Nitrogen Cycle as the Most

¶ … Nitrogen Cycle

As the most abundant element in the Earth's atmosphere, nitrogen might be thought to be an easily accessible nutrient for the planet's many life forms. In fact, however, nitrogen's abundance has very little to do with its availability as a nutrient in any sort of direct way. Before the nitrogen gas -- N2 -- in the atmosphere can be utilized by plants -- and before those plants can be eaten by organisms higher on the food chain like human beings -- it has to be converted into different forms (Kimball 2008). Namely, it has to be taken out of its gaseous state and converted to other forms in other molecules in order to be absorbed and used by plants (Harrison 2003). The process by which this occurs is one of the most remarkable and one of the most necessary cycles to have come into existence, and is both fairly simple and, on a deeper and more practical level, stil not fully understood.

The first step in the nitrogen cycle is nitrogen fixation. In this process, bacteria and some other microorganisms in the Earth's soil convert atmospheric nitrogen gas into ammonia, managing to split each double-atom molecule of nitrogen gas and pairing each individual atom with three hydrogen atoms (Harrison 2003). The manner in which bacteria manage this feat -- both the splitting of the nitrogen gas molecule and the fusion of the ammonia molecule -- is not fully understood by science; industrialization has allowed for the human creation of ammonia from the raw elements, but it requires great heat and pressure -- far more energy than the bacteria and microorganisms exert doing the same job (Kimball 2008). Regardless, this process does take place, and the ammonia is either used directly by plants or is further converted by bacteria before being taken up by other organisms.

At this point, the nitrogen has become fixed and is now usable by all organisms on the food chain. When organisms higher on the food chain -- like human beings -- eat plants and other organisms lower on the food chain, they absorb and utilize the nitrogen that was originally fixed by these bacteria (Harrison 2003). In this way, the nitrogen from the atmosphere is able to make it through the entire biosphere. The cycle is not complete, however, until the nitrogen is returned back to the atmosphere. This occurs when higher organisms die, and decay (as well as metabolic process of other bacteria and fungi) converts the fixed nitrogen back to ammonia, or even further into nitrates which will eventually break down further and become nitrogen gas again, returning to the atmosphere (Kimball 2008). Sometimes the nitrogen products of decay return to the soil or directly to plants, and other byproducts can actually build up to toxic levels in soil and in the world's oceans (Harrison 2003). In this latter regard, much if the blame lies with the artificial manipulation of the nitrogen cycle through human industrial activities and fertilization.