🌿 APES Topic 1.5: The Nitrogen Cycle

Nitrogen Cycle

The movement of nitrogen atoms and nitrogen containing molecules between sources and sinks.

Why Nitrogen Matters

Essential for all living things (proteins, DNA, chlorophyll) but atmospheric N2 is inert; its availability often limits plant growth.

Major Nitrogen Reservoirs

Atmospheric N2 gas, soil (inorganic and organic forms), living organisms, and water bodies.

Nitrogen Fixation

Converts atmospheric N2 into usable NH3 or NH4+.

Abiotic Fixation

Nitrogen in the atmosphere becomes NO or NO2 through lightning and cosmic radiation, forming HNO3 when combined with rain.

Biotic Fixation

Soil microorganisms convert N2 into NH3; some plants like legumes have root nodules for this process.

Nitrification

The process where ammonia or ammonium is converted to nitrites and then to nitrates by nitrifying bacteria.

Assimilation

Plants absorb nitrates or ammonium through roots; animals obtain nitrogen by consuming other organisms.

Ammonification (Deamination)

Decomposers break down organic nitrogen from dead matter into ammonium ions.

Denitrification

Nitrates are converted back to gaseous nitrogen by anaerobic denitrifying bacteria.

Haber-Bosch process

An industrial method to produce fertilizers that adds excess reactive nitrogen to ecosystems.

Eutrophication

A process caused by fertilizer runoff leading to algal blooms and dead zones in water bodies.

Reactive Nitrogen

Forms of nitrogen that are biologically available and can disrupt ecosystems if in excess.

Greenhouse Gas

Gases like N2O that trap heat in the atmosphere, contributing to climate change.

Consequences of Nitrogen Imbalance

Includes eutrophication, greenhouse gases production, and shifts in biodiversity.