Midterm 3

Question 1

Ammonia

Answer 1

NH3
Gas or soluble
Oxidation number -3

Question 2

Ammonium

Answer 2

NH4+
Soluble
Oxidation number -3

Question 3

Nitrate

Answer 3

NO3-
Soluble
Oxidation number +V

Question 4

Nitrite

Answer 4

NO2-
Soluble
+3

Question 5

Nitrogen

Answer 5

N2
Gas or soluble
0

Question 6

Describe organic forms of nitrogen

Answer 6

1. Nitrogen contained in SOM occurs as a wide range of compounds
2. Amino acid-N is most abundant

Question 7

How much N is contained in microbial biomass and list the C/N ratio for fungal and bacterial cells.

Answer 7

5-10% of total soil N is contained in microbial biomass. Fungal cells have a C/N ratio of 10:1 and bacterial cells have a C/N ratio of 4:1.

Question 8

Immobilization

Answer 8

NH4/ammonium and NO3-/nitrate into organic N (amino acids).

Question 9

Ammonification

Answer 9

Conversion of organic N compounds into ammonium (NH4+).

Question 10

Nitrification

Answer 10

Ammonium (NH4+) oxidation to nitrite and nitrate (NO2- and NO3-).

Question 11

Denitrification

Answer 11

Reduction of nitrate (NO3-) to nitrogen gas (N2). Several intermediates are involved.

Question 12

Gross N mineralization

Answer 12

The total amount of organic nitrogen converted into inorganic forms (primarily ammonium) through microbial activity in the soil over a given period.
(Overall potential)

Question 13

Net mineralization

Answer 13

The amount of inorganic nitrogen (e.g., ammonium) remaining in the soil after accounting for microbial uptake and other processes like immobilization.
(What’s available)

Question 14

What are the three inorganic forms of sulfur?

Answer 14

Elemental sulfur, sulfides, SO42-, sulfur dioxide

Question 15

What are the organic forms of sulfur?

Answer 15

They are found in amino acids and esters stored in microbial biomass.

Question 16

What are four key points about sulfur immobilization?

Answer 16

1. Sulfate is converted into sulfur containing biomolecules by microbes, plants, and animals
2. Can occur in aerobic or anaerobic conditions
3. Sulfur is stored in microbial biomass as amino acids
4. Sulfate is converted into a sulfur containing protein called PAPS

Question 17

What are the two pathways for sulfur mineralization?

Answer 17

1. Biological - Microbial activity converts organic into inorganic sulfur. Driven by a need for C.
2. Biochemical - Enzymes cleave C-O-S bonds, completed by inter/intra cellular sulfatase. Driven by a need for S.

Question 18

What does “mineralization of S is driven by a need for carbon” mean?

Answer 18

Microbes break down organic matter containing sulfur in order to access carbon as an energy source. This process creates inorganic sulfur in the form of sulfate SO42-.

Question 19

Discuss sulfur oxidation

Answer 19

Sulfur-OB’s oxidize sulfur to create SO42- or sulfuric acid which occurs because of the hydrogen ions released during this process. The release of H+ then decreases pH which causes the acidification of soils. This process may be abiotic or microbial in aerobic zones and microbial in anerobic.

Question 20

What are the two steps in nitrification?

Answer 20

1. Ammonium oxidation: Ammonium (NH4) to nitrite (NO2)
2. Nitrite oxidation: Nitrite (NO2) to (NO3)

Question 21

What is the intermediary in nitrification?

Answer 21

Hydroxylamine which is converted into nitrite between ammonia and nitrite.

Question 22

What two enzymes are involved in nitrification?

Answer 22

1. During step 1, ammonia monooxygenase is involved
2. During step 2, nitrite oxidoreductase is involved