Once the aggressive type of an invasive reed known as Phragmites australis settles into a marsh, it quickly spreads, forming a dense monoculture harmful to other species that live in the wetland. The grass flourishes particularly well in marshes polluted with nitrogen, which comes mostly from agricultural, suburban, or urban runoff, and under rising carbon dioxide levels expected under climate change.
This summer, Julian Garrison ’19 began tackling the complex question about how these two environmental conditions are facilitating the invasive plant’s growth. The more we understand about Phragmites‘ invasion ecology, Garrison explains, the better equipped we will be to stop its destructive takeovers.
Garrison’s work is linked to recent research by Bowdoin Associate Professor of Biology Vlad Douhovnikoff, who has looked into how the hardy grass is so successful at adapting to and overwhelming new environments. Douhovnikoff suspects that, unlike native phragmites, Phragmites australis may be using epigenetics to its advantage. That is, it can switch genes on and off in response to changing environmental conditions. Then, when it reproduces asexually, it can pass these learned responses to its clones.
Under the guidance of both Douhovnikoff and Professor of Biology Barry Logan, an expert in plant physiological ecology, Garrison has begun to add clues to help tell the story behind Phragmites‘ dominance.
Based on some promising results, Garrison is extending his research into a yearlong honors project. His project exemplifies the type of research possible by students in Ecology, Evolution, and Marine Biology, Bowdoin’s newest academic concentration. Garrison plans to add the concentration to his biology major.
Garrison is focusing on the effects that increased carbon dioxide and nitrogen have on Phragmites‘ stomata, which are tiny pores on leaves that control the intake of carbon dioxide and release of oxygen. The greater the gas exchange, the greater the photosynthesis that fuels plant growth.
Garrison’s research piggybacked on the work of a scientist who is running experiments on Phragmites australis in a Maryland marsh. Thomas Mozdzer, of Bryn Mawr College, has set up a study at the Smithsonian Environmental Research Center in Edgewater in which he is subjecting four groups of the reed to different growing conditions. One group is being dosed with higher amounts of carbon dioxide, another is being treated to more nitrogen (which in high amounts is a soil pollutant), a third is getting both more carbon dioxide and nitrogen, and the fourth group is serving as a control. Importantly, in each treatment group there are genetically identical Phragmites clones, allowing researchers to study the plasticity effect, or the epigenetic response, to the environmental conditions.
After receiving samples of leaves from all four of Mozdzer’s Phragmites groups this summer, Garrison used Bowdoin’s electron scanning microscope to count and measure each leaf’s stomata. Together, the number and length of a leaf’s stomata can indicate the plant’s stomatal conductance, or gas exchange rate.
So far, Garrison is seeing that the Phragmites subjected to higher carbon dioxide and nitrogen have greater stomatal conductance, suggesting they are adapting to their environment on the spot. “If you’re looking just at genetics, you would expect them all to grow the same,” Garrison said. “But they’re not. So there is some kind of plastic response to these treatments.”
Next, he will compare this data to another data set, the photosynthesis rates of the plants in the study. To his knowledge, Garrison says he’s the first to look at the link between Phragmites’ underlying stomatal morphology and its photosynthetic performance under global climate change.
His research could help reveal how Phragmites thrive in new habitats, pushing farther and deeper into marshes, even when the high salinity should prohibit its expansion. “Then hopefully down the road, a better understanding of its invasion ecology can help restore marshes or help people combat it better,” Garrison said.