Graduate research fellow investigates how fungi and fire enable pine savanna ecosystem to thrive

July 12, 2017
Jacob Hopkins said fire acts as a "reset switch" in pine savanna ecosystems. Credit: Jacob Hopkins | KU News Service

For most humans, fire symbolizes destruction and death. Yet nature often adapts to fire and can wield it as a creative force. For example, in the pine savannas of the southeastern U.S., fire acts as a chrysalis from which grasslands and forests spread new stems and unfurl fresh leaves.

Jacob Hopkins, a with the Kansas Biological Survey and Department of Ecology & Evolutionary Biology at the University of Kansas, researches how a hidden ally helps plants and trees in this ecosystem prosper with fire: the fungi that live in the soil and among the decomposing leaves and plant matter atop the soil, called litter.

"In the pine savannas, we think of fire as a reset switch," Hopkins said. "It prevents the pines from taking over and can prevent invasive species from coming in. It rejuvenates the ecosystem, and after the ecosystem burns we see a higher diversity of species—particularly grassland species."

With a recently announced National Science Foundation Graduate Research Fellowship, Hopkins will spend the next several years investigating the relationship between fire and the way fungi and plants in pine savannas support each other, dubbed "mutualisms." The NSF Graduate Research Fellowships pay U.S.-citizen students $34,000 per year plus a $12,000 cost-of-education allowance over three years.

"A plant-fungal mutualism is when a mycorrhizal fungi species forms an association with the roots of a host plant," Hopkins said. "There will often be an exchange of resources between the two. With grassland species, fungi give plants phosphorus and get carbon or sugar in return. But we also see mutualisms in trees, where trees get nitrogen from fungi and fungi, in turn, receive carbon or sugar. Forming these associations can help plants resist attacks by insects or pathogens, or it can increase competitive ability of the plant for growing in an ecosystem."

Hopkins' work will include field studies of pine savannas in the American southeast, where he'll assess plant and soil communities before and after burning, and see how plant-fungal mutualisms promote equilibrium and fire adaptation in the ecosystem.

"I've gone to Georgia several times," he said. "We take soil cores from different plots we've preselected to monitor bacterial and fungal diversity. We're looking at decomposition of plant litter by fungi, bacteria, as well as some microorganisms. With decomposition bags, we're looking at burned versus unburned—or how different frequencies of fire can affect the decomposing ability of fungi and how that same plant litter acts as fuel for future sites."

The KU graduate student said pine savannas are not just scientifically profound, but beautiful to behold.

Hopkins received an NSF Graduate Research Fellowship to investigate how fungi teams with fire to enable pine savanna ecosystems to thrive in the Southeastern US. Credit: Jacob Hopkins KU News Service

"You'll see these giant trees—some are 600-plus years old and have the largest trunks you've ever seen on a tree that's multiple stories tall," Hopkins said. "Right next to it, there are comparatively small grassland plants. We'll oftentimes find Gopher tortoise burrows, a threatened species. There are the red-cockaded woodpeckers—a really neat bird. We'll see rattlesnakes out there sometimes. There is so much floral and faunal diversity that you're always seeing something new and learning something just by observing. It's a good place to go for ideas for future experiments. You say, 'Oh, I've never seen that before!' You can find a lot of scientific inspiration out there."

Back in Lawrence, Hopkins will conduct tests on samples to determine what makes up the microbe and plant community of pine savannas; to find out if post-fire adapted plant-microbial mutualisms exist; to see if mutualists drive changes in the composition of litter and fuels produced; and to discover if fire favors decomposition-inhibiting plant-fungal mutualisms.

Part of the work will include genetic analysis of the vast numbers of fungi present in the soil, most of which remain undescribed by science. In just one sample, Hopkins said there could be thousands of species.

"From the sequencing, they found around 12,000 taxa—some could be the same species but there's still quite a bit of diversity there," he said. "We could identify around a thousand of them, barely 1/12th of the samples we could give a species name. By and large, we might never be able to catch up and put a name to every species."

Hopkins' new NSF fellowship will enable the research, along with aiding with tuition and expenses as he works toward a doctoral degree under the mentorship of Benjamin Sikes, KU assistant professor of ecology & and senior scientist at the Biological Survey.

"My lab is exploring how fire can shift soil microbial communities and alter rates of microbial decomposition of new fuels," Sikes said. "These data appear to show positive feedbacks, with post-fire microbes slowing decomposition, increasing new fuel buildup and thus the potential for subsequent fires. Jacob's proposed work focuses on indirect feedbacks that may be equally important. My group had thought about indirect feedbacks but had not focused on plant mutualists explicitly. His hypothesis is that fire may shift plant mutualists such as mycorrhizal fungi and nitrogen-fixing bacteria, thereby altering the production and composition of new fuels. These effects are critical to quantify because they may counteract or exacerbate direct feedback effects, thereby improving our knowledge of fire ecology and predictions for fire management."

In exploring questions about plant-fungal mutualisms and fire-adapted pine savannah, Hopkins said he hoped to earn his doctoral degree in the next three or four years.

"I eventually would like to become professor and researcher," he said. "I've enjoyed looking at how different components of ecosystems can work together, and if is altering microbial populations. How is that going to affect how are doing or affect how is decomposed? What's the bigger picture? I'd like to pursue teaching and outreach at the same time—that's just as important."

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