Ver el código de «Ehleringer, J. R., Monson, R. K. 1993.»

'''Ehleringer, J. R., Monson, R. K. 1993.''' Evolutionary and ecological aspects of photosynthetic pathway variation. Annual review of ecology and systematics '''24''':411-439
==Abstract==
C<sub>4</sub>{{ref|C4}} and CAM{{ref|CAM}} photosynthesis are evolutionarily derived from C<sub>3</sub>{{ref|C3}} photosynthesis. The morphological and biochemical modifications necessary to achieve either C<sub>4</sub> or CAM photosynthesis are thought to have independently arisen numerous times within different higher plant taxa. It is thought that C<sub>4</sub> photosynthesis evolved in response to the low atmospheric CO<sub>2</sub> concentrations that arose sometime after the end of the Cretaceous. Low CO<sub>2</sub> concentrations result in significant increases in photorespiration of C<sub>3</sub> plants, reducing productivity; both C<sub>3</sub>-C<sub>4</sub> intermediate and C<sub>4</sub> plants exhibit reduced photorespiration rates. In contrast, it may be argued that CAM arose either in response to selection of increased water-use efficiency or for increased carbon gain. Globally, all three pathways are widely distributed today, with a tendency toward ecological adaptation of C<sub>4</sub> plants into warm, monsoonal climates and CAM plants into water-limited habitats. In an anthropogenically altered CO<sub>2</sub> environment, C<sub>4</sub> plants may lose their competitive advantage over C<sub>3</sub> plants.
<small>

==Apostillas==
#{{notas|C4}}. C<sub>4</sub> carbon fixation is one of three biochemical processes, along with C<sub>3</sub> and CAM photosynthesis, that fixes carbon. It is named for the 4-carbon molecule of the first product of carbon fixation found in the small subset of plants that use the C<sub>4</sub> process. This process is in contrast to the 3-carbon molecule products of C<sub>3</sub> plants. C<sub>4</sub> fixation is an elaboration of the more common C<sub>3</sub> carbon fixation and is believed to have evolved more recently. C<sub>4</sub> and CAM overcome the tendency of the enzyme RuBisCO to wastefully fix oxygen rather than carbon dioxide in the process of '''photorespiration'''. This is achieved in a more efficient environment for RubisCo by shuttling CO<sub>2</sub> via malate or aspartate from mesophyll cells to bundle-sheath cells. In these bundle-sheath cells, RuBisCO is isolated from atmospheric oxygen and saturated with the CO<sub>2</sub> released by decarboxylation of the malate. C<sub>4</sub> plants use PEP carboxylase to capture more CO<sub>2</sub> in the mesophyll cells. PEP Carboxylase (3 carbons) binds to CO<sub>2</sub> to make oxaloacetic acid (OAA). The OAA then makes malate (4 carbons). Malate enters bundle sheath cells and releases the CO<sub>2</sub> where RuBisCO works more efficiently. These additional steps, however, require more energy in the form of ATP. Because of this extra energy requirement, C<sub>4</sub> plants are able to more efficiently fix carbon in drought, high temperatures, and limitations of nitrogen or CO<sub>2</sub>, while the more common C<sub>3</sub> pathway is more efficient in the other conditions. [https://en.wikipedia.org/wiki/C4_carbon_fixation C4_carbon_fixation:wikipedia]
#{{notas|CAM}}. ''Crassulacean acid metabolism'', also known as ''CAM photosynthesis'', is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO<sub>2</sub>). The CO<sub>2</sub> is stored as the four-carbon acid malate in vacuoles at night, and then in the daytime, the malate is transported to chloroplasts where it is converted back to CO<sub>2</sub>, which is then used during photosynthesis. The pre-collected CO<sub>2</sub> is concentrated around the enzyme RuBisCO{{ref|rubisco}}, increasing photosynthetic efficiency. This metabolism was first studied in plants of the ''Crassulaceae'' family. These mainly include succulents. The first time it was studied, '''Crassula''' was used as a model organism. [https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism CAM:wikipedia]
#{{notas|C3}}. C<sub>3</sub> carbon fixation is one of three metabolic pathways for carbon fixation in photosynthesis, along with C<sub>4</sub> and CAM. This process converts carbon dioxide and ribulose bisphosphate (RuBP, a 5-carbon sugar) into 3-phosphoglycerate through the following reaction: '''CO<sub>2</sub> + H<sub>2</sub>O + RuBP → (2) 3-phosphoglycerate'''. Plants that survive solely on C<sub>3</sub> fixation (C<sub>3</sub> plants) tend to thrive in areas where sunlight intensity is moderate, temperatures are moderate, carbon dioxide concentrations are around 200 ppm or higher,[1] and groundwater is plentiful. The C<sub>3</sub> plants, originating during Mesozoic and Paleozoic eras, predate the C<sub>4</sub> plants and still represent approximately 95% of Earth's plant biomass. C<sub>3</sub> plants lose 97% of the water taken up through their roots to transpiration. Examples include rice and barley. C<sub>3</sub> plants cannot grow in very hot areas because RuBisCO incorporates more oxygen into RuBP as temperatures increase. [https://en.wikipedia.org/wiki/C3_carbon_fixation C3 carbon fixation: wikipedia]
#{{notas|rubisco}}. Ribulose-1,5-bisphosphate carboxylase/oxygenase, commonly known by the abbreviations RuBisCO or RuBPCase, is an enzyme involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants and other photosynthetic organisms to energy-rich molecules such as glucose. In chemical terms, it catalyzes the carboxylation of ribulose-1,5-bisphosphate (also known as RuBP). It is probably the most abundant enzyme on Earth. [https://en.wikipedia.org/wiki/RuBisCO RuBisCO]
</small>

[[categoría:bibliografía]]