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C3 and C4 plants(1) stomata stay open all day and close at night. CAM plants(2) stomata open during the morning and close slightly at noon and then open again in the evening.
C 3 carbon fixation occurs in all plants as the first step of the Calvin–Benson cycle. (In C 4 and CAM plants, carbon dioxide is drawn out of malate and into this reaction rather than directly from the air.) Cross section of a C 3 plant, specifically of an Arabidopsis thaliana leaf. Vascular bundles shown.
English: C3 and C4 plants(1) stomata stay open all day and close at night. CAM plants(2) stomata open during the morning and close slightly at noon and then open again in the morning. CAM plants(2) stomata open during the morning and close slightly at noon and then open again in the morning.
Other plants show "inducible CAM", in which they are able to switch between using either the C 3 or C 4 mechanism and CAM depending on environmental conditions. Another group of plants employ "CAM-cycling", in which their stomata do not open at night; the plants instead recycle CO 2 produced by respiration as well as storing some CO 2 during ...
The δ 13 C of C3 plants depends on the relationship between stomatal conductance and photosynthetic rate, which is a good proxy of water use efficiency in the leaf. [19] C3 plants with high water-use efficiency tend to be less fractionated in 13 C (i.e., δ 13 C is relatively less negative) compared to C3 plants with low water-use efficiency. [19]
During the day, CAM plants close stomata and use stored acids as carbon sources for sugar, etc. production. The C3 pathway requires 18 ATP and 12 NADPH for the synthesis of one molecule of glucose (3 ATP + 2 NADPH per CO 2 fixed) while the C4 pathway requires 30 ATP and 12 NADPH (C3 + 2 ATP per CO 2 fixed).
Stomatal conductance, usually measured in mmol m −2 s −1 by a porometer, estimates the rate of gas exchange (i.e., carbon dioxide uptake) and transpiration (i.e., water loss as water vapor) through the leaf stomata as determined by the degree of stomatal aperture (and therefore the physical resistances to the movement of gases between the air and the interior of the leaf).
This ability to avoid photorespiration makes these plants more hardy than other plants in dry and hot environments, wherein stomata are closed and internal carbon dioxide levels are low. Under these conditions, photorespiration does occur in C 4 plants, but at a much lower level compared with C 3 plants in the same conditions.