The Nitrogen Cycle

Nitrogen Cycle

N2

atmosphere

lightning fixed Fertilizer Factory

Denitrifying bacteria

Nitrates

Plants Bacteria

Decay &Waste

Animals Ammonia

Decomposers

Bacteria in Nodules

Nitrogen Facts• Nitrogen is necessary for life• Essential for proteins and DNA• Circulates through biotic and abiotic systems• Found in fertilizer with potassium and phosphorus• Plants use nitrogen for growth.• Earth’s atmosphere is 80% nitrogen gas (N2).• Nitrogen gas is a form that very few organisms can use

(they can’t absorb it directly).• In order to be used by organisms, nitrogen gas must be

“fixed”

• Nitrogen Fixation• Conversion of nitrogen gas in the atmosphere to ammonia

(NH4) by adding oxygen is done by nnitrogen fixing bacteria (rhizobia) use special enzymes to fix nitrogen (react the nitrogen with oxygen or hydrogen).

• Lightning provides enough energy to "burn" the nitrogen and fix it in the form of nitrate, NO3

- by adding oxygen

(this process is duplicated in fertilizer factories to produce nitrogen fertilizers).

3 Steps of the Nitrogen Cycle

Nitrogen Cycle continued:

Nitrification

• -conversion of ammonia to nitrates (chemicals of nitrogen and oxygen)

• -done by nitrifying bacteria

Nitrogen Cycle continued:

Denitrification

• -conversion of nitrates to nitrogen gas

• -done by denitrifying bacteria

The Nitrogen Cycle Explained

1. Fixed nitrogen can be absorbed by plants as ammonium (NH4

+), or it can be converted into nitrate (NO3

-) by nitrifying bacteria.

2. Most plants can take up nitrates and convert it to amino acids and then possibly proteins.

3. Animals acquire all of their amino acids when

they eat plants (or other animals).

4. When plants or animals die (or release waste) the nitrogen is returned to the soil.

5. The nitrogen that is usually returned to the soil in animal wastes or in the output of the decomposers, is ammonia (NH3). Ammonia is rather toxic.

6. Nitrifying bacteria in soil or water convert ammonia (NH4

+) to nitrates (NO3-), which are

taken up by plants to continue the cycle.

7. The final step to complete the nitrogen cycle is completed by denitrifying bacteria which convert nitrates (NO3

-) back into atmospheric nitrogen gas (N2) in order to return it to the air.

Ecosystem can experience nitrogen overload

This can happen by...

1. adding fertilizer

-increases plant growth

2. growing larger crops

3. burning fossil fuels

-releases nitrogen-containing chemicals into air that re-enter cycle

Effects of Nitrogen Overload:1. Soils-nitrogen saturation occurs, leading to

run-off & water pollution; this damages roots and stunts growth, and increases soil acidity, which kills soil organisms.

2. Atmosphere-nitric acid falls to Earth as acid rain, which kills fish, birds, amphibians, and trees.

3. Fresh Water-increase in nitrates increases algae & weeds and we get eutrophication (build up of nutrients); this harms drinking water, and reduces human body’s ability to carry oxygen to cells (anaemia)

4. Marine Ecosystems -algal blooms cause a “Red Tide”, oxygen gets used up and reduces life.

5. Biodiversity-as extreme conditions (temperature, acidity, precipitation) increase, biodiversity decreases