In hot, sunny climes, these C4 plants are half as efficient again as their C3 counterparts.
Other researchers, meanwhile, are trying to isolate the genes responsible for C4 plants' unusual anatomy and biochemistry.
In fact, the distinction between C3 and C4 plants is not always clear-cut.
C4 plants often absorb CO2 from the air in one type of cell and then convert it to sugars through photosynthesis in another.
Although C4 plants evolved to cope with low levels of carbon dioxide, the workaround comes at a price, since it takes additional chemical energy.
WSJ: Harrison H. Schmitt and William Happer: In Defense of Carbon Dioxide
Success would not only increase yields, but also reduce the need for water and fertilisers, since C4 plants make more efficient use of both.
Called C4 plants because they utilize a molecule with four carbons, plants that use this evolutionary trick include sugar cane, corn and other tropical plants.
WSJ: Harrison H. Schmitt and William Happer: In Defense of Carbon Dioxide
Some C4 plants, for example, absorb CO2 and photosynthesise it at either end of special elongated cells, instead of separating the functions out into two different types of cell.
With high levels of carbon dioxide in the atmosphere, C4 plants are not as productive as C3 plants, which do not have the overhead costs of the carbon-dioxide enrichment system.
WSJ: Harrison H. Schmitt and William Happer: In Defense of Carbon Dioxide
Whether plants are C3 or C4, the way they get carbon dioxide from the air is the same: The plant leaves have little holes, or stomata, through which carbon dioxide molecules can diffuse into the moist interior for use in the plant's photosynthetic cycles.
WSJ: Harrison H. Schmitt and William Happer: In Defense of Carbon Dioxide
Many C3 plants, meanwhile, have several of the genes needed for C4 photosynthesis, but do not use them in the same way.
As a result, certain plants in warm climates have evolved a different mechanism, called C4 photosynthesis, in which other enzymes help to concentrate CO2 around the rubisco, and the initial result is a four-carbon sugar.
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