The most significant factor in determining whether a plant will become invasive may be the size of its genome, says an international research team that studies the invasive reed phragmites.

Laura Meyerson, URI professor of natural resources science, reports that “our results are crystal clear. Small genomes are the most important factor in determining invasiveness, at least for Phragmites, but likely for many other species as well.”

The team—which also included Petr Pyek and the late Jan Suda from the Institute of Botany at The Czech Academy of Sciences—screened 900 populations of phragmites from around the world and chose 100 to evaluate. The researchers grew those plants in a common garden in the Czech Republic, where they exposed them to the same environmental conditions and regularly measured a wide variety of traits, from nutrient content and leaf toughness to plant chemistry and susceptibility to herbivores. Their results were published January in the journal Ecology.

While all of the plants studied were of the same species, Phragmites australis, their genome size varied from population to population.

Meyerson says the results suggest that plants with large genomes can grow only in limited locations. The Gulf of Mexico lineage of phragmites, for instance, which has a large genome, has been unable to move out of the Gulf region, whereas the phragmites native to Europe, which has a small genome, is highly invasive throughout North America.

“Smaller genomes are more nimble,” she says. “They can grow in variable environments and at almost all latitudes.”

The findings of the research team raise the question of why plants with small genomes are more likely to become invasive. She thinks they have the answer.

“The main theoretical reason has to do with minimum generation time,” she explains. “The idea is that a smaller genome can be replicated more quickly than a larger genome. So if a plant is in a stressful environment, it can be replicated more quickly than if it had a larger genome. It needs fewer resources and can use its resources quickly to reproduce before its luck runs out.”

On the other hand, “a smaller genome also means that it may lose genes that are potentially beneficial,” adds Pyek. “So there may be a trade-off.”

Scientists use flow cytometry, a simple and inexpensive technology, to measure the size of a plant’s genome. The speed and simplicity of the process provides numerous applications for the results of the research, the team suggests. Border security officers, for instance, could quickly screen plants for genome size before they are imported into a country.

“It gives us a cheap tool to measure their invasive potential,” says Meyerson.

The test could also be used to prioritize the management of existing invasive populations of common reeds and other plants with the same genome size characteristics. “Land managers could screen invasive populations for genome size to help them allocate resources more effectively,” Meyerson says. “By determining whether a population has a particularly small genome size, they will know that a particular plant might be more aggressive and should be targeted for removal.”

Meyerson is also conducting experiments at URI to determine how environmental variables like salinity and temperature interact with plants of different genome sizes, and how plant chemistry is affected by genome size.