Effects of Elevated Carbon Dioxide, Water, and Nutrients on Photosynthesis, Stomatal Conductance, and Total Chlorophyll Content of Young Loblolly Pine (Pinus taeda L.) Trees

Abstract

Global atmospheric carbon dioxide concentration, presently at about 350 μl 1-1, is expected to continue to increase in the future (Lindzen, 1993) and may double by the end of the next century (Gates, 1983; Keeling et al., 1989; Houghton and Woodwell, 1989). Higher levels of carbon dioxide may increase the growth rate of trees and the productivity of forests (Teskey, 1995). At the present-day, ambient carbon dioxide concentration and under optimal conditions, the photosynthesis of plants is limited by the supply of carbon dioxide (Arp, 1991). Numerous studies have shown increased plant growth in elevated levels of carbon dioxide (Higginbotham et al., 1983, 1985; Stewart and Hoddinott, 1993; Gunderson et al., 1993), but these studies have used potted seedlings, optimum levels of resources (including water and nutrients), and short-term exposure to higher carbon dioxide concentrations. Because seedlings differ from older trees both physiologically and morphologically (Cregg et al., 1989), it is unknown how much carbon gain in trees will be affected by long-term exposures to elevated carbon dioxide levels under field conditions in which water and nutrient availability may limit growth.