When excess fertilizer leaches out from croplands and urban lawns, nitrogen and other elements pollute the environment. Extensive research shows the damage that nitrogen pollution causes to soils, forests, and waterways. But a lesser-known victim — fungi — remains understudied despite its importance to healthy forest ecosystems. Undergraduate researcher Hannah Vanderscheuren BSx’22 is determined to change that.

Vanderscheuren’s fascination with fungi can be traced back to when she first opened a basic biology textbook and laid eyes on a nutrient cycling diagram. She was captivated by the complexity of carbon and nitrogen cycles — the paths these elements follow through ecosystems. “But I wondered: What does that mean on the ground?” says Vanderscheuren. “It turns out that fungi are the way to study that.” At CALS, Vanderscheuren learned that the organisms in this large kingdom, which includes yeasts, molds, and mildews, are important compo-nents in the cycles that captivated her.

Now a senior pursuing a bachelor’s degree in biology, she is exploring fungi and nutrient cycling in the laboratory of UW botany and bacteriology professor Anne Pringle. Vanderscheuren has contributed to multiple projects in the lab, but thanks to funding from a Holstrom Environmental Research Fellowship, she’s now leading her own fully funded study (with mentorship from Pringle).

Vanderscheuren’s research is inspired by an ongoing project on the East Coast, the Chronic Nitrogen Amendment Study (CNAS), where scientists are looking at the effects of excess nitrogen in forest ecosystems through the lens of fungi.

“Fungi are a part of the global carbon cycle, but in ways that are less appreciated,” says Pringle. “They underpin a lot of ecosystem processes.”

One of these processes is decomposition. Fungi are responsible for breaking down organic matter, which releases nutrients into the environment. Plants then use these nutrients to grow.

But in nitrogen-polluted systems, such as the CNAS forests, fungi composition is changing, and organic matter is building up. Species that specialize in breaking down lignin are decreasing in abundance, while species that specialize in breaking down cellulose are increasing. (Lignin and cellulose are both important structural molecules found in plants.) As a result, the compositions of both forest plants and fungi are changing, which depletes the productivity and functionality of forest ecosystems.

To complement research from CNAS, Vanderscheuren is looking at one species of Ascomycete fungi and how it physically responds to elevated nitrogen levels. In particular, she focuses on hyphae — long, branching, filamentous structures that serve as the main mode of growth for fungi — and compares the growth rates of nitrogen-exposed hyphae and nitrogen-free hyphae.

By studying fungal growth, Vanderscheuren hopes to fill gaps in the current CNAS research. CNAS researchers have shown that fungi compositions in forests are changing, but they are unsure of the mechanisms behind it. If Vanderscheuren’s work reveals that nitrogen-exposed fungi grow differently than her control group, this could provide a new direction for CNAS.

Vanderscheuren plans to present her research at the 2022 Mycological Society of America annual meeting. She’ll also share her work with the campus community through the CALS Undergraduate Research Symposium.

As she continues to spend long hours in the lab tending her fungi, Vanderscheuren looks hopefully to a future with greater appreciation for the impact of these little organisms. “There is so much to learn about fungi and the human-induced changes to nutrient cycling,” she says. “The more people interested these subjects, the better.”