Invasive Roly-polys Might Actually Help The Soil, Study Reveals

Katarina Juhaszova's original research, focusing on the effect that several species of isopods have on soil nutrients, has been funded with support from a Johns Hopkins Provost's Undergraduate Research Award (PURA). As one of 45 PURA winners this academic year, Juhaszova presented the results of her research at an awards ceremony held at Johns Hopkins on March 10.

Since 1993, about 40 students each year have received PURA grants of up to $3,000 to conduct original research, some results of which have been published in professional journals. The awards, funded through donations from the Hodson Trust, are an important part of the university's commitment to undergraduate research.

Knowing that isopods are not native to the Mid- Atlantic region (they were brought to America during European colonization), Juhaszova wondered what effect — if any — the small creatures were having on the nutritional composition of forest soil, which, over time, can lead to changes in the forests' plant and animal composition.

Working under the guidance of sponsor Katalin Szlavecz, associate scientist in the Morton K. Blaustein Department of Earth and Planetary Sciences, Juhaszova ventured into local forests, where she studied the impact that six species of isopods had on the rate at which leaf litter (which provides food for the creatures) disappeared. In laboratory experiments, she also examined how the isopods' feeding activity alters the soil's organic matter content and nitrogen availability.

What she learned surprised her.

"We found that instead of depleting the nutrients in the soil, which is what has happened with some invasive species, the isopods actually are having the opposite effect," Juhaszova said. "Their droppings produce a good source of carbon for the microbes there, promoting their growth."

Szlavecz calls her student's results "certainly interesting and worth investigating further."

"We know that a sudden influx of non-native detritivores (creatures that eat leaf litter and other detritus) is likely to change the nutrient availability of forests over time, and not always for the better," Szlavecz said. "That's the case with earthworms; though they promote the decomposition of organic nitrogen, they do it at a rate that is so high that eventually nitrogen can be lost from the forests. What we are getting from Katy's research is that isopods have the opposite effect. Though it would be far-fetched and pompous for us to draw some big conclusions regarding the whole ecosystem level process based on Katy's data, it certainly is worth further scrutiny."