Research seeks to determine how much extra carbon dioxide can trees absorb to reduce greenhouse emissions

The doubts expressed about this experiment are absurd.  They pretend that we don't know what plants use CO2 for.  But we know that perfectly well. They use it to build up theirown structure.  They turn it into wood etc.  So they will STORE in their own tissues the extra CO2 that they take in

The University of Oxford has erected towers in an old oak forest and then bathed the 175-year-old trees with carbon dioxide to mirror what CO2 levels will be like in 2050. 

When they measured the amount of photosynthesis that was occurring, it had increased by 30 per cent.

Trees absorb CO2 and give out oxygen, so their ability to manage rising CO2 levels is critical to human survival on a warming planet.

According to Professor Rob MacKenzie, it is a promising result, founding Director of Birmingham Institute of Forest Research (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."

The research was carried out at the Free-Air CO2 Enrichment (FACE) facility of the Birmingham Institute of Forest Research (BIFoR), and together with a similar project run by the Western Sydney University, they are the world's two largest experiments looking at the effect of climate change on nature.

Australian researcher Professor David Ellsworth thinks the results are significant. "The temperate zone is where a lot of the CO2 occurs, up in the northern hemisphere, and we need to know the trajectory of the uptake into the future to know what's going to happen with atmospheric CO2."

"They could be really important sinks for the CO2 into the future or perhaps they're already saturated; they take up more, but they don't store more."

When a similar experiment was conducted on a red gum forest in Australia in 2019, the trees photosynthesised just 20 per cent more CO2, so the UK result surprised Professor Ellsworth.

"That's quite a bit higher than our eucalyptus forests, and that was quite a surprise."

"Our eucalyptus trees have very high rates of photosynthesis … but they don't end up storing very much of that, so the CO2 goes back out into the atmosphere.

Researchers in the UK are now looking at the leaves, wood, roots, and soil in their old oak forest to find out where the extra carbon captured ends up and for how long it stays locked up.

"The CO2 being taken up by the trees is a good thing, but if it is taken up by the trees, metabolised internally and then shot back out to the atmosphere, then there really isn't any net storage or net savings of CO2 in that system," Professor Ellsworth said.

Other results from the UK experiment show that the increase in photosynthesis was greatest in strong sunlight.

The overall balance of key nutrient elements carbon and nitrogen did not change in the leaves, and 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 research will help governments work on how to respond to climate change and how to manage the existing forests.

"Old trees account for the vast majority of the land base in Australia, so we need to understand how much are they taking up now, how much are they going to take up in the future.

"Not only are they taking up CO2 in the present day, but if we cut them down, something happens with all the carbon that's been bound up in them, and we don't want that to go back up in the atmosphere."

https://www.abc.net.au/news/rural/2021-10-10/oak-trees-soak-up-extra-carbon-emissions/100527448