Nitrogen Cycle Flashcards
What is nitrification?
Ammonia - Nitrite - Nitrate
Highly aerobic
What is ammonium oxidation?
Transforming ammonia into nitrite
Net energy gain of hydrogen ions and two electrons
AMO and HAO are the enzymes involved
Creates hydroxylamine and water in the middle
Where does ammonium oxidation take place?
In the periplasm of bacteria
What is nitrite oxidation done by?
Nitrite oxidier organism
Uses the enzyme NOX/NXR
Little energy gained in the process
Why is nitrification important?
Nitrate is more mobile in soils - risks leaching
Nitrate can be used as a substrate for denitrification - risk N2O emissions
Nitrification releases N2O directly
What are denitrifiers?
Facultative anaerobes that use nitrogen oxides to maintain respiration when oxygen is limiting
What is the spatial structuring of soil?
Made of many soil aggregates that stick together tightly
Have pores that can be air or water filled
Large pores = more air so aerobic
Small pores = less air so anaerobic
Can have aerobic and anaerobic respiration happening at the same time in different places - spatial change
Soil is always changing over time due to oxygen availability fluctuations and change in weather - temporal change
What are the denitrifying enzymes?
Nitrate reductase
Nitrite reductase - always for denitrification
Nitric oxide reductase - if expressing this then will always be expressing nitrite reductase
Nitrous oxide reductase
How do N2O fluxes change after fertiliser is added?
Peaks of N2O emission after fertilisation
Also increases after harvest and tillage
What was concluded about N2O emissions after they added fertiliser to crops?
Large increase in emissions associated with fertiliser application
High organic carbon content causes more emissions than less fertile soils
Fine texture restricted draining soils along with neutral to slightly acidic soils had larger emissions (more anaerobic respiration in finer soils)
What percentage of water filled pore space caused nitrification and denitrification?
<60% = nitrification
> 60% = denitrification
Denitrification becomes more dominant as soil gets wetter
What causes N2O emissions from denitrification?
Occurs if denitrification is incomplete
Lack of nitrous oxide reductase activity (due to soil condition and soil community structure differences)
What denitrification genes were the most common?
NirS and NirK
What denitrification gene is the least common?
NosZ
No NosZ means no reduction of N2O so it will be released into the atmosphere
How does soil community change as soil becomes more anaerobic?
NirS responds more to anaerobic conditions
More denitrification causes communities to change to be more denitrification dominant - drives community towards N2O emissions
So will release more N20 then use it
Simulates agriculture
