The ability of forests to absorb carbon dioxide from the atmosphere has been overrated, according to a new study by US and Australian scientists.

Forest-smallerThe ability of forests to absorb carbon dioxide from the atmosphere has been overrated, according to a new study by US and Australian scientists.

In a paper appearing this week in the Proceedings of the National Academy of Sciences, Dr Richard Norby of the Oak Ridge National Laboratory, Tennessee, and colleagues argue that an essential element, nitrogen, had previously not been adequately factored into the equation.

One of the co-authors of the paper, Dr Belinda Medlyn of the Department of Biological Sciences at Macquarie University in Sydney, says the current study is a continuation of earlier research investigating Liquidambar styraciflua trees that were exposed to carbon dioxide (CO2) concentrations about 25 per cent higher than current levels.

Dr Medlyn says the study into how the trees would respond to increased concentrations of CO2 confirmed their hypothesis that there would be a point at which nutrient availability, specifically nitrogen availability, would limit the CO2 uptake of plants.

“The exciting thing about these results is that after another five years we found that the CO2 response is not actually maintained. What that’s telling us is that plants have the capacity to go looking for extra nutrition in the soil and that’s what’s happened here,” she said.

“They put down deeper roots, they found extra nutrition in the soil and that’s kept them going for a while, and certainly longer than we thought they would be able to. But after ten years they’ve finally run out of nitrogen.

“The implication of that for the broader landscapes is that particularly in nutrient poor soils, the rising CO2 concentration in the atmosphere is probably not going to be as beneficial to plants as we’ve been hoping.”

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Source: Carl Holm | ABC Science Online
Photo: Simon Cullen | ABC News — Forests acting as carbon sinks are not the quick fix solution some had hoped for.