Lecture 28: Nutrient Cycling

Question 1

What are some ways that nutrients enter the ecosystem?

Answer 1

Physical weathering: physical breakdown of rocks
Chemical weathering: reactions that release soluble forms of the mineral elements
Biological weathering: plant roots, lichens

Question 2

How are soil horizons formed?

Answer 2

From weathering, accumulation of organic matter, and leaching (dissolved particles moving from high to lower layers)

Question 3

Explain the importance of phosphorus

Answer 3

• essential to energetics, genetics, and structure of living systems: atp, rna, dna, and phospholipid molecules
• not abundant in the biosphere
• limiting factor for freshwater aquatic primary production, not usually for terrestrial primary production

Question 4

Explain the importance of nitrogen

Answer 4

• critical component of key biomolecules: amino acids, nucleic acids, chlorophyll, hemoglobin
• biggest reservoir is the atmosphere
• can limit rates of primary production in both terrestrial and aquatic systems

Question 5

What are the five transformations of nitrgoen?

Answer 5

1. nitrogen fixation
2. immobilization
3. mineralization/ammonification
4. nitrification
5. denitrification

Question 6

Explain nitrogen fixation

Answer 6

converting atmospheric N into forms primary producers can use

Question 7

Define immobilization

Answer 7

conversion of mineral forms of N (ammonia, nitrate) into organic forms (proteins)

Question 8

Explain mineralization/ammonification

Answer 8

conversion of organic forms of N (proteins) into mineral forms

Question 9

Explain nitrification

Answer 9

conversion of organic forms of ammonium to nitrite to nitrate

Question 10

Explain denitrification

Answer 10

converting nitrate into N gas

Question 11

Explain the importance of carbon

Answer 11

• its gasses play a role in controlling global climate
• what makes molecules organic
• not a limiting nutrient

Question 12

What influences decomposition rates?

Answer 12

temperature, moisture, chemical composition of decaying matter, and chemical composition of environment