Yield and Growth of Plants With Increased CO2 Levels

Why CO2 is Important to Plants

• Plants use a process called photosynthesis to convert the radiant energy of the sun into useable chemical energy. Spurred by solar energy, they absorb water and carbon dioxide and convert them into sugars, which are then synthesized into adenosine triphosphate via cellular respiration. Photosynthesis also releases oxygen, which has the net result of removing carbon dioxide from the atmosphere, replacing it with breathable oxygen. Carbon dioxide is thus an essential chemical component in the reactions fueling photosynthesis.

Increases in Atmospheric CO2

• Increases in CO2 typically result in higher yields and increased growth and reproduction, provided other growth factors like sunlight, temperature and precipitation remain constant. Carbon dioxide is usually the limiting factor in photosynthesis reactions, and its increase has the potential to increase plant yields from 22 to 41 percent, according to a 1993 study by H. Poorter, published in the journal "Vegetation." In short, increased levels of atmospheric CO2 result in increased plant growth.

Negative Effects of Increased CO2

• New studies suggest that elevated CO2 levels accompanying global climate change might actually restrict plant growth, rather than stimulating it. CO2 leads to more vigorous plant growth, provided it is the only element increased beyond normal levels, but environmental factors accompanying increased levels of carbon dioxide in the atmosphere can negate this effect. A 2002 study conducted by Stanford University found that higher temperatures and nitrogen levels, along with increased precipitation, negated the increased growth spurred by higher CO2 levels. When temperature, water and nitrogen are kept at normal levels, the addition of CO2 leads to more plant growth; when they are increased, CO2 actually retards plant growth.

Agricultural Implications

• Although rising levels of atmospheric carbon dioxide have the potential to increase agricultural yields under the right conditions, this increased growth comes at the price of lower nutritional value. Researchers at Ohio State University recently found that plants subjected to increased CO2 levels produced more flowers, seeds and fruit than those grown under normal conditions, but the resulting produce had much lower nitrogen levels. Nitrogen is an essential element in both human and animal protein synthesis, and widespread decreases in crops could have significant implications for global food security.