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"What is the significance of the nitrogen cycle in ecosystems? Using suitable examples, discuss the role of microorganisms in the Nitrogen Cycle. How can Man influence the Nitrogen Cycle?"

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Introduction

"What is the significance of the nitrogen cycle in ecosystems? Using suitable examples, discuss the role of microorganisms in the Nitrogen Cycle. How can Man influence the Nitrogen Cycle?" Nitrogen makes up about 80 per cent of the Earth's atmosphere as a gas. However the gaseous molecule is very stable and has to be transformed before it can be used by most organisms as it is only available to them when it is ammonium or nitrate. It can only be removed from the atmosphere in two ways: by lightning and by nitrogen fixation. Only a few species can convert nitrogen by nitrogen fixation to biologically useful forms. Due to this, biologically useful nitrogen is often in short supply and can be the limiting factor in an ecosystem. There are five main steps in the Nitrogen cycle: Biological Nitrogen Fixation This is the conversion of gaseous nitrogen to ammonia using an enzyme called nitrogenase that only works in the absence of oxygen and requires large amounts of energy. ...read more.

Middle

The other method of nitrogen fixation is through lightning. The enormous energy of lightning breaks nitrogen molecules and enables their atoms to combine with oxygen in the air to form nitrogen oxides. These dissolve in rain, forming nitrates, that are carried to earth. Nitrification Nitrification is the conversion of ammonia to nitrate by soil bacteria. It is a two stage process. In the first stage Nitrosomonas utilise ammonia (NH ) as an energy source to oxidise it to nitrites ( NO ). In the second stage Nitrobacter oxidise the nitrites to nitrates (NO ). Both of these stages require oxygen and so must be performed in the presence of free oxygen. These two groups of autotrophic bacteria are called nitrifying bacteria. Plants take up the NO released by the bacteria and convert it to organic molecules such as amino acids. Assimilation This is the uptake of nitrite or ammonia by primary producers and its incorporation into proteins or nucleic acids. ...read more.

Conclusion

When a farmer plants a non-leguminous plant continuously on the same soil the nitrogen availability decreases. A way this is solved is by planting leguminous plants which enrich the soil by the root nodule bacteria releasing nitrogen. This can also benefit plants nearby as it increases the amount of nitrogen available in the area. Crop rotation involving periods of growing leguminous plants can be used to help improve the soil. This means farmers don't always need to use expensive and environmentally damaging synthetic nitrogen fertilisers. When used, often the nutrients from the fertilisers can be leached from the soil especially when they have been applied at the wrong time of year, just before heavy rain or in excessive quantities. This means the plants are unable to use the nutrients before they are leached from the soil. The excess fertiliser is carried away to adjacent water bodies where toxic cyanobacteria can increase due to the increase in nutrient levels. This can also lead to deoygenation of the water column due to the increased respiration or decomposition. This nutrient enrichment of natural water bodies as a result of pollution is called eutrophication. ...read more.

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