Toby Sandblom, Andrew Ward, and Rachel Clarkson

Nitrogen Cycle

About Nitrogen

● Necessary for all living things

● Essential component for DNA, RNA, and proteins (the building blocks of life)

● Takes up 78% of the atmosphere as N2

● Major component of chlorophyll and is essential for photosynthesis

● The Nitrogen Cycle is a process by which nitrogen is converted between its various forms.

● Key Processes:o Nitrogen Fixationo Nitrificationo Assimilation o Ammonificationo Denitrification

● Affects rate of primary production and decomposition● Nitrogen transformation is controlled by microorganisms, particularly

bacteria● Occurs within atmosphere, lithosphere, hydrosphere, and biosphere

The Nitrogen Cycle

Diagram

Nitrogen Fixation● Occurs in Lithosphere● Conversion of gaseous nitrogen to ammonia NH3

● Combustion, lightning discharges, industrial processes etc.-> supply enough energy to break apart atmospheric nitrogen (fix considerable nitrogen)

● Nitrogen-fixing bacteria (ex: cyanobacteria) carry out biological nitrogen fixation in soil & aquatic environmentso makes use of enzyme nitrogenase to split atmospheric

nitrogen & combine resulting nitrogen atoms with hydrogen

● Symbiotic Nitrogen Fixationo Many microorganisms fix nitrogen

symbiotically by partnering with a host plant.● Nitrogen Fixation by Heterotrophs

o bacteria live in the soil and fix significant levels of nitrogen without the direct interaction with other organisms.

Nitrogen Fixation (continued)

● The conversion of ammonia or ammonium to nitrate

● Performed by soil bacteria in a two step processo First, ammonia or ammonium is converted to nitriteo Then, nitrite oxidizes into nitrate

● Bacteria gains energy through nitrification

● Fastest phase of cycle

● Occurs in lithosphere

Nitrification

● Plant roots absorb nitrate, ammonia, or ammonium, and incorporate their nitrogen into plant proteins and nucleic acids

● When animals consume plant tissues, they assimilate nitrogen by taking in plant nitrogen compounds (amino acids) and converting them to animal compounds (proteins)

● Slowest phase of the cycle

Assimilation

Ammonification● Conversion of biological nitrogen compounds into

ammonia (NH3) and ammonium ions (NH4+)

● Process○ Organisms produce nitrogen-containing waste products

(urea and uric acid)■ Contained in urine and wastes of birds

○ Those substances are decomposed■ Nitrogen is released into the abiotic environment in

the form of ammonia● Ammonifying bacteria facilitate this process● Ammonia → nitrogen cycle → nitrification and assimilation

● Reduction of nitrate (NO3-) to gaseous nitrogen (N2)

● Denitrifying bacteria-> reverse action of nitrogen-fixing & nitrifying bacteria by returning N2 into atmosphere○ live & grow where there is little to no free

oxygen (ex: deep soil near water table)

● Occurs in lithosphere

Denitrification

● Burning fossil fuels, the application of nitrogen-based fertilizers, and other activities can dramatically increase the amount of biologically available nitrogen in an ecosystem

● Where in cycle can humans affect it?○ Nitrogen availability can limit the primary productivity of many

ecosystems.○ Industrial nitrogen fixation has increased exponentially since the

1940s, and human activity has doubled the amount of global nitrogen fixation

● How can humans decrease effect?○ Decrease burning of fossil fuels

Human Effect on the Nitrogen Cycle

Nitrogen Cycle’s Use for Humans● Amino acids all contain nitrogen

○ make up the proteins in hair, muscles, skin, & other important issues

● Normal growth, cell replacement, & tissue repair all require nitrogen for production of new cells