Ecological trends

One interesting story involving carbon isotopes in bioapatites concerns the different photosynthetic pathways used by terrestrial plants (Fig. 2) and the animals that eat them. Carbon-isotope discrimination among plants has been described well in a pair of comprehensive reviews by O Leary (1988) and Farquhar et al. (1989). The main controls on fractionation are the action of a particular enzyme and the leakiness of cells. 

Atmospheric CO2 first moves through the stomata, dissolves into leaf water, and so enters the mesophyll cell. Most dicotyledonous plants (dicots) as well as monocotyl-edenous plants (monocots) in regions with cool growing seasons use the C3-photosynthetic pathway. Mesophyll CO2 is directly combined with ribulose bisphosphate (RuBP—a 5-carbon molecule), in a reaction catalyzed by the enzyme ribulose bisphos- 

Many monocots use the C4 photosynthetic pathway. CO2 in mesophyll cells is first combined with phosphoenolpyruvate (PEP) via the enzyme PEP carboxylase (PEPc) to make the molecule oxaloacetate (OAA), which has 4 carbon atoms (hence C4 ). The OAA is usually transformed into malate, which is transported into bundle sheath cells and cleaved to pyruvate and CO2 again. The pyruvate is recycled back into the mesophyll cells to reform PEP. Unlike mesophyll cells, the bundle sheath cells in C4 plants are able to concentrate CO2 (i.e., they are not very leaky), so that most of the CO2 is fixed, and less fractionation occurs in forming PGA. If bundle sheath cells were perfectly gas tight, there would be zero fractionation from Rubisco, whereas if the cells were completely permeable to CO2, the isotope fractionation from Rubisco would be —25%o. In reality, bundle sheath cells can exhibit some leakiness, so there can be some Rubisco discrimination, but far less than in mesophyl cells. 

Other photo synthetic steps also have isotope fractionations, particularly diffusion of CO2 across stomata ( 4%o). However, the isotopic difference between C3 vs. C4 plants is largely influenced by the degree to which the Rubisco isotope discrimination is dominant, which depends on the degree to which cells are C02-leaky. Because mesophyll cells are very leaky but bundle sheath cells are not, C3 vs. C4 plants have depletions of 18%o vs. 4%o relative to atmospheric CO2. Therefore, in the modern world (5 C of atmospheric CO2 is -8%o), most C3 dicots have values from about -25 to -30%o 

Other factors can influence the of plant tissues and hence bioapatite. CO2 in 

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Daims H, Taylor MW, Wagner M (2006) Wastewater treatment a model system for microbial ecology. Trends Biotechnol 24 483 189... 

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Properties, processability and prices are intermediate between those of ABS and PVC. Like PVC, these alloys are handicapped by their halogen content, which conflicts with ecological trends. 

Ettema, C. H. Wardle, D. A. (2002). Spatial soil ecology. Trends in Ecology and Evolution 17, 177-83. 

New developments in the different types of chemical finishing have been described in the relevant chapters and new kinds of finishing are the subject of the chapter on novel finishes. In this chapter tendencies in the development of chemical finishing, including technical, economical and ecological trends, will be pointed out. On this basis, and as far as it is possible to predict, an extrapolation to the future will be attempted. Table 19.1 gives an overview of these trends. 

Inderjit et al. (2006) Can plant biochemistry contribute to understanding of invasion ecology. Trends Plant Sci. 11, 574-580... 

External influences, such as national legislation, can also be immensely significant Ecological trends play a strong role, particularly in areas like solvent waste management, which strengthens the case for the development of solvent-free material systems and technologies. 

The lEP provides the monitoring fi amework to characterize the status and trends of Delta aquatic ecosystems. The lEP strives to provide information on the many factors that affect ecological resorrrces in the Delta. Key near-term goals for the lEP include (1) collecting and analyzing data needed to understand factors controlling the distribution and abundance of selected fish and wildlife resources, (2)... 

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But this trend can and must be changed. Agriculture is one of the many industries and activities that have degraded the environment, and modern science has alerted us to the fact that ecology is destiny (Freedgood, 1997). 

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Springael D, Top EM (2004) Horizontal gene transfer and microbial adaptation to xenobio-tics new types of mobile genetic elements and lessons from ecological studies. Trends Microbiol 12 53-58... 

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