From: Sara Coelho, Planet Earth Online
Published May 5, 2011 08:40 AM

Araucarias gauge ancient levels of carbon dioxide

Knowing the concentration of carbon dioxide (CO2) in the atmosphere today is easy — you just go outside and measure it — but gauging levels of CO2 from millions of years ago is not so simple. Now scientists have found how araucarias can help to solve the problem.

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One way of telling how much carbon dioxide was in the atmosphere in the past is by counting pores (or stomata) in leaves — the tiny openings plants use to absorb CO2 and lose water. It may seem far-fetched, but plants tend to decrease the number of pores when the atmospheric CO2 is increased.

The catch is that most plant species stop decreasing the amount of stomata if the CO2 concentration is above 400 parts per million. This is known as the ceiling response and 'really limits the effectiveness of the technique during periods of high concentrations of carbon dioxide, which are obviously the periods we are most interested in to compare with current rising CO2,' says Haworth.

And this is where araucarias come in handy.

Araucarias nowadays are not very common, but 200 million years ago they represented a large chunk of the world's forests. These trees evolved in a period when the concentration of CO2 in the atmosphere was a lot higher than it is today and for that reason araucarias are good candidates to gauge the levels of CO2 in the atmosphere during the age of dinosaurs.

Article continues: http://planetearth.nerc.ac.uk/news/story.aspx?id=967

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