A recent study led by Penn State researchers reveals a concerning trend regarding the climate impact on tree CO2 absorption. The research highlights that trees, traditionally known for their ability to sequester carbon dioxide (CO2), are increasingly struggling in warmer, drier climates. This finding challenges the long-held view of trees as reliable carbon sinks in the fight against climate change.
Max Lloyd, assistant research professor of geosciences at Penn State, and the lead author of the study, emphasized the altered behavior of trees under these stressful conditions. In warmer and drier climates, trees are releasing CO2 back into the atmosphere at a higher rate than in cooler, wetter environments. This phenomenon, known as photorespiration, is up to two times higher in such climates, particularly where water is scarce. The study, which analyzed a global dataset of tree tissue, found that this increased rate of photorespiration begins when average daytime temperatures exceed about 68 degrees Fahrenheit. This raises concerns about the long-term efficacy of trees in sequestering carbon, especially as global temperatures continue to rise.
The climate impact on tree CO2 absorption has significant implications for how we understand the role of trees in mitigating climate change. Trees currently absorb about 25% of the CO2 emitted by human activities annually. However, this percentage is expected to decrease as the climate warms, with Lloyd noting that water scarcity could further exacerbate the situation. This suggests that trees might become less effective in drawing CO2 out of the atmosphere and assimilating the carbon necessary for cooling down the planet.
Further complicating the issue is the discovery that variations in the abundance of certain isotopes in wood, specifically methoxyl groups, can serve as tracers of photorespiration in trees. This groundbreaking revelation allows researchers to observe trends in photorespiration across various climates and conditions, using wood samples from an extensive archive at the University of California, Berkeley. These samples, collected in the 1930s and 1940s, are now being used to reconstruct historical forest CO2 absorption rates.
The study’s findings have opened new avenues for understanding the climate impact on tree CO2 absorption. By analyzing fossilized wood, the research team aims to unearth photorespiration rates from millions of years ago. This method will help test hypotheses about the changing influence of plant photorespiration on climate over geologic time. As Lloyd puts it, understanding these ancient cycles is crucial for predicting future climate impact on tree CO2 absorption and preparing for the challenges that lie ahead in our warming world.