The Nitrogen Cycle

Created by Ted Park, Akshay Patel, and Sang Lee

What is nitrogen and why is it needed?● Nitrogen is a chemical element that is needed by living organisms● Nitrogen is a component of amino acids in proteins and bases in nucleic acids● Without nitrogen, organisms would not be able to grow or reproduce● Nitrogen (in the form of N2) makes up approximately 80 percent of the air in

the atmosphere● The triple bond in the nitrogen molecule (N2) makes the molecule inert

(unreactive) and stable

What is the nitrogen cycle and why is it important?● The nitrogen cycle is the transformation and movement of nitrogen between the

geosphere and biosphere● Although there is an abundance of nitrogen in the atmosphere, most plants cannot

use this form of nitrogen● Instead, nitrogen must be in its “fixed” form, or in a compound, for it to be usable by

plants● To get to this “fixed” form, nitrogen must first go through the cycle● The steps of the nitrogen cycle are the following:

○ Nitrogen Fixation○ Nitrification○ Denitrification○ Ammonification○ Assimilation○ Eutrophication

Nitrogen Fixation● Nitrogen fixation is the process in which nitrogen (N2 ) from the atmosphere is

converted to ammonia (NH3) and then to ammonium (NH4+)

● Ammonia is an organic form of nitrogen, so it can not be absorbed by plants● Ammonium is created when ammonia combines with a hydrogen ion (H+)● Natural or industrial processes (such as lightning and bacteria) cause free

nitrogen to combine with other elements to form these nitrogen compounds

Nitrification● Nitrification is the two-step process in which ammonia is converted to nitrites

(NO2-) and then to nitrates (NO3-).● Two different species of bacteria that are present in the soil oxidize the

ammonia into inorganic forms of nitrogen● The rate of nitrification is determined by these factors:

○ temperature dependency: rapid changes in temperature do not produce rapid changes in growth○ oxygen intake: nitrifying bacteria are sensitive to low oxygen concentrations ○ pH dependency: nitrification occurs the fastest when the pH is between 8 and 9○ prevention substances- many substances can prevent nitrification reactions such as metals

Assimilation● Assimilation is the is the process by which living organisms incorporate NO3-

and NH4+ ammonium formed through nitrogen fixation and nitrification● Plants take in this form of nitrogen via the roots and incorporate them into

nucleic acids and plant protein● Animals are then able to receive and utilize the nitrogen from plant tissues

through consumption

Ammonification● Ammonification occurs when a plant or animal dies or excretes waste● Decomposers, such as bacteria and fungi, first break down the proteins in the

organic matter ● This releases ammonia, which dissolves with the water in the soil ● Ammonia then combines with a hydrogen ion to create ammonium

Denitrification● Denitrification is the process in which microorganisms, such as bacteria, break

down nitrates to metabolize oxygen● This releases nitrogen gas back into the atmosphere, completing the cycle

Eutrophication● Eutrophication, which comes from the Greek word eutrophıa, meaning healthy,

adequate nutrition, development, is an ecosystem’s response to the addition of artificial/natural nutrients through detergents, fertilizers, or sewage

● Eutrophication occurs when nitrate leaches into a body of water

How do humans affect the nitrogen cycle?

- Humans affect the nitrogen cycle mainly in four different ways. Nitrogen fertilizer, deforestation, burning of fossil fuels, and the growth of human population.

Nitrogen Fertilizer- Each year, humans produce approximately 80 teragrams of nitrogen fertilizer.

For scale, one teragram is 2,204,622,621.85 lbs, 80 teragrams is 176,369,809,748 lbs,

- This immense amount of nitrogen enters the ecosystems of the planet and as of now, it is the largest contribution of new nitrogen into our planet by human race.

Deforestation- Forests and the plants within them have the ability to retain nitrogen.

Therefore when the trees are cut, the amount of nitrogen retained decreases and the amount being put out into the air increases.

Burning of Fossil Fuels- Transportation vehicles, power plants, industrial factories, and other man-made devices/buildings that rely on a combustion process to function increase the amount of nitrogen because the burning of fossil fuels sends back nitrogen that was trapped inside, thus causing an increase in the amount of nitrogen. This affects the nitrogen cycle.

Human Population Growth- Ultimately, with the growth of the human population comes come an increase in

demand. Therefore, more trees will be cut down, more factories will be made, more vehicles will be driven, and more fertilizer will be used.

- Therefore, there will evidently be an exponential increase in nitrogen as the population on Earth continues to grow.

Are they any solutions to this issue?● Reduce your usage of fossil fuels in your daily lives

○ Reduce, Reuse, and Recycle○ Carpool, walk, or bike to get around places○ Conserve power and electricity when possible

● In 2014, the United States consumed 6.97 billion barrels of petroleum alone● Another possible solution to this problem is to reduce the usage of nitrogen

fertilizer for agriculture ● This will then reduce eutrophication and damage in our ecosystems

Sources● http://www.visionlearning.com/en/library/Earth-Science/6/The-Nitrogen-

Cycle/98 ● http://www.nature.com/scitable/knowledge/library/the-nitrogen-cycle-

processes-players-and-human-15644632 ● http://archive.bio.ed.ac.uk/jdeacon/microbes/nitrogen.htm ● http://www.wisegeek.org/what-is-ammonification.htm ● http://www.fondriest.com/news/nitrogencycle.htm