C3-plants

Compartmentation of these reactions to prevent photorespiration involves the interaction of two cell types, mescrphyll cells and bundle sheath cells. The meso-phyll cells take up COg at the leaf surface, where Og is abundant, and use it to carboxylate phosphoenolpyruvate to yield OAA in a reaction catalyzed by PEP carboxylase (Figure 22.30). This four-carbon dicarboxylic acid is then either reduced to malate by an NADPH-specific malate dehydrogenase or transaminated to give aspartate in the mesophyll cells. The 4-C COg carrier (malate or aspartate) then is transported to the bundle sheath cells, where it is decarboxylated to yield COg and a 3-C product. The COg is then fixed into organic carbon by the Calvin cycle localized within the bundle sheath cells, and the 3-C product is returned to the mesophyll cells, where it is reconverted to PEP in preparation to accept another COg (Figure 22.30). Plants that use the C-4 pathway are termed C4 plants, in contrast to those plants with the conventional pathway of COg uptake (C3 plants). 

The major sources of variation in 8 C are the two C4 plants, maize and sugar cane. Most other foods are C3 and animals used for food were mainly feeding on C3 plants. Maize and sugar cane (in the form of molasses) are found... 

Where CO2 in the free atmosphere has a 5 C value of-7%o, C3 and C4 plants are anticipated to have 5 C values of about -26.5%o and -12.5%o respectively (van der Merwe 1989) archaeological maize, however, typically averages -9.5%o(Schwarcz et al. 1985). The isotopic values of modern maize and C3 plant foods in Mesoamerica (Wright 1994 203-206), after correction for the Industrial Effect, average -9.6%o and -26.4%o respectively. Since herbivore collagen is typically enriched by +5%o relative to the diet (van der Merwe 1989), animals from this region with a pure C3 plant diet should... 

Table 2.2. Carbon isolope values in collagen of modern and ancicni fauna wiih C3 plant diets. The isotope values for ancient armadillo were not included in the average since they dearly consumed some C4 plants.

BIOGENIC ISOTOPIC SIGNALS USED TO ASSESS THE PRESERVATION OF ISOTOPIC SIGNALS IN FOSSIL SAMPLES FROM C3 PLANT FOOD WEBS... 

Figure 4.1. 8 C values of bone collagen in C3 plant ecosystems.

In making the reasonable assumption that browser diets should have remained consistent through time, it was also assumed that C7 C ratios of their C3 foliage diets would not have changed. This is not the case environmental parameters such as aridity, osmotic stress, temperature, pCOi and irra-diance have predictable effects on ratios of C3 plants (summarized in... 

Tieszen 1991). Water stress, for instance, lowers photo synthetic discrimination against C, resulting in isotopic enrichment. C4 plants are not affected isotopically by environmental parameters although their distributions are (Ehleringer et al. 1997). Under conditions of increasing aridity, the climate variable of most likely importance in African sites, C3 plants should become slightly more enriched on average. Therefore one should be cautious about use... 

Figure 10.4. Effect on apatite-collagen isotopic fractionation due to inhibition of amino acid production and preferred use of exogenous amino acids. Carnivore and herbivore, both based on C3 plants, have similar bulk isotopic composition of total edible tissues (T), leading to similar 5 C for apatite carbonate (AP). Collagen (CO) of carnivore is more enriched in Cthan that of herbivore, because of preferential utilization of amino acids derived from protein (P) of herbivore flesh in construction of carnivore s proteins. C ss = assimilated carbon.

P. Hogberg and A. Ekblad, Substrate-induced respiration measured in situ in a C3-plant ecosystem using additions of C4-sucrose. Soil Biol. Biochem. 2 1131 (1996). 

More than 95% of the plants of the world follow the C3path, whereby the carbon dioxide is initially incorporated, by the plants, into intermediate compounds made up of three atoms of carbon - which is the reason these plants are known as C3 plants. Only about 1% of all plants, including maize, millet, sorghum, and sugarcane, follow the C4 path, incorporating carbon dioxide into intermediate compounds made up of four atoms of carbon - which is the reason these plants are known as C4 plants. The remaining 4% of plants, mostly succulents (cacti), follow the third, CAM, path, which has no bearing on the discussion that follows. 

C3 plants Plants as, for example, cotton and wheat, in which, during the photosynthesis process, a stable compound consisting of three bonded carbon atoms is first formed during the fixation of carbon derived from carbon dioxide in the plants over 95% of the plant species on the earth are C3 plants see C4 and CAM plants. 

Ineson P, Cotmfo MF, Bol R, Harkness DD, Blum H (1996) Quantification of soil carbon inputs under elevated C02 C3 plants in a C4 soil. Plant Soil 187 345-350... 

An important benefit of the isotopic approach is that below-ground biomass values are not required. The 13C natural abundance isotopic carbon budget approach is based on C3 plants having lower 13C value than C4 plants (Ehleringer 1991 Clay et al. 2006) and that the signatures can be tracked by placing C3 plant residue into a soil derived from C4 plants or vice versa. In these calculations, several definitions are needed. These definitions include... 

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