ScienceMatters - Season 3, Episode 8 - Digging Up Climate Clues in Peat Moss
Gardeners love peat moss; it’s great for growing. But Joel Kostka, professor in the School of Biological Sciences and the School of Earth and Atmospheric Sciences, wonders if it serves as a warning sign for the impact of climate change on plants and microbes. He travels to a unique experimentation site in Minnesota to find answers to his questions.
Renay San Miguel: Hello and welcome to ScienceMatters, the podcast of the Georgia Tech College of Sciences. I’m RSM.
Canadian industry video: Industry professionals recognize Canadian sphagnum peat moss as the most superior soil-less media base for horticulture processes.
Renay San Miguel: You’re listening to a video from a Canadian horticultural company trumpeting the benefits of that country’s sphagnum peat moss.
Canadian industry video: This is due to its homogenous composition, high structural stability, high capacity for water and air retention, adjustable PH, and nutrient status.
Renay San Miguel: That’s why gardeners around the world love peat moss. It’s great for growing things. But another group, scientists, holds peat moss in high regard as well.
That’s because it may serve as a warning signal for Earth’s climate.
2016 Georgia Tech podcast: Here’s what the peat looks like, so that’s pretty deep down, that’s what happens when it sinks down through the peat column, as it sinks down it buries and degrades.
Renay San Miguel: That’s Joel Kostka, professor in the School of Biological Sciences and the School of Earth and Atmospheric Sciences, and he’s digging up peat moss at an Oak Ridge National Laboratory facility in northern Minnesota.
2016 Georgia Tech podcast: It’s probably about at least 5,000 years old, maybe 8,000 years, so we can date this peat using radiocarbon analysis as you would date a fossil, human fossil or otherwise.
Renay San Miguel: This audio is from a 2016 podcast by Georgia Tech senior science writer Ben Brumfield. Later that year, Kostka was part of a team publishing research that provided a slight bit of good news about climate change. Namely, the methane trapped in ancient peat moss was showing no signs – yet – of being released into the atmosphere in large quantities as the Earth’s climate grows warmer. That’s important since methane is a much more potent greenhouse gas than carbon dioxide.
What about other gases and nutrients in that peat moss? What about the other plants and soils in the environment?
In 2018 Kostka’s Microbial Ecology Lab team was awarded a National Science Foundation grant to find the answers to those questions and continue its studies of the microbes in peat moss.
Joel Kostka: It turns out that peat moss could be one of the most important plants to the global carbon cycle. It could store more carbon arguably than any other plant on earth, and the reason for that is that the carbon that’s stored in freshwater wetlands and peatlands is largely from peat moss. Peat moss produced that carbon in these thick peat deposits in peatlands across the world.
Renay San Miguel: This is about more than peat moss, however. Not a lot is known right now about how climate change is affecting the microbial community. In fact, another School of Earth and Atmospheric Sciences professor, marine microbiologist Frank Stewart, co-signed a letter with 30 other scientists in summer 2019, encouraging the science community to boost microbial studies in climate science research.
For Kostka, his NSF grant is a chance to find if the environment is reeling in other ways from warming temperatures. How is climate change affecting carbon, nitrogen in our soil? Is it winnowing down microbial diversity, and affecting key functions they provide for certain plants in the environment?
Microbiomes are all the microscopic living things in a certain environment, including our bodies. When we get sick, we want to know everything about those microbiomes.
There are plenty of questions to answer about the planet’s microbiome as well.
Joel Kostka: I would say our laboratory studies the ecosystem services or functions provided by microorganisms. And microorganisms are often the great decomposers in ecosystems, breaking down dead and dying organic matter and producing greenhouse gases. And I would say that the—when I teach introductory microbiology here at Georgia Tech, I always say that the greatest way that microbes impact climate is just by producing and consuming greenhouse gases, and that’s largely through these natural processes like decomposition that we study in my lab.
We largely focus on soils and sediments, which is often—these are often repositories for dead and dying organic matter. Plants die and they fall to the forest floor. Wetland plants die and they’re broken down in the soils.
Renay San Miguel: Why we do study freshwater wetlands or peat lands, this mix of wet and dry that’s going on and how that impacts the microbes?
Joel Kostka: Yeah, we focus on freshwater wetlands because they’re so important to the release of greenhouse gases on earth. So about one-third of all the methane—methane is an important greenhouse gas—that’s released annually from the surface of the earth is coming from freshwater wetlands. And if you include rice paddy soils, which are also a freshwater wetland, albeit a cultivated one by humans, that would be over half of all the methane that’s released annually from the earth’s surface is coming from some freshwater wetlands. So we want to understand what controls that process and that release of greenhouse gas.
Renay San Miguel: How are those ecosystems vulnerable to that? I mean, what’s the biggest risk that you’re studying?
Joel Kostka: Freshwater wetlands are dominated by plants. They’re vegetated ecosystems, right? And largely grasses. Grasses that withstand wet environments are present. Grasses and other plants. The hypothesis is that as the climate warms, plants will become more active and they will suck more water out of the soil essentially. Through evapotranspiration they’ll draw more water out of the soil and this will lead to a drying out of wetland ecosystems. So the thought is as climate warms, freshwater wetlands will dry out and that will lead to the release of more greenhouse gases.
And the reason for that is now—one of the reasons why we think that freshwater wetlands store so much carbon is because they’re cold and because they’re wet. And in climate models we often predict how much greenhouse gas is going to come out of the soil based on whether it’s wet or not. And the reason for that is wherever it’s wet, oxygen diffuses more slowly into the soil. And so oxygen is used up fast by microbes and there’s not much oxygen available for respiration, which releases greenhouse gas. So if it’s wetter, organic matter breakdown slows down, less respiration occurs, so you have more carbon going in as photosynthesis than carbon coming out as respiration.
Renay San Miguel: Some of those microbes also have other things to do besides digest organic matter. They sometimes work with plants to infuse them with important nutrients, and Kostka and his team have discovered that that process may indeed be downgraded by climate change.
Here he talks about microbes and the importance of nitrogen fixation, a method of converting nitrogen gas in the atmosphere in a way that can be used by plants.
Joel Kostka: So I mentioned that microbes are the great decomposers of ecosystems, breaking down dead or dying organic matter. They are also really important to the cycling of major nutrients, nitrogen and phosphorus in ecosystems. And we know that a lot of these freshwater wetlands that store so much carbon on a global scale are nutrient-poor. They have very low amounts of nitrogen and phosphorus. So it’s thought that microorganisms are very important to the input of nutrients into these ecosystems. They provide a supply of nutrients to the ecosystem, especially nitrogen. And the hypothesis is that microorganisms supply nitrogen to these freshwater wetland ecosystems through a process called “nitrogen fixation.” This is a process that only microbes do. So you and I can’t fix nitrogen, and plants also can’t do it themselves. Only microbes fix nitrogen. So you might have heard about leguminous plants, for example, legumes. So for example, soybeans are legumes and these plants have special structures in their roots that cultivate microbes to fix nitrogen. So they don’t do it themselves; the microbes do it. In the same way in these freshwater wetlands there are microbes that can fix nitrogen and serve as a major input of nutrient into the ecosystem.
So we’re concerned that that service that the microbes provide to the ecosystem, adding nitrogen, may be affected by climate change, and indeed we have evidence now that that occurs.
2016 Georgia Tech podcast: You hear me cutting through the roots here, they have really thick roots.
Renay San Miguel: We take you back to that 2016 visit to Minnesota, and the SPRUCE facility run by the Oak Ridge National Laboratory. Yes, there are plenty of spruce trees in Minnesota, but in this case SPRUCE stand for Spruce and Peatland Responses Under Changing Environments. Twenty acres of the Chippewa National Forest is protected for experimentation.
Joel Kostka: What’s really unique about this climate change experiment is also that it involves whole ecosystem warming. So these giant chambers, enclosures that cover the whole ecosystem, all the trees, all the shrubs, all the plants. They’re open-top enclosures and that’s because these particular freshwater wetlands, bogs, get all of their nutrients from the atmosphere, from rain and from snow as well as from microbes. And so they have to be open at the top in order to get their nutrients.
These chambers are warmed from not—not warmed at all, all the way up to 9 degrees Celsius above the ambient, which is a lot warmer than the surroundings. So in these—in this spruce experiment we have been studying, of course, how microbes change with climate. Warming and carbon dioxide enrichment. We have seen evidence in the field that carbon dioxide—that more carbon dioxide and more methane are coming out of the bog with warming. So warming causes an increase in the amount of greenhouse gas release, and we have various measurements from my group and from other groups around the country that have shown this. That as we warm the whole ecosystem we see more greenhouse gas coming out of the soil.
So we conducted an experiment in the laboratory to look more into those controls of greenhouse gas release to verify the field results and find out which microbes might be involved in releasing the greenhouse gas and further understand the controls of that process.
Renay San Miguel: Kostka explains the experiments he and his team conducted. Some of the conclusions have given him pause regarding microbial diversity and climate change.
Joel Kostka: And so what we did was basically we just took peat from the surface soils up there in Northern Minnesota, we put it in test tubes, and we warmed that peat from, you know, no warming all the way up to 40 degrees Celsius. So a big temperature range. We warmed the peat and we studied how much greenhouse gas came out of the peat in the test tube, and then we also looked at how the microbes change with warming.
And what we found was a huge decline in microbial diversity with warming and also an increase in greenhouse gas release as we had seen in the field.
Another important observation that we’ve seen is it really matters which greenhouse gas is coming out of the freshwater wetland. And the reason for that is that methane stores a lot more heat than carbon dioxide. So even though a lot more carbon dioxide is coming out of these wetlands than methane, because methane stores so much heat, it really matters to climate and to the greenhouse effect.
What we see with warming, both in the laboratory and the field, is that the greenhouse gases are become more methanogenic, so more methane-rich with warming. So in other words, there’s more methane relative to CO2 as the temperature rises. And we think the reason for that is because methanogens, the microbes that produce methane, are actually—they don’t like the cold so much. It’s a—it’s a very energy-poor process to produce methane. It doesn’t produce much energy for the microbes, so it’s not really favored in the cold, and so then as the system warms, as the ecosystem warms, the methanogens become more happy and they produce more methane in comparison to other microbes that are present.
Joel Kostka: We have seen in other ecosystems and in freshwater wetlands that warming stimulates methane production. I think what our group is adding to that story is that the controls of that ratio of methane to CO2. That’s what we haven’t understood in the past is what are the microbes and specific microbial processes that will produce methane versus other gases like carbon dioxide?
And so what’s new about this is that we quantify that ratio. Another—something else that’s new, perhaps more important to the microbiology is the decline in diversity. That has not been shown in the past. That there’s a decline in microbial diversity with climate warming or with, in this case, simulating climate warming in a test tube. We did this experiment in the laboratory.
We have some data from the field that also suggests a decline in—or indicate a decline in microbial diversity with warming.
We’re talking about microbial species, different types of microbes that are present. And the reason why we think that’s important to ecosystem function is because it makes sense that with disturbance, with any kind of change or perturbation, when an ecosystem responds you would expect that if you have more types of organisms, large and small, that they will do better at responding to extreme conditions or to changes, to disturbances.
So generally, in ecology we think that a more diverse ecosystem is more able to respond to changes.
And so therefore, if microbial diversity is going down, we think that that system will be less able to deal with changes like changes in weather, seasonal changes from cold to warm that happen every, you know, every annual cycle. So in other words, we think diversity is proportional to the health of the ecosystem. And so the hypothesis is that as microbial diversity declines with warming, that ecosystem will be less able to function and less able to deal with disturbances and problems that arise.
Renay San Miguel: We mentioned before that scientists have some gaps to fill regarding what they know about climate change and what it’s doing to microbes.
In Kostka’s view, researchers are also playing catch-up when it comes to knowledge of plant microbiomes in general.
Joel Kostka: First of all, the study of plant microbiomes is very much in its infancy. We’re probably at least 10 years behind the study of the human microbiome, and so we’re still in—we’re still trying to discover what types of microbes are present and what they do for plants. OK? We’ve been doing that with this important peat moss plant for at least five years now and we feel like we have a good idea of what microbes are present and why they’re important.
Renay San Miguel: Leading-edge technology allows Kostka’s team to add to the bigger microbiome picture. Remember Kostka talking about nitrogen fixation, when microbes enable plans to use nitrogen? PCR, or polymerase chain reaction, is used to make copies of the DNA of the genes that code for nitrogen fixation. He and his team are adding to a global database of those genes to share with other researchers.
This comes up again when I ask Kostka about how this research could lead to ways to mitigate the effects of climate change on plants and microbes.
Joel Kostka: One thing that we could do for intervention is to develop what we call “probiotics for plants.” OK? So can we develop a microbial cocktail of nitrogen fixers, for example? So the recent paper that I told you or that we talked a bit about shows that nitrogen fixation is very much affected by warming. That certain nitrogen-fixing bacteria are not favored with warming and go away from the microbiome. That’s what our data shows. And so if you could add back some of those nitrogen fixers to the plant, you know, spray it on the surface of the plant or somehow introduce it into the ecosystem, that would be one sort of intervention or mitigation effort that you could do to help the process.
That and simply just understand. You know, as I said, a lot of times we’ll predict how much greenhouse—methane in particular—is going to come out of the soil just based on whether it’s wet or not. We don’t really know all of the microbial processes and all of the ecosystem processes that lead to that whether gas is released or not.
So right now, in the models, it’s just simply how wet is the soil or not? So we want to provide microbial parameters and chemical parameters that we can then input to these earth system models that can tell us better whether gas is going to be released and how much gas is going to be released, whether it’s methane or CO2.
Renay San Miguel:
I’d like to thank Joel Kostka, professor in the School of Biological Sciences and the School of Earth and Atmospheric Sciences, for his time. His Microbial Ecology Lab website is at joelkostka-dot-net.
SunGro Horticulture produced the Canadian sphagnum peat moss video.
Siyan Zhou, a former research association, compose our theme music.
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This is ScienceMatters, the podcast of the Georgia Tech College of Sciences. I’m RSM. Thanks for listening.