How Seeds Spread

A Penn State biologist and collaborators have developed a new method for tracking seed movement and germination that will be useful for studying how plants adjust to global climate change. The technique may also help curtail the spread of invasive plants, according to Tomás Carlo, assistant professor of biology.

The team's new approach, Carlo says, is based on an isotope tracer method long used to investigate metabolic pathways in cells and track movement of fluids through soils. He and his team applied solutions of nitrogen-15, a stable, heavy isotope of nitrogen found in urea, to the leaves of several species of plants and trees. The plants soaked up the enriched solution and incorporated the nitrogen-15 into their tissues, including the seeds that they would later produce.

Once the plant's seeds had been dispersed by birds, Carlo collected the seeds and seedlings, ground them up, and placed a tiny sub-sample into a mass spectrometer to measure the amount of nitrogen-15. "We found that all of the seeds and seedlings that came from the plant that we had treated had strong nitrogen-15 signatures," he reports. The team also found that they could track seed dispersal for up to three individuals at a time by spraying parent plants with different concentrations of urea.

"Organisms will have to migrate to cope with climate change," says Carlo. "So there is interest in estimating patterns of seed dispersal, especially in fragmented and highly altered landscapes. Our technique could help scientists to understand the likelihood that a particular plant species will be successful at shifting its range. It could also help land managers control invasive species. By understanding how these species spread, we can attempt to prevent them from getting to places where they are predicted to go."

Tomas A. Carlo, Ph.D., is assistant professor of biology in the Eberly College of Science. His collaborators for this study were Joshua Tewksbury of the University of Washington, and Carlos Martínez del Río of the University of Wyoming. The team's results appeared in the December 2009 issue of the journal Ecology, and the research was supported by the National Science Foundation.

Last Updated June 29, 2010