More CO2 in the atmosphere is driving mature oak trees to boost their photosynthesis, a process that scientists say could triple by 2050.

Researches from the University of Birmingham in Australia reported in the scientific journal Tree Physiology on experiments involving an old oak forest subjected to dramatically increased levels of carbon dioxide. Over the first three years of a ten-year project, the 175-year-old oaks clearly responded to the CO2 by consistently increasing their rate of photosynthesis.

This means the trees are capturing more carbon from the atmosphere than they normally would and releasing more oxygen. But scientists aren't sure yet where the additional captured carbon is going. They are measuring leaves, wood, roots, and soil to see where the carbon goes and how long it stays there.

The increase in photosynthesis was found to be greatest in strong sunlight. The overall balance of key nutrient elements carbon and nitrogen did not change in the leaves. According the report, that means keeping the carbon to nitrogen ratio constant suggests old trees have found ways of redirecting their elements, or found ways of bringing more nitrogen in from the soil to balance the carbon they are gaining from the air.

The research was carried out at the Free-Air CO2 Enrichment (FACE) facility of the Birmingham Institute of Forest Research (BIFoR) in close collaboration with colleagues from Western Sydney University who are running a similar experiment in old eucalyptus forest (EucFACE). BIFoR FACE and EucFACE are the world's two largest experiments investigating the effect of global change on nature.

"I'm really excited to contribute the first published science results to BIFoR FACE, an experiment of global importance,” said one of the researches, Anna Gardner, as reported in Science Daily. Gardner conducted measurements for the project. “It was hard work conducting measurements at the top of a 25 m oak day after day, but it was the only way to be sure how much extra the trees were photosynthesizing."

Scientists hope the research will better explain how trees sequester carbon. "It's a delight to see the first piece of the carbon jigsaw for BIFoR FACE fall into place,” said Professor Rob MacKenzie, founding Director of BIFoR. “We are sure now that the old trees are responding to future carbon dioxide levels. How the entire forest ecosystem responds is a much bigger question requiring many more detailed investigations. We are now pushing ahead with those investigations."