A tree's response to environmental changes: What can we expect over the next ...( The many environmental issues facing...)

The many environmental issues facing our society are prevalent in the media lately. Global warming, rainforest devastation, and endangered species have taken center stage. Our ecosystem is composed of a very delicate network of interactions among all species and the non-living environment. Predicting how each component of this complex system will respond to the many environmental changes sweeping the globe is a challenging problem today's scientists face.

A recent article by Dr. Abraham Miller-Rushing and his colleagues at Boston University published in the October issue of the American Journal of Botany (http://www.amjbot.org/cgi/content/full/96/10/1779) explores how increasing concentrations of atmospheric carbon dioxide (CO₂) may be affecting trees and, ultimately, affecting water and carbon cycles.

It is known that increasing concentrations of atmospheric CO₂ affect the physiology and behavior of many organisms, and in plants, changes to the pores (stomata) on the surface of leaves are one example of these effects. Stomata allow air (containing CO₂) to pass into the leaf while water vapor passes out of the leaf. Plants use carbon dioxide to produce sugars during the process of photosynthesis. With increasing concentrations of atmospheric CO₂, stomatal density decreases while rates of photosynthesis increase. The decrease in stomatal density results in decreased water loss through the leaves.

"These changes in stomatal behavior and water use efficiency can, in turn, have large impacts on plants and can alter ecosystem-scale water and carbon cycling," Miller-Rushing said. "For example, soil moisture, runoff, and river flows might increase and drought tolerance in individual plants might improve."

The relationship between atmospheric CO₂ concentrations and stomatal density is so constan
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