* Trees respire less carbon than expected as temperatures
* Study suggests trees may stoke warming less than feared
By Alister Doyle
OSLO, March 16 Trees can adapt to rising
temperatures and limit their natural emissions of greenhouse
gases, according to a study published on Wednesday that suggests
plants may have a smaller than expected role in stoking man-made
Trees, plants, people and other animals produce carbon
dioxide as a waste product from burning energy. As temperatures
rise, trees use more energy in respiration and emit more carbon
dioxide from their leaves.
"Plant respiration results in an annual flux of carbon
dioxide to the atmosphere that is six times as large as that due
to the emissions from fossil fuel burning, so changes in either
will impact future climate," scientists wrote in the journal
They found that 10 types of North American trees, in
artificially heated outdoor forest plots, adapted to higher
temperatures without drastically boosting the amount of carbon
produced by their leaves.
"Plants play less of a role than previously thought in
speeding up global warming through accelerated respiratory
carbon dioxide emissions," lead author Peter Reich of the
University of Minnesota told an online news conference.
"Given the number of plants on Earth this is a big deal," he
said of their role in the carbon cycle.
Apart from respiration, trees also absorb carbon dioxide to
build roots, branches and leaves, and release it when they rot
or burn. The study, and other experts, cautioned that the
research only focused on respiration by leaves.
Martijn Slot, of the Smithsonian Tropical Research Institute
in Panama who was not involved with the study, said respiration
was only part of the story.
"Global warming will also affect other plant properties --
e.g. photosynthesis, growth, mortality and reproduction -- and
we are a long way from a complete understanding of the effects
of rising temperatures on any of those processes," he told
Pierre Friedlingstein, a climate expert at Exeter University
who was also not involved, said the study drew too many
conclusions from leaf respiration. "I'm afraid this paper is not
a game changer," he wrote.
In the study, the scientists placed heaters, both above the
ground and in the soil, around trees and raised the average
temperatures by 3.4 degrees Celsius (6.8 Fahrenheit) above
normal in experiments that lasted from three to five years.
They found the trees raised their respiration by just 5
percent, against a predicted 23 percent with no acclimatisation,
indicating that trees can adapt to higher temperatures.
(Editing by Toby Davis)