Nitrogen cycle in nature

Numerical models of the global nitrogen cycle 4.4.2.1 Conceptual schemes of the nitrogen cycle in nature... 

By means of these changes much nitrogen from the animal or vegetable body is again thrown back into the atmosphere in its original form, thus maintaining the nitrogen cycle in nature. 

The addition of an arbitrary unit of nitrogen to the nitrogen cycle in nature is estimated to create an 800-fold flow in N cycling (93). It is no wonder that... 

Like CO2 and CH4, nitrous oxide has both natural and anthropogenic sources. The largest sources of N2O are associated with nitrogen cycling in natural and agricultural ecos)7stems (Section 2.4.2, Cycling of Carbon and Nutrients) nitrification and denitrification both release N2O (Haynes, 1986). N2O is abo formed as a b rproduct of fuel combustion. Human activities are estimated to have increased the release of N2O by 40-50% over... 

Fig. 12-2 Partitioning of the various forms of nitrogen in the atmosphere. Units are Tg N. (Reprinted with permission from R. Soderlund and T. Rosswall, The nitrogen cycles. In O. Huntizger (1982). "The Natural Environment and the Biogeochemical Cycles," p. 70, Springer-Verlag, Heidelberg.)...

Soderlund, R. and Svensson, B. H. (1976). The global nitrogen cycle. In "Nitrogen, Phosphorus and Sulfur - Global Cycles" (B. H. Svensson and R. Soderlund, eds), Ecol. Bull. No. 22, pp. 23-73, SCOPE. Swedish Natural Science Research Council, Stockholm. 

R.P. Hobson and H.J. Page, Studies on the carbon and nitrogen cycles in the soil, VIII, The nature of the organic nitrogen compounds of the soil non-humic nitrogen, J. Agr. Sci. 22 (1932)516-526. 

If we are satisfied to omit innumerable details, we can trace, for each of the most important chemical elements concerned, the broad outline of its cycle in nature. The elements and simple compounds principally concerned are carbon (COj), oxygen (O2), nitrogen (Nj, NH3, N02 , N03 ), water (H2O), phosphorous (P04 etc.). .. For the drama of life is like a puppet show in which stage, scenery, actors and all are made of the same stuff. The players, indeed, have their exits and their entrances, but the exit is by way of translation into the substance of the stage and each entrance is a transformation scene. So stage and players are bound together in the close partnership of an intimate comedy and if we would catch the spirit of the piece, our attention must not all be absorbed in the characters alone, but must be extended also to the scene, of which they... 

Williams, P.A., Fulop, V., Garman, E.F., Saunders, N.F.W., Ferguson, S.J., and Hajdu, J. (1997) Haem-ligand switching during catalysis in crystals of a nitrogen-cycle enzyme. Nature, 389, 406-412. 

In contrast, the nature of the surface nitrogen cycle in the Archaean is the subject of debate. Central to this discussion is when the nitrogen biogeochemical cycle began. For example, Mather et al. (2004) have suggested that in the Archaean nitrogen fixation was driven by nonbiological processes and that fixation rates were lower, probably of the order of 1011. However, their model depends upon some assumptions about the extent to which... 

As well as the sulfur cyde, there are other cycles in nature water, nitrogen, phosphorus and carbon. Man has influenced them all, but the sulfur cycle is the most disturbed among aU these cydic processes. Fossil fuels are burned in order to warm up houses and to provide cars, power stations and industries with energy. Then the sulfur that was built into coal, oil and natural gas, millions of years ago, is set free. It is transported as sulfur dioxide to the atmosphere, the SO content of which has increased considerably compared to the equilibrium content of the natural cyde. The acid gas is transported by the winds over the continents, and, long distances from a specific source, people experience a rain of sulfuric acid . This acid rain not only attacks the needles and leaves of trees but also damages the roots of plants. In acidified lakes the ability of fish to reproduce is disturbed. If acidification is not neutralized by liming, metal ions may be leached from rocks and damage animal life. 

As in the case of the nitrogen cycle, animals and plants are not indispensable to the operation of the sulphur cycle. In nature one sometimes encounters this cycle maintained by a microbiological association of autotrophic bacteria, algae and protozoa, the name sulphuretum is applied to this community which can be found in clays, muds and in stagnant waters. Figure 104 shows a bacterial sulphur cycle. 

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