Author
 |
Vu, Joseph |
|
Submitted to: Book Chapter
Publication Type: Other Publication Acceptance Date: 8/12/2004 Publication Date: 7/5/2005 Citation: Vu, J.C.V. 2005 Rising atmospheric CO2 and C4 photosynthesis: Handbook of Photogynthesis 2nd Edition (M. Lessarakli, ed.) CRC Press Taylor & Francis group, Boca Raton, Florida pp. 315-326 Interpretive Summary: A doubling of the global atmospheric carbon dioxide level (CO2), currently at about 370 parts per million, is expected within this century. Present atmospheric CO2 limits performance of many agricultural crop plants, which therefore sense and respond to rising CO2 through photosynthesis, a process by which leaves absorb CO2 from the air to make compounds required for plant growth. Exposure of plants belonging to the C3 photosynthetic group, which includes typical crop plants such as soybean and rice that produce a three-carbon acid as the first stable photosynthetic intermediate, to elevated CO2 generally results in stimulated photosynthesis and enhanced growth. However, exposure of plants belonging to the C4 photosynthetic group, which includes typical crop plants such as maize, sorghum and sugarcane that produce a four-carbon acid as the first stable photosynthetic intermediate, to elevated CO2 stimulates growth with little or no enhancement in photosynthesis. USDA, ARS, Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Florida are investigating how the C4 photosynthesis mechanism responds to rising CO2 and other global climate change parameters. Understanding the causes leading to an enhancement in C4 biomass at elevated CO2 could potentially be transmitted into a basic framework for improvement of C4 crop plants in a future rising atmospheric CO2 and climate-changed world. Technical Abstract: This review examines current knowledge on leaf photosynthesis of C4 crop plants in response to elevated atmospheric CO2. Research on rising atmospheric CO2 has focused mainly on C3 plant species. The capability of C4 plants to concentrate CO2 in the bundle sheath cells to levels up to 3 to 20 times higher than atmospheric CO2 has led to the widespread anticipation of little or no growth response to elevated CO2 levels. Nevertheless, the literature does reveal a positive growth response of many C4 crop plants to elevated atmospheric CO2, although to a smaller extent than that of C3 plants. Such increases in biomass are not easily explained, because C4 plants often show little or no enhancement in leaf photosynthetic rates, which is in contrast to the C3 species. Elevated CO2 may affect C4 plants, only at certain stages of leaf/plant growth and development, and via several mechanisms including reduction in stomatal aperture and conductance, improvement in water-use efficiency, increase in leaf temperature and enhancement in tillering and leaf area. As the impact of C4 agricultural crops such as maize, sorghum, millet and sugarcane on world food supply is enormous, there is a need to unravel the causes/ mechanisms leading to the enhancement in C4 biomass under elevated atmospheric CO2. |
