Nitrogen Processes

Question 1

What is the significance of nitrogen?

Answer 1

Essential nutrient for life.

Can be a limiting nutrient in soils/marine environments

Question 2

What form is nitrogen in in nature?

Answer 2

Organic forms.

e.g. Humic and fulvic acids, proteins, peptides, amino acids

Question 3

What are the two anaerobic chemoheterotrophic nitrogen processes?

Answer 3

Denitrification and Nitrate Ammonification

both nitrate reduction processes

Question 4

What is the anaerobic chemolithoautotrophic process?

Answer 4

Anammox bacteria

nitrogen oxidisation

Question 5

What is the aerobic chemolithoautotrophic process?

Answer 5

Nitrification

nitrogen oxidisation

Question 6

Describe denitrification

anaerobic chemoheterotrophy

Answer 6

Reducing nitrate to nitrogen gas.
NO3- > NO2- > NO > N2O > N2
+5 to 0 oxidation state.

PED = organic matter 
TEA = various forms of nitrogen (not O2)

Type of dissimilatory nitrate reduction.

Question 7

Describe Nitrate ammonification

anaerobic chemoheterotrophy

Answer 7

Reducing nitrate to ammonium/ammonia.
NO3- > NO2- > NH3

Type of dissimilatory nitrate reduction.

Question 8

Describe nitrification 
(aerobic chemolithoautotrophy)

Answer 8

Oxidising of ammonia to nitrate.
PED = NH4+
TEA = O2

NH4+ > NO2- > NO3-
-3 to +5 oxidation state.

Common in habitats with high ammonium.

Question 9

How does nitrification produce bioavailable nitrogen for plants?

Answer 9

Plants assimilate (take up) ammonia. 
At neutral pH, NH3 is NH4+, which is not readily avaible to plants. 
Nitrifying bacteria convert NH4+ to NO3- (which is not absorbed by clays (-ve charge) so can be assimilated by plants).

Question 10

Describe Anammox bacteria

anaerobic chemolithoautotrophy

Answer 10

Anaerobic ammonium oxidation
PED = NH4+
TEA = NO2-

NH4+ + NO2- -> N2 + 2H2O
Nitrogen is both the electron donor and acceptor.

Occurs in circumneutral to basic pH

Anammox bacteria can grow by anaerobic chemoheterotrophy, using organic C instead of ammonia. But will do anammox if no organic C.

Question 11

Describe Nitrogen fixation

Answer 11

Part of the dark reaction in photosynthesis.
Requires energy - 15 ATP per 1 nitrogen molecule fixed.

N2 + 6H+ + 6e- -> 2NH3

Doesn’t require O2.
Brings nitrogen back into water and soil. Whereas, denitrification and anammox volatilise N2.

e.g., Cyanobacteria (oxygenic photoautotrophs) and Rhizobia (chemoheterotrophs)

Question 12

Describe ammonification

Answer 12

Formation of ammonia from organic matter.
Organic matter have nitrogen in the already reduced form, so turning it from organic nitrogen to ammonium doesn’t change the oxidation state.