Washington: Scientists have reported that as carbon dioxide levels have risen during the last 150 years, the density of pores that allow plants to breathe has dwindled by 34 percent, restricting the amount of water vapor the plants release to the atmosphere.
The research team from Indiana University Bloomington and Utrecht University in the Netherlands gathered their data from a diversity of plant species in Florida, including living individuals as well as samples extracted from herbarium collections and peat formations 100 to 150 years old.
"The increase in carbon dioxide by about 100 parts per million has had a profound effect on the number of stomata and, to a lesser extent, the size of the stomata," said Research Scientist in Biology and Professor Emeritus in Geology David Dilcher, the two papers`` sole American coauthor.
"Our analysis of that structural change shows there``s been a huge reduction in the release of water to the atmosphere."
Most plants use a pore-like structure called stomata (singular: stoma) on the undersides of leaves to absorb carbon dioxide from the air. Stomata also allow plants to "transpire" water, or release water to the atmosphere.
If there are fewer stomata, or the stomata are closed more of the day, gas exchange will be limited -- transpiration included.
"The carbon cycle is important, but so is the water cycle," Dilcher said.
"If transpiration decreases, there may be more moisture in the ground at first, but if there``s less rainfall that may mean there``s less moisture in ground eventually. This is part of the hyrdrogeologic cycle. Land plants are a crucially important part of it."
The study has been published in the upcoming issue of the Proceedings of the National Academy of Sciences (now online).