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item DUGAS, W.
item Polley, Herbert
item Mayeux Jr, Herman
item Johnson, Hyrum

Submitted to: Tree Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2001
Publication Date: 7/1/2001
Citation: Dugas, W.A., Polley, H.W., Mayeux, H.S., Johnson, H.B. 2001. Acclimation of whole-plant acacia farnesiana transpiration to CO2. Tree Physiology. 21: 771-773.

Interpretive Summary: Atmospheric concentrations of carbon dioxide are rising, primarily due to felling of forests and combustion of fossil fuels. Carbon dioxide levels are expected to be twice current levels at some time later in this century, and may eventually reach three times current levels. Changes in carbon dioxide levels have important effects on plants. For instance, increasing levels of carbon dioxide cause plants to decrease rates of water use, or transpiration, by partially closing the pores in leaves through which water is lost as vapor. Research reported here demonstrated that this response is substantial and can occur rapidly, at least in a glasshouse. Transpiration of one-year-old seedlings of a woody Acacia species from Texas decreased by about a third within one hour after plants grown at today's carbon dioxide level were exposed to air containing twice that level of carbon dioxide, and decreased another 15% when exposed to air with hthree times today's level. In addition, plants grown at the current carbo dioxide level always transpired twice as much water when exposed to different carbon dioxide levels than plants grown at high levels and then exposed to different levels. That is, the response of acacia plants to a change in carbon dioxide level depended on the carbon dioxide level at which they were grown. The research indicates that plant transpiration exhibits "acclimation" to rising carbon dioxide, which scientists define as a consistent difference in response to an environmental change associated with the conditions under which the plant developed.

Technical Abstract: Rising atmospheric carbon dioxide concentration ([CO2]) affects plant transpiration. The objectives of this study were to compare transpiration at current and elevated [CO2]s and to determine whether acclimation of transpiration to short-term changes in [CO2] could be observed. Daily whole-plant transpiration was measured from 26 Aug. through 18 Sept. 1993 using constant power stem flow gauges on a woody legume (Acacia smallii) grown for more than one year in 380 liter pots in greenhouse bays at [CO2]s of 385, 690, and 980 ppm. Stem flow measurements were validated using gravimetic transpiration measurements. The [CO2] in each bay was cycled among these three [CO2]s on selected days during the measurement period. In addition, the [CO2] was cycled in the bay with a growth [CO2] of 385 ppm between 385 and 690 ppm within the day on one day and between 385 and 980 ppm on another day. When measured at the growth [CO2], daily transpiration (per unit leaf area and normalized for daily radiation) decreased 37% when the [CO2] was increased from 385 to 690 ppm and another 15% when increased from 690 to 980 ppm. During the daily cycle of [CO2], transpiration from plants grown at 385 ppm was about two times greater than that for plants grown at 980 ppm when plants were temporarily at 385, 690, or 980 ppm. When [CO2] was elevated to 980 ppm within the day, transpiration from plants grown at 385 ppm within about one hour to rates measured when the [CO2] was maintained at 980 ppm thoughout the day.