Trees are struggling to sequester heat-trapping carbon dioxide (CO2) in warmer, drier climates, meaning that they may no longer serve as a solution for offsetting humanity’s carbon footprint as the planet continues to warm, according to a new study led by Penn State researchers.
“We found that trees in warmer, drier climates are essentially coughing instead of breathing,” said Max Lloyd assistant research professor of geosciences at Penn State and lead author on the study recently published in Proceedings of the National Academy of Sciences. “They are sending CO2 right back into the atmosphere far more than trees in cooler, wetter conditions.”
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In the study, the researchers discovered that variation in the abundance of certain isotopes of a part of wood called methoxyl groups serves as a tracer of photorespiration in trees. You can think of isotopes as varieties of atoms, Lloyd explained. Just as you might have vanilla and chocolate versions of ice cream, atoms can have different isotopes with their own unique “flavors” due to variations in their mass. The team studied levels of the methoxyl “flavor” of isotope in wood samples from about thirty specimens of trees from a variety of climates and conditions throughout the world to observe trends in photorespiration. The specimens came from an archive at the National Oceanic and Atmospheric Administration. But that period is relatively recent in geologic time, Lloyd explained.
The team will now work to unearth photorespiration rates in the ancient past, up to tens of millions of years ago, using fossilized wood. The methods will allow researchers to explicitly test existing hypotheses regarding the changing influence of plant photorespiration on climate over geologic time.
“I’m a geologist, I work in the past,” Lloyd said. “So, if we’re interested in these big questions about how this cycle worked when the climate was very different than today, we can’t use living plants. We may have to go back millions of years to better understand what our future might look like.”
Reference: “Isotopic clumping in wood as a proxy for photorespiration in trees” by Max K. Lloyd, Rebekah A. Stein, Daniel E. Ibarra, Richard S. Barclay, Scott L. Wing, David W. Stahle, Todd E. Dawson and Daniel A. Stolper, 6 November 2023, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2306736120
Other authors on the paper are Rebekah A. Stein, Daniel A. Stolper, Daniel E. Ibarra and Todd E. Dawson of the University of California, Berkeley; Richard S. Barclay and Scott L. Wing of the Smithsonian National Museum of Natural History and David W. Stahle of the University of Arkansas.
The work was funded in part by the Agouron Institute, the Heising-Simons Foundation, and the U.S. National Science Foundation.