Studies show rising ozone levels threaten trees, crops

The Capital Times (Madison, Wisconsin): People have a hard time breathing when ozone levels are high. So do plants. "It is very similar to people with asthma," said David Karnosky, a forestry professor at Michigan Tech University in charge of a long-running experiment near Rhinelander in northern Wisconsin where some trees get extra doses of ozone and others do not. "This is the canary in the coal mine," Karnosky warned, explaining that the levels of ozone the trees in the experiment are experiencing are comparable to the levels that could exist in northern Wisconsin by 2050.

If that happens, the consequences are potentially serious for both plants and people. Asthmatic plants grow more slowly, which is bad news for crop production, and affected trees and plants also consume less carbon dioxide, which leaves more of it in the air where it traps heat on the planet and may harm people if breathed in high concentrations.

…But plants can't just pick up their roots and go inside. So they close the little mouths -- called stomata -- on their leaves that take in carbon dioxide. Though carbon dioxide in high amounts is bad for people, it is vital for plants, which use it with light and water to produce food and oxygen. If they don't get enough carbon dioxide, they don't grow as much as they should. "The ones that close up are less affected by the ozone because they take in less, but they also take in less carbon dioxide, so it reduces photosynthesis," said Thomas Sharkey, a former University of Wisconsin-Madison botany professor who is now a professor at Michigan State University and has done research at the Rhinelander site.

But the ozone that does get in through the stomata has the same effect that it would have on a human being running on a high ozone day, said Massachusetts Institute of Technology researcher John Reilly, who has studied ozone's effects on crops as well as trees. "That damages human lungs, and in the same sense, plants are damaged." Almost 5,000 trees planted 10 years ago at the 40-acre research site on U.S. Forest Service land near Rhinelander have been tested via a complex system of pipes and valves that apply carbon dioxide to three "rings" of trees, ozone to three other rings and a combination of the two gases to another three rings. A control ring group just receives the local air.

Trees that got those extra shots of ozone have only three-fourths as much growth and yield as those that did not receive the pollutant, Karnosky said. "It knocks your eyes right out," Sharkey added....

Leaf with veins, photo by Jon Sullivan, who has generously released it into the public domain via Wikimedia Commons. Thank you, Jon