What if carbon dioxide levels 50 million years ago were actually higher then they are today? Would that tell us anything about the gas’s role in global climate change? Dana Royer, Professor of Earth and Environmental Studies, has been using various techniques to analyze the leaves of fossil and modern plant species, hoping to answer these questions.
According to Royer, teeth or ridges along plant edges provide information on temperatures, and leaf pores may yield new data on the relationship between carbon dioxide levels and global temperatures.

“I explore how plants can be used to reconstruct ancient environments, and the (paleo-) physiological underpinnings behind these plant-environment relationships,” Royer writes on his website. “I also compile Phanerozoic carbon dioxide records and investigate the strength of carbon dioxide-temperature coupling over multi-million-year timescales.”
The first project Royer is working on uses leaf edges to estimate temperature and rainfall by comparing leaf characteristics. Teeth facilitate processes critical to plant growth, which means the more teeth, the cooler the environment.

In fact, in a recent research project using Rhode Island Red Maples, Royer found that Red Maples native to one region have the plasticity to change leaf shape to adapt to new climates. After two years of growth in Florida, the Red Maples had fewer teeth than seeds planted at the same time in the colder climate of Rhode Island.

“Going into the past does give us some analogs to play with,” Royer said in regard to his research. “It may give us some clues as to what will happen in one hundred years.”
In a second project on leaves, this time studying their surface pores, Royer found that carbon dioxide levels 50 million years ago were very similar to what they are today, despite a significantly warmer climate.

“Obviously there were other factors back then that were the main contributors, like methane,” Royer said.

Funding from the National Science foundation has allowed Royer to enlist the help of six undergraduate students and a post-doctorial faculty member. According to one of those enlisted, Mike Moody ’09, he and the other students got to do more than just sit in a lab.
“Over the summer, the students working for Dana, including myself, were given the awesome opportunity to go to the Smithsonian in D.C. as ‘visiting paleobotanists,’ where we photographed a large collection of leaves,” Moody said.

The next few months of the students’ work consisted of prepping these leaf photos and then analyzing them in a program called ImageJ. They used this analysis to create an inventory of each leaf’s number of stomata, which are pores in the surface of leaves and other plant parts that plants use to interchange water and gases. Finally, the data from the photos of fossil plants were compared to analogous data for modern species.

“We can see how the living plant responds to different carbon dioxide levels,” Royer said. “Assuming that the fossils of these plants reacted in the same way, we can compare the density of the stomata to reconstruct the carbon dioxide levels.”

Last year, Gabriela Doria, a graduate student working with Royer, presented findings from similar research at the Eighth International Organization of Paleobotany and Palynology Conference in Bonn, Germany. Doria’s work, which she will complete this spring, focuses on the coniferous Metasequoia, a species present both today and 40 million years ago, when the earth was fluctuating between warm and cool periods. According to Doria, her work involves extensive measurements of fossil plants as well as experiments with living plants.
“[My findings] are an important addition to studies focused on linking stomata characters to aspects of climate and ecology,” she said.

While many studies have been done on carbon dioxide levels in the past, present and future, Professor Royer’s study is the first time that stomata – leaf pores – have been used. According to Royer, these stomata, while small, may be able to play a huge role in understanding climate change.

“The research that I’m doing with these students may help us to understand what could happen in the future.”