Nitrogen fixation cycle

A low oxidation state of the metal would also tend to produce a coordination site at which ammonia would bind weakly and be displaced by the more strongly binding dinitrogen, thus facilitating the next stage of a nitrogen-fixation cycle. This substitution has indeed been observed on the [Mo(N2)(dppe)2] site (95). 

Fig. 10-13. The links between the cycling of C, N, and O2 are indicated. Total primary production is composed of two parts. The production driven by new nutrient input to the euphotic zone is called new production (Dugdale and Goering, 1967). New production is mainly in the form of the upward flux of nitrate from below but river and atmospheric input and nitrogen fixation (Karl et al, 1997) are other possible sources. Other forms of nitrogen such as nitrite, ammonia, and urea may also be important under certain situations. The "new" nitrate is used to produce plankton protoplasm and oxygen according to the RKR equation. Some of the plant material produced is respired in the euphotic zone due to the combined efforts...

Gruber, N. and Sarmiento, J. L. (1997). Global patterns of marine nitrogen fixation and denitrification. Glob. Biogeochem. Cycles 11,235-266. 

Karl, D., Letelier, R., Tupas, L. et al. (1997). The role of nitrogen fixation in biogeochemical cycling in the subtropical North Pacific Ocean. Nature 388, 533-538. 

Galloway J. N. et al. (1995). Nitrogen fixation Anthropogenic enhancement - environmental response. Global Biogeochem. Cycles 9,235-252. 

Granhall, U. (1981). Biological nitrogen fixation in relation to environmental factors and functioning of natural ecosystems. In "Terrestrial Nitrogen Cycles" (F. E. Clark and T. Rosswall, eds). Ecological Bulletin 33, 131-145. Swedish Natural Science Research Council, Stockholm. 

The biogeochemical cycling of nitrogen is very much controlled by redox reactions. This perspective is presented in Figure 24.3 for the redox reactions that take place in the water column and sediments. The major pathways of reduction are nitrogen fixation, assimilatory nitrogen reduction, and denitrification. The major oxidation processes are nitrification and anaerobic ammonium oxidation (anammox). Each of these is described next in further detail. 

Table 24.3 Estimates of the Total Annual Contribution of Combined Nitrogen to the Global Nitrogen Cycle by Nitrogen Fixation in Benthic Marine Environments. ...

The process of nitrogen fixation is an essential part of the nitrogen cycle on the planet earth(l). It is estimated that greater than 60Z of the N2 that is ultimately converted to NH4+ is done so by the nitrogenase enzyme system. The availability of fixed nitrogen is often the limiting factor in plant growth( ). To... 

Bacterial ferredoxins function primarily as electron carriers in ferredoxin-mediated oxidation reduction reactions. Some examples are reduction of NAD, NADP, FMN, FAD, sulfite and protons in anaerobic bacteria, CO -fixation cycles in photosynthetic bacteria, nitrogen fixation in anaerobic nitrogen fixing bacteria, and reductive carboxylation of substrates in fermentative bacteria. The roles of bacterial ferredoxins in these reactions have been summarized by Orme-Johnson (2), Buchanan and Arnon (3), and Mortenson and Nakos (31). 

Terms in bold are defined in the nitrogen cycle 834 nitrogen fixation 834 symbionts 834 nitrogenase complex 835 leghemoglobin 836 glutamine synthetase 838 glutamate synthase 838 glutamine amidotransferases 840 5-phosphoribosyl-l-... 

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