3
Crop Plant Responses to Rising CO 2 and Climate
Change
Joseph C. V. Vu and Leon Hartwell Allen, Jr.
U.S. Department of Agriculture–Agricultural Research Service, and University of Florida, Gainesville, Florida
Maria Gallo-Meagher
University of Florida, Gainesville, Florida
35I. INTRODUCTION
The earth’s atmospheric carbon dioxide concentration ([CO 2 ]) has fluctuated between 170 and 300 ppm
over the past 160,000 years. However, since the start of the industrial revolution in Western Europe
(1750–1800), atmospheric [CO 2 ] has increased from 280 to approximately 365 ppm at present [1,2]. The
future [CO 2 ] depends on the degree to which CO 2 emissions are controlled. However, with the rapid in-
crease in world population and economic activity, a doubling of the present atmospheric [CO 2 ], assum-
ing a mean annual increase rate of 1.5 ppm, which was observed over the decade 1984–1993 [2], could
be expected before the end of the 21st century [1,3,4]. A rise in atmospheric [CO 2 ] may have important
effects on global climate. As CO 2 is responsible for 61% of global warming [5], a doubling of the atmo-
spheric [CO 2 ] and a rise in other so-called greenhouse gases (methane, nitrous oxide, chlorofluorocar-
bons) would increase the mean global temperature, possibly as much as 4.5 to 6°C [6,7]. In addition, shifts
in regional precipitation patterns as a result of rising atmospheric [CO 2 ] will probably result in decreased
soil water availability in many areas of the world [3,8–11].
Atmospheric CO 2 is an essential compound for life on earth. Through photosynthesis plants obtain
carbon for their growth and provide sustenance for other living things, ourselves included. In photosyn-
thesis, solar energy is absorbed by a system of pigments, and inorganic atmospheric CO 2 is fixed and re-
duced into organic compounds. Reduction of carbon is a major function of photosynthesis and is quanti-
fied by realizing that total plant organic matter is about 45% carbon on a dry weight basis. The
biochemistry of carbon reduction has attracted much research attention since the early 1950s, leading to
recognition of different biochemical pathways for net carbon flow during plant photosynthesis. Hu-
mankind, however, has not devised ways to manipulate or control this process because many foundations
of photosynthesis and knowledge of its regulatory mechanisms under environmental change are still not
fully understood [12,13]. Rising atmospheric [CO 2 ] could benefit many economically important crops,
especially the C 3 ; however, gains may or may not be realized in long-term growth because of the inter-
action of various environmental factors that complicate the issue [11,14].
This chapter focuses on the photosynthetic responses of crop plants to long-term elevated growth
[CO 2 ]. The physiological, biochemical, and molecular aspects of photosynthetic acclimation to rising at-
mospheric [CO 2 ] and interactive effects of elevated [CO 2 ] with anticipated simultaneous increases in air
temperature and/or decreases in soil water availability on leaf photosynthesis will be discussed. As the
photosynthetic mechanism of a plant species is the major determinant of how it will respond to rising at-