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C3 and C4 Plants
Almost all plant life on Earth can be broken into two categories based on the way they assimilate carbon dioxide into their systems.
C3 plants include more than 95 percent of the plant species on earth. (Trees, for example, are C3 plants.)
C4 plants include such crop plants as sugar cane and corn. They are the second most prevalent photosynthetic type.
During the first steps in CO2 assimilation, C3 plants form a pair of three carbon-atom molecules. C4 plants, on the other hand, initially form four carbon-atom molecules.
It turns out that the important difference between C3 and C4 species for rising CO2 levels is that C3 species continue to increase photosynthesis with rising CO2 , while C4 species do not. So, C3 plants that can respond readily to higher CO2 levels, and C4 plants can make only limited responses.
Thus increased CO2 likely will mean that some plant species will be stronger, more prolific, and may overwhelm those less able to benefit. The nature of plant populations in various areas probably will change; more sedges in place of grasses in marshlands, for example, consequences we don't yet know.
At our research sites, we are looking at how these different classes of plants respond to increased CO2 levels, and the broader implications for the ecosystems in which they live. http://www.serc.si.edu/labs/co2/c3_c4_plants.jsp