it. And the more you just observe it in that ecosystem, you just see how profound of an effect it has on the functioning of that ecosystem.

JENNY: His expertise in mosses has gained him a pretty amusing nickname from his colleagues - Sphagnum P.I.

WESTON: If you go into our greenhouse lab area, somebody took a Tom Selleck photo, which I'm proud to be associated with, and then pasted my head on there.

MORGAN: Silly nicknames aside, we asked David to give us the scoop on what makes these mosses so special.

WESTON: If you look at mosses, remember, they don't have a real root system, like a typical tree or shrub. But what they do have is they have a really neat network of above ground material, we call them leaflets instead of leaves and stems. And if you really zoom in, in your mind's eye onto the top of a leaf, like you would think of a regular tree, these would be much different in the fact that the cells that photosynthesize, are surrounded by dead cells that you can't see, that have a pore. And in these dead cells, we call them hyaline cells, they're filled with water. So because these mosses don't have this extensive root system, they've adapted these dead hyaline cells to hold water in there, because they can't bring water in from the roots.

JENNY: The tiny leaves of the moss provide a refuge for microbes trying to escape the acidity of the bog.

WESTON: What's cool about this is within those hyaline cells, it's a more buffered pH. And so instead of 3.8 pH in there, we think is more like 5.7. And what it does is it provides an oasis for microbes to go in there. So microbes that do not like this really low pH can now go into and associate with that plant. And this is what I find super exciting about this particular plant in general is it has so many of those cells, like upwards of 50 to 70 percent of those cells are actually not photosynthesizing, they're holding this water and these microbes in this microbiome. Together, they're, they're cooperating right, they’re cooperating in a symbiotic fashion, so that they're helping the plant to survive in this environment. But more importantly, it's providing nitrogen to the plant through symbiotic nitrogen fixation. And it can fix it into a usable form of nitrogen that it gives to the plant, and then in return the plant is giving sugars and carbohydrates back to that microbe and some other rare nutrients that we're now just discovering in our, in our laboratory studies.

MORGAN: In the warming scenarios, the sphagnum moss is struggling to survive. The team has also noticed a shift in the relationship between the moss and the microbes.

WESTON: So the amount of fixation is changing. And not only is the fixation itself changing, that is the nitrogen going to the microbe and then to the plant. But the types of microbes the plant is associating with is changing, and it appears that is changing with those that are not fixing nitrogen, or not fixing nitrogen as much, as it would.

JENNY: While these finding sound a little bleak for the sphagnum mosses, David and his colleagues are experimenting with ways to boost the mosses’ resilience. And interestingly enough, this experiment was inspired by mice.

WESTON: We got this idea from the mouse microbiome experiments where they would take mice, and they would extract the gut microbiome from mice, and they would put them into what we call a gnotobiotic mouse. Just think of a mouse that has been raised in a laboratory where it has very few microbes in there. So, it's almost like a mouse without microbes. And they do these microbiome transfers. And when they do that, you can change the mouse physiology. So if you take, say, a microbiome from an obese mouse, and you put it into a gnotobiotic mouse, even feeding it a normal diet, it's still gaining weight. So, we got this idea that we do the same thing with these sphagnum mosses. So, we went to the SPRUCE site, and we're taking moss that are in this really high warming scenario. So, this 9 degrees C scenario. And we're taking sphagnum from just the ambient conditions that doesn't have any warming, we bring those plants into the laboratory, we grind them up, we extract those microbes out of them as best we can. And then we have laboratory grown sphagnum that have no microbes whatsoever. And we do these microbiome transfers. And what we're finding that we're really excited about is that when you take these microbes that came from this warming environment, you put them on this moss and then you hit them with a really strong heat shock, that they're doing just fine, meaning they're more resilient, they're operating more like their pretreatment state. And so, I find that encouraging, even though we're losing some of these mosses, and we're losing species in these systems, that there might be interactions that we just haven't discovered yet that may make the system more robust. And more specifically, mosses more resilient to climate change. And that's our hope.

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MORGAN: As temperatures rise in the peatlands, decomposition will be the driver for the release of greenhouse gases.

JENNY: Natalie Griffiths is one of the scientists at SPRUCE who is studying the rate at which the organic material is decomposing and contributing to the carbon stored in the peat.

MORGAN: Studying decomposition is a years-long process.

NATALIE GRIFFITHS: We put these litter bags out, we just like let them decompose over multiple years, and then we come up and then we pull them out of the peatland. We have to find them - and then pull them up and bring them back to the lab.

JENNY: And it turns out that stepping into a warmer future is exactly that – hotter than you might expect.

NATALIE: We come with all of our big coolers, we’re walking down the boardwalks, you have a little key to enter the door, you pull the door open, you come into this chamber. And sometimes we do this in the summer, it's just so hot, it's already hot in the summer there. And then if you're going into the chamber that's plus nine degrees C, it's just, it's very hot. And so that's one of the things that even when you're up in Minnesota, you don't really expect to be like, very, very hot, but yeah, in the summer you can be.

JENNY: Once they retrieve the litter bags, the samples go back to ORNL to be analyzed. So far, while the warming has had an effect on many aspects of the SPRUCE experiment, the decomposition rate hasn’t changed much.

GRIFFITHS: We've found that warming is not increasing those decomposition rates to date. And we expected that to happen. It's just sort of a straight up. Warmer temperatures might increase the metabolism of the microorganisms, bacteria, the fungi that are doing the decomposition process itself. And so, we'd expect faster decomposition, but we're really not finding that yet. And so, the question is sort of what's going on there. And we think that so far, we're finding that the chemistry of those compounds, the different leaves we are studying, is really the limiting factor more so than temperature itself. And so potentially, as those leaves continue to degrade in the peatland, we might see the temperature effect coming out as we continue to study that. And so, we've only really studied the first couple of years of the decomposition rate, we're going to study it for the whole 10-year duration that SPRUCE is going to be running and so sort of see if we see changes over the longer duration.

MORGAN: Natalie is also studying how carbon cycles in the water at the site.

GRIFFITHS: We're looking at carbon in the water itself. And so, if you are making tea, and you have your tea bag, and if the tea releases these organic matter compounds into the water, the tea gets darker and darker as you leave your water, your tea steeping for longer. And so, the same thing happens there that leaves, the peatland mosses that are in the water, they release compounds into the water and stain and darker and darker and so we're seeing with warming that that water is getting darker and darker as more carbon is getting into the water itself.

JENNY: What they’ve found is the warming has increased the amount of organic carbon in the water.

GRIFFITHS: So the overall finding right now is we are finding with warming, there's more organic carbon in the water itself. And so in some ways you could correlate that with the water is getting a bit darker in terms of because that coloration is related to those carbon compounds. And the question is, where is that carbon coming from?

MORGAN: Natalie’s colleague Jeff Chanton, a carbon cycle scientist from Florida State University, is conducting experiments at SPRUCE to look into this question.

JEFF CHANTON: SPRUCE is a very high-tech site. And they have these large establishments that regulate the temperature and the CO₂ concentration in the air above the soil. But we're kind of low tech, and what we have are these little, called piezometers. And they're basically little groundwater wells. And we got them down to specific depths, we have them at 25, 50, 75, 100, 150 and 200 centimeters down deep in the soil. We draw water up from these piezometers, and we, we put them in sampling containers and preserve them. And then we bring them back to the lab at Florida State University. We look at the CO₂ that's released into the belowground pore waters by bacteria. It's like a bacterial breathalyzer. And so, we can see what the bacteria have been eating. Are they eating the peat, which is what the carbon is stored on? Or are they eating surface carbon that's been recently photosynthesized and flows down in the pore water? In most peatlands today, most of the respiration at depth in the peat is driven by modern surface carbon that's been moved downward through the waters to deeper depths. But as these temperatures warm, what we're finding is that more and more older carbon is appearing in that dissolved belowground CO₂ pool. And that's indicative of the peat itself starting to break down.

JENNY: The team is looking into how different forms of carbon being released into the ecosystem.

CHANTON: And one of the interesting things that we're finding is that as the peatlands warm, they’re still beginning to lose CO₂, but they're also losing methane at a faster rate. And so, the peatlands are becoming more and more methanogenic, that is more of their carbon decomposition produces methane as they warm.

MORGAN: This finding is troubling because methane is a greenhouse gas that is up to 30 times more potent than carbon dioxide.

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MORGAN: We wanted to know whether SPRUCE researchers had been surprised by what their studies have shown so far. Paul Hanson said their data has both confirmed some hypotheses and revealed some trends that they didn’t anticipate.

HANSON: Throughout this period, we've begun to retrieve findings from the SPRUCE project. And some of them were expected and some were unexpected. But the key findings that we've published on to date include direct evidence that active warming will increase the growing season length for this particular kind of ecosystem, and probably for others, both in terms of springtime advance in terms of earlier springs, but also an extension of the fall.

JENNY: For Colleen Iversen, observing the changes in the ecosystem has also prompted new scientific questions as the experiment has progressed.

IVERSEN: When we originally started thinking about how the ecosystem would respond to warming or elevated carbon dioxide, I sort of was thinking about not just the shrub response, but also the trees, there's spruce trees, black spruce and larch trees there. And I thought they would respond as well. But actually, what we've been seeing is that these shrubs that are related to blueberry have really been the dominant driver of change in this ecosystem. We saw the mosses decline, the shrubs increase, and really no effect of warming on the trees, or at least no positive effect of warming on the trees. And so that was a little surprising to me. And so interesting from the context of ecosystem function, because the shrubs and the trees have very different physiology, very different fungal associations, very different rooting depth distributions. And so, it's interesting to think about the implications for the carbon cycle.

MORGAN: At times, witnessing the scope of changes prompted by a warmer climate can be discouraging, as Jeff Chanton explains.

CHANTON: It's not surprising that the peat will start to decompose at this higher temperature. But I think it is surprising that the decomposition mechanisms which shift towards more and more methanogenesis. And so, the, the effect of this decomposition, or the effect of the warming temperature is, is a double whammy, if you will. You have the shift from the peatlands being a carbon sink to a carbon source, and at the same time they're producing, see more and more methane. It's always a double whammy in effect, it is doubly bad.

JENNY: But on the other hand, the knowledge gained from SPRUCE means that we are better prepared for a warmer climate. David Weston’s experiments with increasing the resilience of mosses have given him a new and brighter perspective on the future.

WESTON: It's easy to go into that system and say, you know, this looks awful, you know, the future scenarios do not look optimistic because we're losing one of the predominant keystone species of that system. And it's easy to have a pessimistic view. But if you look into the details, and you listen to what the biology is telling us sometime, there's, there's glimmers of hope.

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MORGAN: Thank you for listening to this episode of the “Sound of Science.”

JENNY: We hope you enjoyed this episode and will leave us a review wherever you get your podcasts.

MORGAN: Also, if you’re interested in hearing more about the fascinating world of roots, be sure to listen to our upcoming “Soundbite” on a project named FRED.

JENNY: Until next time!