Changes in CO2 Levels and Their Stress Effects on Photosynthetic Carbon Fixation

Abstract

As the global carbon dioxide concentration rises, we need to understand the combination of direct stress effects of this gas and the anticipated effects of climatic change, including drought, on the physiology and growth of all crops [1]. The current increase in the atmospheric carbon dioxide concentration along with predictions of possible future increases in global air temperatures have stimulated interest in the effects of CO2 and temperature on the growth and yield of food crops [2] 2 has been documented continuously since 1958 by Keeling et al. [3], and currently the concentration of CO2 in air is about 360 μL L . The concentration could increase to about 670–760 μL L 1 by the year 2075 mainly because of the burning of fossil fuels [4,5]. General circulation models predict that global warming will result from rising CO2 and other greenhouse gases [6–11]. The stress effects of rising CO2 and elevated temperatures on tropical plants have received less attention than the effects on temperate species [12]. Because both CO2 and temperature have large effects on plants, especially those with the C3 photosynthetic pathway, it is important to quantify the effects of these climatic variables on C3 food crops [10]. Concern over the well-documented increase in the concentration of carbon dioxide in the earth’s atmosphere has stimulated research on the response of plants to this aspect of global change. Much of this research has focused on the response of photosynthetic carbon dioxide fixation, because the process is often dramatically and directly affected by the carbon dioxide concentration, and it is of fundamental importance both to plant growth and to ecosystem carbon storage. The concentration of carbon dioxide in the atmo-