1.5 The Nitrogen Cycle

The Nitrogen Cycle - Big Picture

• The Nitrogen cycle is the movement of atoms and molecules containing the element nitrogen between sources and sinks

• The nitrogen cycle (like the carbon cycle) is a biogeochemical cycle, which is a self-regulating, naturally-occurring movement of chemical molecules through various sources and sinks (reservoirs)

• These cycles help stabilize and regulate the flow of matter through ecosystems

• The nitrogen cycle can be disrupted by human activity

The Importance of Nitrogen

• Nitrogen is vitally important in living things because it is a major component of amino acids and nucleic acids (the building blocks of proteins and DNA)

• Nitrogen is a limiting factor in ecosystems

  • A limiting factors is a resource that is scarce in an ecosystem, but is vital to its functioning

• Producers are the basis of the trophic structure of ecosystems, and producers need nitrogen to grow

  • Fertilizer contains nitrogen (and other elements) because of the addition of nitrogen enhances producer growth

The Nitrogen Cycle

1. Fixation: N2 is fixed by lightning (abiotic) or microbes in soil/root nodules (biotic)

2. Ammonification: NH3 converted to NH4 by soil bacteria living in the soil; NH3 can also be added by decay of organic material

3. Nitrification (two stages): NH4 converted to NO2, then NO3

4. Assimilation: NO3 uptaken by plants through roots (then to animals)

5. Denitrification: NO3 can be converted back to N2 by soil bacteria

Nitrogen Reservoirs

• The nitrogen cycle is primarily driven by microbial action (biotic)

• The atmosphere is the major reservoir of nitrogen (78% of gases in the troposphere)

• Unlike carbon, most reservoirs of nitrogen store the element for short periods of time. There are few substantial geologic stores of nitrogen