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ARS Home » Research » Publications at this Location » Publication #129018
Title: CARBON DIOXIDE, PLANTS, AND TRANSPIRATION

Author
item Allen Jr, Leon
item Vu, Joseph
item SHEEHY, J - INTNL RICE RSCH INSTITUTE

Submitted to: Encyclopedia of Water Science
Publication Type: Book / Chapter
Publication Acceptance Date: 9/19/2002
Publication Date: 7/22/2003
Citation: Allen Jr, L.H., Vu, J.C. 2003. Carbon dioxide, plants, and transpiration. In: Stewart, B.A., Howell, T., editors. Encyclopedia of Water Science. New York: Marcel Dekker. p. 57-61

Interpretive Summary: Rising atmospheric carbon dioxide (CO2) is expected to cause global warming, but rising CO2 will also affect photosynthesis, growth, and transpiration of plants directly. ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL have analyzed these effects. For a doubling of CO2, photosynthesis will be increased about 50 percent and seed yields will be increased about 30 percent. Although a doubling of CO2 will decrease leaf transpiration about 40 percent, whole crop transpiration will be decreased only about 10 percent. Energy balance analysis of the crop explains this apparent paradox. On the other hand, expected global warming could increase transpiration by 8 to 35 percent, and thus offset the water-savings effect of CO2, based on estimated global warming between 1.4 to 5.8 degrees Celsius. Likewise, crop seed yields could be decreased by 14 to 58 percent, depending on the severity of warming. Our analysis shows that increasing CO2 will increase yields and decrease water use by crops, but anticipated global warming could offset these benefits.

Technical Abstract: Carbon dioxide (CO2) increased from 280 ppm in pre-industrial times to 315 ppm in 1958, and on to 370 ppm today. This increase is expected to cause global warming, but rising CO2 will also affect plant photosynthesis, growth, and transpiration directly. For a doubling of CO2, photosynthetic rate increases for C3 plants will be about 50 percent, but seed yield increases will be about 30 percent. Although a doubling of CO2 will decrease stomatal conductance about 40 percent, whole crop transpiration will be decreased only about 10 percent. This paradox can be explained by energy balance analysis of the crop. However, expected global warming could increase crop transpiration by 8 to 35 percent, and thus offset the water-savings of doubled CO2, based on IPCC estimates of a global warming by 1.4 to 5.8 Celsius. Likewise, seed yields could be decreased by 14 to 58 percent, depending on the severity of global warming. Thus, increasing CO2 will increase yields and decrease water use by crops, but anticipated warming could more than offset these benefits.