Nitrogen Cycle
Nitrogen Fixation
Atomospheric nitrogen(N2) is converted to ammonia (NH3) by nitrogen-fixing bacteria in the soil
Bacteria from a mutualistic relationship (provide various different things to each other) wth leguminous plants by inhiting their root nodules
Leguminous plants are a famliy of plants like peas, beans
The bacteria provide a source of ammonium ions for the plants and the plant provides sugar to the bacteria
Free living bacteria like Azotobacter
Fix N2 into NH3 and then amino acids
When they die they are decomposed by saprobionts (decomposers)
Nitrogen-rich compounds are released and converted into a form that can be assimilated by plants
Abiotic Processes
Lightning
Artificial Fertilisers
Ammonification
When an organism dies or produces waste
it can be decomposed by saprobionts
This releases the nutrients contained inside
Saprobionts decompose the organisms biomass by extracellular digestion and inorganic ammonium ions are released into the soil
Ammonification is a by-product of saprobionts nutrition
Nitrification
Ammonium ions that are realised from ammonification are converted into nitrates by bacteria in the soil
Nitrifying bacteria (Nitrosomonas)convert ammunium ions into nitrites
Another bacteria (Nitrobacter) then convert nitrites into nitrates
Denitrification
Denitrifying bacteria convert nitrates in the soil back into atmospheric nitrogen (N2)
This takes place in anaerobic conditions
waterlogged soils
By anaerobic bacteria
Disruptions
Human activities like agriculture and the combustion of fossil fuels have significantly altered the natural nitrogen
Using fertilisers in agriculture leads to eutrophication (over-enriching the soil and water bodies.
Nutrient-rich soils favor fast-growing species (like nettles and certain invasive grasses) which aggressively outcompete delicate wildflowers adapted to poor soils.
Therefore the nitrogen cycle needs to be kept balanced to preserve our ecosystem and reduce biodiversity