Carbon fixation

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Carbon fixation is a process found in autotrophs, usually driven by photosynthesis, whereby carbon dioxide is converted into organic compounds. In plants, there are three types:

• C₃ - plant that uses the Calvin Cycle for the initial steps that incorporate CO₂ into organic matter, forming a 3-carbon compound as the 1^st stable intermediate. Most broadleaf plants and plants in the temperate zones are C3.

• C₄ - plant that prefaces the Calvin Cycle with reactions that incorporate CO₂ into 4-carbon compound. C4 plants have a distinctive leaf anatomy. This pathway is found mostly in hot regions with intense sunlight. Tropical grasses, such as sugar cane and maize are C4 plants, but there are many broadleaf plants that are C4.

• CAM - plant that uses Crassulacean acid metabolism as an adaptation for arid conditions. CO₂ entering the stomata during the night is converted into organic acids, which release CO₂ for the Calvin Cycle during the day, when the stomate is closed. The jade plant (Crassula ovata) and Cactus species are typical of CAM plants.

[edit] Genetics

C3 and C4 plants may be present within a single taxonomic group, for example species of Atriplex (saltbush). Experimental crosses between C3 and C4 Atriplex species have demonstrated that many genes are involved in the differences between C3 and C4 plants.