* Trees respire less carbon than expected as temperatures rise
* Study suggests trees may stoke warming less than feared
By Alister Doyle
OSLO, March 16 (Reuters) - 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 global warming.
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 Nature.
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 Reuters.
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)