EEMB 171 Cumulative

Question 1

Clay

Answer 1

Any mineral particle smaller than 2 μM

Question 2

Aluminosilicates

Answer 2

1. Layered
2. High surface area, particularly 2:1 clays
3. Electrically charged
4. Cation Exchange Capacity (CEC)

Question 3

Soil Organic Matter

Answer 3

Complex mix of plant debris, microbial products, humic material (fulvic, humic, humin). Behaves similarly to clays in many functional ways:

1. Structure
2. Water holding capcity
3. CEC

Question 4

Jenny State Factors

Answer 4

1. Climate
2. Organisms
3. Relief
4. Parent Material
5. Time
6. Humans

Question 5

NPP

Answer 5

Net Primary Productivity = Photosynthesis – Plant Respiration

Question 6

GPP

Answer 6

Gross Primary Productivity = Total ecosystem photosynthesis

Question 7

NEE

Answer 7

Net Ecosystem Exchange = NPP – soil respiration

Question 8

NEP

Answer 8

Net Ecosystem Productivity = GPP – soil respiration – leaching and harvest losses

Question 9

Liebig’s Law of the Minimum

Answer 9

• Growth is restricted by a single limiting factor
• Species can adapt to adjust allocation to reduce demand, increase supply- may be co-limited

Question 10

How does Liebig’s Law of the Minimum apply to communitiy growth?

Answer 10

Species adapted to low nutrients have low maximum growth rates, and may not be limited by nutrients, even at low nutrient supply. Fertilization will increase total community production through species replacement.

Question 11

WUE

Answer 11

Water Use Efficiency = g production / g H₂O used

Question 12

NUE

Answer 12

Nitrogen Use Efficiency = g production / g N used

Measured by N content of senesced material

Question 13

Tannins

Answer 13

C-rich defensive chemicals

• Produced when C is available and N is limiting
• Bind to proteins and make them undigestable

Question 14

Alkaloids

Answer 14

N-rich defensive chemicals produced by plants

Question 15

What are the four components of water potential?

Answer 15

1. Matric potential- from interactions with surfaces and capillary pores
2. Solute potential- from interactions with dissolved solutes
3. Gravitational potential
4. Pressure potential

Question 16

Fine textured soils will have a _____ water content at a given water potential.

Answer 16

higher

Question 17

Fine textured soils will have a _____ water potential at a given water content.

Answer 17

lower

Question 18

Field Capacity

Answer 18

The amount of water content held in soil after excess water has drained away and the rate of downward movement has materially decreased.

Question 19

Permanent Wilting Point

Answer 19

Point where plants wilt and die. Commonly defined as –1.5 MPa

Question 20

Available Water

Answer 20

= Field Capcity – PWP

Question 21

While _____ may be out of equilibrium with their environment and act as a conduit for water from
moist soil to dry atmosphere,
_____ must be in equilibrium with their environment.

Answer 21

plants; microbes

Question 22

Who is responsible for decomposition?

Answer 22

• Micro and Meso Fauna- break material down physically
• Microorganisms (bacteria and fungi) break material down chemically

Question 23

What is the equation for exponential decay?

Answer 23

dX/dt = -k X

Question 24

How does soil water content effect the rate of decomposition?

Answer 24

• At low water content, water availability limits decomposers
• At high water content, soils saturate and oxygen limits decomposition
• Water filled pore space integrates these effects, optimum at 60%

Question 25

An increase of 10 ºC increases the rate of decomposition by a rate of \_\_\_\_\_.

Answer 25

2-fold

Question 26

Describe the differences in N availability between fresh and aged litter.

Answer 26

* In fresh litter, most N is in proteins--easy to break down * In old material, N may be in complex structures--hard to break down

Question 27

SUE

Answer 27

Substrate Use Efficiency

Question 28

What is the sequence of decomposition?

Answer 28

1. Leaching of soluble material 2. Decomposition of free cellulose – net immobilization 3. Decomposition of lignin-cellulse complex- net mineralization

Question 29

What are the sources of SOM?

Answer 29

Leaf litter: 20-60%; Root death: 30-60%; Root exudates: 5-10%

Question 30

N-fixation

Answer 30

N₂ → NH₃ Importance: accounts for almost all N supplied to native ecosystems. * Only done by bacteria * Energetically expensive

Question 31

What are the types of N-fixing systems?

Answer 31

1. _Symbiotic_ (legume/rhizobium; actinorhizal) 2. _Associative_ (in rhizosphere) 3. _Free living_

Question 32

Denitrification

Answer 32

NO₃^- → NO, N₂O, N₂ ## Footnote ``` Importance: removes N from system, produces trace gases (NO, N<sub>2</sub>O). Anaerobic respiration (heterotrophs use NO<sub>3</sub><sup>-</sup> instead of O<sub>2</sub>). ```

Question 33

Nitrification

Answer 33

NH₄⁺ →NO₃^- ## Footnote Importance: NO₃^- is mobile and easily lost to ecosystems NO₃^- is more available for plant uptake Nitrification produces NO and N₂

Question 34

Net Mineralization

Answer 34

NM = Gross mineralization - gross immobilization

Question 35

What is a fundamental difference between the N cycle and the Phosporus cycle?

Answer 35

The main source of N is the atmosphere and N fixation. The main source of P is mineral weathering.

Question 36

Catena Theory

Answer 36

Variation in soil and ecosystem properties down slope.

Question 37

Riparian Zones

Answer 37

Variable riparian contribution: 1. Arid systems--flashy water flows, limited riparian zones 2. Humid systems--more fully developed riparian zones

Question 38

Telescoping Ecosystem Theory

Answer 38

Changes in resistance and resilience varies with the component of the stream system * Stream: resilient * Parafluvial * Hyporheic * Riparian: resistant

Question 39

What are 3 methods plants use to attain Phosphorus?

Answer 39

1. Phosphate enzymes via roots break down organic phosphate 2. Production of organic acids to solubilize Ca⁺ and prevent phosphorus binding 3. Arbuscular Mycorrhizae: form a symbiotic relationship whereby plants share carbon in exchange for phosporus

Question 40

AEC

Answer 40

Anion Exchange Capacity

Question 41

Slash and Burn Agriculture

Answer 41

A method in which plots of land are torched for the purpose of releasing bound phosphorus from living organisms and volatilizing Nitrogen, thus increasing the P/N ratio in otherwise phosporus limited areas.

Question 42

In what systems is phosporus availability the highest?

Answer 42

* Young soils * Neutral soils * OM rich soil * Soils low in metal oxides * → much of the temperate world

Question 43

In what systems is phosphorus availability the lowest?

Answer 43

* Old soils * Acidic soils * OM poor soils * Soils high in metal oxides * → much of the tropical world

Question 44

A mineral solution pH of ___ in soil creates optimal solubility conditions for Al, Fe and Ca.

Answer 44

≈ 6

Question 45

How do plants get their phosphorus in low P availability soils?

Answer 45

1. Increase growth per unit P (high P-use efficiency) 2. Reallocation of internal P (e.g. P resorption prior to leaf senescence → \> 80%) 3. Modify metabolism to bypass P-requiring steps

Question 46

How does PO₄^3- availability compare with the pH of soil solutions?

Answer 46

* Acid soils: Fe, Al phosphates limit * Alkaline soils: Ca phosphates limit

Question 47

Fe and Al ______ dissolve at low pH, thus causing what?

Answer 47

hydroxides; Increased Fe and Al concentrations in solution, which bind to phosporus and effectively decrease its availability.

Question 48

CEC

Answer 48

_Cation Exchange Capacity_: the maximum quantity of total cations, of any class, that a soil is capable of holding, at a given pH value, for exchanging with the soil solution.

Question 49

Steady State Ecosystem

Answer 49

An ecosystem in which the recycling of nutrients equals its biological uptake.