Mature trees can increase the amount of carbon dioxide (CO2) they absorb, a new study shows, which is “good news” in the fight against climate change.
Scientists in Birmingham conducted a giant outdoor experiment on oaks in rural England that had reached ‘middle age’, meaning they stopped growing upwards.
The trees increased their rate of photosynthesis by up to a third when exposed to increased levels of CO2 from the air, they found.
The fact that mature trees are so abundant around the world could give humanity ‘extra room’ to combat climate change.
Forests are widely recognized as important ‘carbon sinks’ – ecosystems that can capture and store large amounts of CO2.
Mature oak trees will increase their photosynthesis rate by up to a third in response to the increased levels of CO2 expected by 2050, experts from the University of Birmingham report. the researchers conducted a giant outdoor experiment on oak trees in Staffordshire (pictured)
HOW OLD IS THE OLDEST TREE?
The oldest trees on Earth have stood for nearly five millennia.
The oldest individual tree in the world is thought to be in the US, where a Great Basin pine tree in California’s White Mountains lived to be more than 5,000 years old.
A Fortingall Yew in Perthshire, Scotland, is believed to be the oldest tree in the UK, estimated to be between 2,000 and 3,000 years old, according to the Woodland Trust.
Long-lived trees have received special attention in aging research, as “a kind of mirror” in which we could potentially see ourselves reflected in our efforts to achieve longer lifespans.
The research was conducted on trees in Staffordshire at the Birmingham Institute of Forest Research (BIFoR) and published in: Tree physiology.
“We are now confident that the old trees will respond to future CO2 levels,” says Professor Rob MacKenzie, founder of BIfoR.
“How the entire forest ecosystem responds is a much bigger question that requires much more detailed research. We are now continuing those investigations.’
For the study, the 175-year-old oak trees in Staffordshire were bathed in air containing 37 percent more CO2 than normal — similar to levels expected in the air by 2050.
The experiments were based on Free-Air Carbon Dioxide Enrichment (FACE), a research facility in mature, unmanaged forest about an hour’s drive from the University of Birmingham’s main campus.
FACE consists of a network of tall pylons, which somewhat resemble high-voltage pylons, that release CO2 to the surrounding trees.
Leaves at the top of the canopy were then analyzed for their photosynthetic response, by researchers in harnesses up to 75 feet above the ground.
During the first three years of their 10-year project, the researchers found that the oaks increased their photosynthesis rate by as much as 33 percent.
Researchers are now measuring leaves, wood, roots and soil to find out where the extra captured carbon ends up and how long it stays locked up in the forest.
For the study, the 175-year-old oak trees in Staffordshire were bathed in air containing 37 percent more CO2 than normal – similar to levels expected in the air by 2050
Located in rural Staffordshire, FACE consists of a network of tall masts emitting CO2 into the surrounding trees
WHAT IS A CARBON SINK?
A carbon sink is anything that takes up more carbon from the atmosphere than it gives off.
The ocean, atmosphere, soil and forests are the world’s largest carbon sinks.
In contrast, ‘a carbon source’ is anything that releases more carbon into the atmosphere than it takes up, for example the burning of fossil fuels or volcanic eruptions.
Professor Mackenzie said the study was at an early stage but so far it’s ‘good news’, he told the times, in part because mature trees make up most of the world’s forests.
Forests absorb 25 to 30 percent of the extra CO2 released into the air through human activity, and can maintain a similar percentage as levels rise.
“Maybe the world’s forest will continue to deliver that reduction of carbon and give us a few more years of room in our climate mitigation,” said Professor Mackenzie.
“That’s about as much as we can hope for — the problem isn’t going away.”
Interestingly, the overall balance of key nutritional elements carbon and nitrogen did not change in the leaves.
Keeping the carbon-nitrogen ratio constant suggests that the ancient trees may have found ways to redirect their elements, or found ways to take more nitrogen from the soil to balance the carbon they take from the air.
The study was conducted in collaboration with colleagues from Western Sydney University who are conducting a similar experiment in the ancient eucalyptus forest (EucFACE) northwest of the Australian city.
The University of Birmingham has set up a Free-Air Carbon Dioxide Enrichment (FACE) experiment in mature, unmanaged, temperate forests. It is located in its own grounds in Staffordshire, approximately 1 hour’s drive from the main university campus
“Earlier work at EucFACE measured photosynthesis increased by up to one-fifth in elevated carbon dioxide,” said study author Professor David Ellsworth at Western Sydney University.
‘So we now know how old forest responds to the warm-temperate climate we have here in Sydney, and the mild temperate climate of the northern mid-latitudes where Birmingham is.
‘We did not find any additional growth in higher CO2 at EucFACE and it remains to be seen whether this will also be the case for BIFOR.’
An increase in atmospheric CO2 — a key ingredient for photosynthesis — can trigger growth spurts for tree species, but too much could have negative consequences, a previous study suggests.
HOW DOES PHOTOSYNTHESIS WORK?
Photosynthesis is a chemical process used by plants to convert light energy and carbon dioxide into glucose for the plant to grow, releasing oxygen.
The leaves of green plants contain hundreds of pigment molecules (chlorophyll and others) that absorb light at specific wavelengths.
When light of the correct wavelength hits one of these molecules, the molecule enters an excited state — and energy from this excited state is shuttled down a chain of pigment molecules until it reaches a specific type of chlorophyll in the photosynthetic reaction center.
Schematic showing how photosynthesis works. One of the most important steps in photosynthesis is the splitting of water to release hydrogen and oxygen atoms, forming glucose sugar so that the plant can grow and release oxygen as a byproduct.
Here, energy is used to drive the charge separation process necessary for photosynthesis to proceed.
The electron ‘hole’ that remains in the chlorophyll molecule is used to ‘split’ water into oxygen.
Hydrogen ions formed during the water splitting process are eventually used to convert carbon dioxide into glucose energy, which the plant used to grow.