As CO2 rises trees can ‘rewire’ to increase absorption
Root intelligence: How old trees learn to suck more CO2 from the air.
New research finds that centuries-old oaks can dynamically rewire how they absorb nutrients—suggesting forests may be more resilient allies in the climate fight than once believed.
July 16, 2025 in Anthropocene
While greenhouse gas pollution has lots of down sides, there’s one potential benefit: Carbon dioxide is food for plants. As CO2 levels rise in the atmosphere, some plants are expected to enjoy a growth boom.
Not only does that mean more vegetation. It could also help counter some of carbon pollution as plants pull it from the air and store it in their roots, leaves and trunks.
But the arithmetic isn’t as simple as more carbon means more green. Among other things, just as people can’t live only on energy-rich carbohydrates, plants need nutrients such as nitrogen and iron to grow. If there is more carbon “food” floating in the air, will plants, especially long-lived trees, be able to use it?
A forest of oak trees dating back to the mid-19th century in the United Kingdom holds some answers. There, scientists have witnessed the adaptive genius of trees. The results, spelled out this week in the Proceedings of the National Academy of Sciences, suggest that at least some species of trees, even old ones, are equipped with tools that will enable them to capitalize on the carbon surplus. That’s good news both for the trees and for the climate.
“These findings indicate that trees are more agile in optimizing growth than previously thought and will continue to be agile under higher CO2 atmospheres as long as soil nutrient supplies are sustained,” said Michaela Reay, a postdoctoral researcher at the University of Bristol in the U.K. who took part in the study.
Some nutrients are critical to plant growth. It’s one reason why farmers mix fertilizer into soil and iron-rich whale poop can fuel algae blooms. Then there’s nitrogen, a building block for chlorophyll, a green pigment critical to photosynthesis, in which plants turn sunlight, water and CO2 into sugar and oxygen.
Trees have three main strategies for boosting their intake of such nutrients. They can grow more roots to reach more parts of the soil; release chemicals into the soil that spark a feeding frenzy among microbes that release nutrients; or foster more connections with symbiotic soil fungi that exchange carbon and nutrients with the tree.
To see whether older trees still have the flexibility to deploy any of these tools as greenhouse gas levels skyrocket, Reay and her colleagues turned to a 180-year-old forest in central England. Since 2017, scientists there have been pumping extra CO2 into the air surrounding groves of mature oak trees to mimic expected greenhouse gas levels in the middle of this century, in what’s known as the Birmingham Institute for Forest Research Free Air Carbon Dioxide Enrichment.
In the race to pull carbon from the air, did rocks just overtake trees?
In 2020 and 2021, scientist repeatedly collected samples of the trees and soil to see if trees fueled by these shots of CO2 acted differently from untreated trees when it came to hunting for nutrients.
It turns out these old oaks could, in fact, learn new tricks. Scientists found evidence that the gas-enriched trees used all three measures to boosting their access to nitrogen. Not only that, the plants varied their approach to coincide with conditions at different times of year, creating a complex dance rather than repeating the same movement over and over.
“Roots do not simply take up nutrients and water from soils but rather exhibit smart and dynamic choreography, which involves highly specialized tradeoffs with soil microbes via varied nutrient exploration strategies throughout the year,” said Reay.
Plant roots leaked more microbe-fueling carbon into the soil compared to trees living in current CO2 levels, especially during the peak summer growing season, when microbes were most active and trees had a surplus of carbon thanks to the longer days.
By contrast, in the fall, as trees were dropping their leaves, scientists witnessed more growth of symbiotic fungal networks, known as ectomycorrhiza. These fungi are expert at breaking down forest detritus such as fallen leaves and releasing nutrients. Trees in the higher-carbon world produced 3.6 times more biomass of these fungi.
Meanwhile, the carbon-enriched trees were also growing roots with more frequent branches, something that could enable the plants to delve into more soil pockets that might hold nutrients.
The emerging picture suggests that in places with adequate nutrient levels, “mature temperate forests could play a key role in the fight against climate change,” said Iain Hartley, an Exeter University scientist involved in the research.
But that partly depends on whether trees will eventually exhaust soil nutrients as they deploy all these tricks to scavenge more from the soil. That, said the scientists, is a subject of further research.
Reay, et. al. “Elevated CO2 alters relative belowground carbon investment for nutrient acquisition in a mature temperate forest.” Proceedings of the National Academy of Sciences. July 15, 2025.