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Photorespiration is a process in plants that occurs during photosynthesis, where they consume oxygen (O2) and release carbon dioxide (CO2) instead of the usual reverse process. The extent and variation of photorespiration in the current environment is not fully understood.
Trees’ ability to effectively absorb and store carbon dioxide (CO2), a crucial mechanism for offsetting human carbon emissions, is being hampered in hotter, drier climates, according to a recent study led by Penn State researchers.
Max Lloyd, assistant professor of geosciences at Penn State, said: “We found that trees in warmer, drier climates essentially cough instead of breathe. “They send CO2 back into the atmosphere much more than trees do in colder, wetter conditions.”
Photosynthesis allows trees to extract carbon dioxide (CO2) from the atmosphere, which contributes to new growth. However, under stressful conditions, trees undergo photorespiration, releasing CO2 into the atmosphere. A global analysis of tree tissue by the research team revealed that the rate of photorespiration increases up to two-fold in warmer climates, mainly when water is scarce. The threshold for this response in subtropical climates begins to be crossed when average daytime temperatures exceed approximately 68 degrees Fahrenheit and intensifies with further increases in temperature.
These findings challenge widely held beliefs about the role of plants in carbon sequestration and provide new insights into how plants could adapt to climate change. Crucially, as the climate warms, the study suggests that plants may become less efficient at removing CO2 from the atmosphere and assimilating needed carbon, which could hinder their role in cooling the planet.
Lloyd said, “We have unbalanced this essential cycle. Plants and climate are inextricably linked. The greatest absorption of CO2 from our atmosphere is produced by photosynthesizing organisms. “It is a big factor in the composition of the atmosphere, meaning that small changes have a big impact.”
Currently, plants absorb approximately 25% of the CO2 emitted annually by human activities, according to the US Department of Energy. However, this percentage is likely to decrease in the future as the climate warms, especially in scenarios where water becomes more scarce, according to the study led by Lloyd. A warming climate poses a trade-off because, although rising CO2 levels theoretically benefit plants, rising temperatures can hamper their ability to effectively reduce CO2.
In the research, scientists identified that the variation in the abundance of specific isotopes in a component of wood called methoxyl groups serves as a marker of photorespiration in trees. Isotopes are analogous to different types of atoms. By studying the methoxyl “flavor” of isotopes in wood samples from various trees around the world, the researchers observed trends in photorespiration. The samples were obtained from a collection at the University of California, Berkeley, which contains wood samples dating to the 1930s and 40s, providing valuable historical data for the study.
lloyd saying, “The database was originally used to train foresters on how to identify trees from different places around the world, so we reused it to reconstruct these forests and see how well they were absorbing CO2.”
Traditionally, measuring photorespiration rates required real-time assessments of live plants or well-preserved dead specimens that retained structural carbohydrates. This limitation made it nearly impossible to study the rate at which plants sequester carbon on a large scale or to examine historical rates of photorespiration.
However, the recently validated method of observing photorespiration rates using wood provides a tool for researchers to predict how efficiently trees could absorb carbon in the future and how they performed in past climates.
As carbon dioxide levels in the atmosphere rapidly rise to unprecedented levels in the past 3.6 million years, according to the National Oceanic and Atmospheric Administration, understanding the historical context becomes crucial.
The research team plans to extend their investigations into the ancient past by studying fossilized wood, potentially dating back tens of millions of years. This approach will allow researchers to test existing hypotheses about the changing impact of plant photorespiration on climate over geological time scales.
Magazine reference:
- Max K. Lloyd, Rebekah A. Stein, Daniel E. Ibarra and Daniel A. Stolper. Isotopic agglomeration in wood as an indicator of photorespiration in trees. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.2306736120