Oak trees increase photosynthesis in response to CO2

Mature oak trees increase their rate of photosynthesis in response to increased CO2 levels, according to a new study published in Tree Physiology. 

The results are the first to emerge from a new outdoor experiment led by the University of Birmingham in which an old oak forest is bathed in elevated CO2 levels. 

Over the first three years of the ten-year project, the 175-year-old oaks clearly responded to the CO2 by consistently increasing their rate of photosynthesis. 

The increase in photosynthesis was greatest in strong sunlight. 

The researchers predict that the oak trees will increase their rate of photosynthesis by up to a third in response to the raise CO2 levels expected to be the world average by about 2050.

green leaf tree under blue sky

Keeping the carbon to nitrogen ratio constant suggests that the 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 researchers are now measuring leaves, wood, roots, and soil to find out where the extra carbon captured ends up and for how long it stays locked up in the forest.

Anna Gardner, who carried out the measurements, said: ‘I’m really excited to contribute the first published science results to BIFoR FACE, an experiment of global importance. 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 photosynthesising.’

Professor David Ellsworth, EucFACE lead scientist, added: ‘Previous work at EucFACE measured photosynthesis increased by up to a fifth in increased carbon dioxide. So, we now know how the old forest responds in the warm-temperate climate that we have here in Sydney and the mild temperate climate of the northern middle latitudes where Birmingham sits. At EucFACE we found no additional growth in higher CO2, and it remains to be seen if that will be the case for BIFOR as well.’

Photo by niko photos


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