Try this, it will help........
nytimes.com
New Studies Point to 'Carbon Starvation' as a Cause for Tree Mortality
Droughts can trigger insect invasions, or drying out of the plant. The 2005 piñon pine decline in the Southwest was initially attributed to bark beetles. But studies by Los Alamos National Laboratory last year revealed a mechanism tied to carbon starvation. The hypothesis suggests that trees die when they literally starve of carbon.
"If plants don't photosynthesize, they will die," said Nate McDowell, a researcher at Los Alamos and a strong proponent of the hypothesis. "The process is universal."
A drought-protective mechanism that causes self-starvation
During times of prolonged drought, trees close tiny pores called stomata on the surface of leaves through which they breathe. The response is triggered as the plant goes into emergency mode to conserve water and prevent evaporation. Since plants also inhale carbon dioxide through their leaves, closing the pores means that the plant starves itself by blocking the entry of carbon, an essential input for photosynthesis.
At the same time, they continue burning carbohydrates during respiration. At one point, the available store of food gets exhausted and the tree starts starving. It can then become vulnerable to insect attacks and other stressors, McDowell said.
"It is the law of conservation of energy which plants must obey," McDowell said. "An analogy is, if we stop earning money but keep spending it, eventually our bank account will hit zero."
Carbon starvation is a reasonable hypothesis when the tree is water-starved, according to scientists. Craig and Allen said the mechanism could act in concert with insect infestation during warmer weather, and drying out of trees to cause declines.
According to Anna Sala at the University of Montana Division of Biological Sciences, the hypothesis requires more evidence before being entirely accepted. She stressed the need to keep all research options open.
"Carbon starvation is very logical, but if it is accepted too easily, it can have a negative effect on the advancement of science," Sala said. |
