TTrees are incredibly important in the battle against climate change. A mature tree can capture over 48 pounds of carbon in a year and hold onto it until the tree decays or burns. Currently, trees and plants absorb about 30 percent of the carbon dioxide humans release into the atmosphere each year through industry and activities. soak up However, the ability of trees to store carbon is at risk as the Earth continues to warm. This is because while trees absorb carbon dioxide through photosynthesis, they also release it back into the atmosphere through two processes that are sensitive to rising temperatures. The challenge has been accurately predicting how this balance will shift as the climate and atmosphere change.
A recent study published in the Proceedings of the National Academy of Sciences reveals that when daily temperatures surpass 68 degrees Fahrenheit and during drought conditions, trees may release significantly more carbon dioxide into the atmosphere through a process called photorespiration. Current climate models have overlooked this important detail, according to Max Lloyd, the lead researcher of the study from Penn State University. release Photorespiration is a troublesome aspect of photosynthesis that occurs during the daytime and increases as temperatures rise and water availability decreases. Another process, called respiration, also releases CO2, primarily at night.
Now a new study in The research adds to concerns that trees may lose their ability to absorb carbon from the atmosphere as the climate heats up. An earlier study in Science Advances from 2021 found that by 2040, if temperatures continue to rise at the current pace, trees could only absorb 15 percent of human carbon emissions, half as much as they do today. This is due to the fact that as temperatures increase, trees’ nighttime carbon respiration rates rise while their ability to store carbon through photosynthesis declines. The Science Advances study, which examined 20 years of data from 250 sites, also identified a distinct temperature threshold above which forests transition from being carbon sinks to carbon sources. The new study in Proceedings of the National Academy of Sciences didn’t consider variations in photorespiration rates, which is what the Science Advances study describes.
If temperatures continue to rise at the current pace, trees could absorb half as much carbon as they do today.
To conduct their study, Lloyd and his colleagues developed a new chemical method for analyzing wood samples to determine the rate of photorespiration over a tree’s lifetime. Most other methods of calculating trees’ carbon intake and output, including the Science Advances study, rely on extrapolating from forest surveys, which provide only a snapshot over a short period of time. The new method of analyzing wood samples allows for the examination of historical climates on a larger scale. For the recent study, Lloyd analyzed historic wood samples from the Forest Products Laboratory of the University of California, Berkeley, some of which came from trees that originated as saplings in the 19th century when CO2 levels were different.
The PNAS concentrations were 65 percent of the levels at present. The researchers plan to examine petrified wood next, which might give us an idea of how photorespiration appeared in ancient climates. paper Howard Griffiths, who is a professor of plant physiology at the University of Cambridge, says it’s too early to determine the impact of photorespiration on the overall carbon budget. He states that the new method for calculating photorespiration rates needs to be validated through experiments on living tree tissue. Lloyd also agrees that experimental validation is a top priority for future research. This does not mean that Griffiths or other plant scientists are hopeful about the future: “The greater danger to forest carbon storage is the failure of water transport during drought,” he cautions. In hydraulic failure, which is the primary cause of death in old trees, a tree is no longer able to draw water from the ground and distribute it effectively, so it essentially dies of thirst. A decomposing tree releases the carbon it stored during its lifetime back into the atmosphere.“I agree that warmer and drier climates will potentially have negative effects on forests globally,” Lidong Mo adds. Mo is an expert on forest ecology from ETH Zurich and is the principal author of a
The from 2023 that discusses the types of forests with the greatest potential as carbon sinks to address climate change. Its primary conclusion was that, somewhat unexpectedly, the carbon absorption potential is greatest when a damaged forest—reduced by logging, fire, or drought—is allowed to recover naturally to maturity, as opposed to planting new trees on completely deforested land. It is a powerful reminder that trees are part of complex forest communities that do not behave uniformly. The terms “source” and “sink” can sometimes oversimplify this reality. Mo writes in an email, “Ultimately, nature and climate are intertwined. We require nature for the climate, and we require climate action for nature.” Lead image: Fahroni / Shutterstock A recent study suggests that climate change is disrupting the calculations. PNAS study describes.
To complete their study, Lloyd and his colleagues developed a new chemical method for analyzing wood samples that can determine the rate of photorespiration over a tree’s lifetime. Most other methods of calculating trees’ carbon intake and output—including the Science Advances work—rely on extrapolating from forest surveys, which provide only a snapshot over a short period of time. The new method of extrapolating from wood samples allows for analysis of historical climates and at scale.
For the new study, Lloyd dug into a treasure trove of historic wood samples preserved at the Forest Products Laboratory of the University of California, Berkeley. The wood came from trees felled in the 1930s and onward. In some cases, the trees he analyzed had started life as saplings in the 19th century, when CO levels were 65 percent of current concentrations. Next, the researchers plan to study fossilized wood, which could give us an idea of what photorespiration looked like in the climates of the distant past.
Howard Griffiths, professor of plant physiology at the University of Cambridge, says it’s too soon to say what impact photorespiration will have on the net carbon budget. The new method of calculating photorespiration rates needs to be experimentally validated on living tree tissue, he says. Lloyd agrees that experimental validation is a high priority for future work.
This doesn’t mean that Griffiths or other plant scientists are optimistic about the outlook: “The greater threat to forest carbon sequestration is hydraulic failure during drought,” he warns. In hydraulic failure, the primary cause of death in old trees, a tree can no longer suck water out of the ground and distribute it efficiently, so it effectively dies of thirst. A decomposing tree returns the carbon it sequestered during its lifetime back into the atmosphere.
“I agree that warmer and drier climates will potentially have adverse consequences on forests globally,” Lidong Mo adds. Mo is an expert on forest ecology from ETH Zürich and is the lead author of a Nature study from 2023 that weighs in on what kinds of forests hold the greatest potential as carbon sinks to combat climate change. Its main finding was that, perhaps counterintuitively, the carbon sink potential is greatest when you allow a damaged forest—depleted by logging, fire, or drought—to recover naturally to maturity, as opposed to planting new trees on land that has been completely deforested.
It is a potent reminder that trees belong to complex forest communities that don’t behave uniformly. The language of “source” and “sink” can sometimes flatten this reality. In an email, Mo writes, “In the end, nature and climate are interconnected. We need nature for climate and we need climate action for nature.”
Lead image: Fahroni / Shutterstock
