Lecture 16

Question 1

How many carbon atoms do microorganisms need to build biomass

Answer 1

8C : 1N

24 C microbes needed to find 1 N to build biomass

Question 2

Define decomposition

Answer 2

Chemical Rxn occurring during decay of plant/animal remains

Altered chemical composition produces energy

Question 3

Define Mineralization

Answer 3

Release of soluble or gaseous inorganic constituents during decomposition

Question 4

What does SOC release during mineralization

Answer 4

CO2

Question 5

What does SON release during mineralization

Answer 5

NH4

Question 6

Define Humification

Answer 6

Decomposition results in black, greasy OM

Question 7

What was the old theory of Humification

Answer 7

Condensation Rxn: low MW biopolymer becomes high MW biopolymer

Question 8

What is the new theory of Humification

Answer 8

Stabilization of SOC by three mechanisms

Question 9

What are 5 Non-humid substances

Answer 9

1. Cellulose
2. Hemi-cellulose
3. Lignin
4. Lipids
5. Protein

Question 10

What is cellulose

Answer 10

Linear polymer of glucose units
~30% of plant material

Question 11

What is Hemi-cellulose

Answer 11

Branched polymer of different sugars
~20% plant material

Question 12

What is lignin

Answer 12

Branched, aromatic polymer
~20% of woody plant material

Question 13

What are Lipids

Answer 13

Fats, waxes
~20% cellular material

Question 14

What is protein

Answer 14

-amino acids (N is present)
-Biochemical “machine”
-5% plant material

Question 15

Decomposition gradient of non humid substances (easiest to hardest to decompose)

Answer 15

Protein > Hemicellulose > Cellulose > Lignin > Fats

Question 16

What is the historic method for examining soil fertility

Answer 16

Humic fractions

Question 17

What do microbes use to cleave off functional groups

Answer 17

Enzymes

Question 18

What are the 3 limits for decomposition

Answer 18

1. Size of molecule
2. Aggregate
3. Mineral associated organic matter

Question 19

What is the soil carbon model

Answer 19

Plant Animal Residue > Soil > Microbe Enzymes > Energy Biomass > SOM stability

Question 20

What is mean residence time

Answer 20

-time of atoms to cycle through pools
-plant residue: biopolymers, some chemical resistance

Question 21

What are the 3 SOM Theoretical Pools

Answer 21

-Chemical Protection
-Physical Protection (aggregation)
-Organo-mineral associations

Question 22

What carbon source do Autotrophs use

Answer 22

CO2

Question 23

What carbon source do Heterotrophs use

Answer 23

Org.C

Question 24

What Energy Source do photoautrophs use

Answer 24

Suns energy

Question 25

What energy source do chemoautotrophs use

Answer 25

Energy from organic C

Question 26

What energy do lithoautrophs use

Answer 26

Energy from soil REDOX Rxn