Ecosystem Processes

Question 1

What are the 3 subsystems of an ecosystem?

Answer 1

The herbivore subsystem, the plant subsystem and the decomposer subsystem.

Question 2

What % of NPP is above ground in forests?

Answer 2

10%

Question 3

What % of above ground NPP in forest enters the herbivore subsystem?

Answer 3

5%

Question 4

What % of NPP is above ground in grassland?

Answer 4

Up to 50%

Question 5

What % of above ground NPP in grassland enters the herbivore subsystem?

Answer 5

25%

Question 6

What makes up humin?

Answer 6

Soil components not soluble in alkali.

Question 7

What makes up humic acids?

Answer 7

Soil components soluble in alkali and insoluble in acid.

Question 8

What makes up fulvic acids?

Answer 8

Soil components soluble in alkali and soluble in acid.

Question 9

Why is humus important?

Answer 9

Acts as a nutrients pool, maintains soil structure and provides water holding capacity.

Question 10

What are the 4 main processes in decomposition?

Answer 10

Leaching + volatilisation.
Comminution.
Non-enzymatic chemicals.
Catabolism.

Question 11

Define leaching.

Answer 11

Water passing through/over resources and the subsequent removal of nutrients.

Question 12

Define volatilisation.

Answer 12

The evaporation of oils, waxes and resins. Only significant in certain plant matter.

Question 13

Define comminution.

Answer 13

The breaking up of resources into smaller parts.

Question 14

What are some examples of non-enzymic chemical processes?

Answer 14

Cellulose oxidation by sunlight.
Weakening of chain bonds by UV.
Degradation by weak acids.

Question 15

What organisms perform catabolism?

Answer 15

1-15% is invertebrate based; the majority is microbial.

Question 16

How can you estimate decay rate?

Answer 16

By measuring: weight loss, density change, O2 consumption, CO2 evolution etc.

Question 17

What factors affect decay rate?

Answer 17

Temperature.
Water regime.
Actual evapotranspiration.
Resource quality.

Question 18

How does temperature affect decay rate?

Answer 18

Higher temperatures result in higher decay rates but there is a ceiling.

Question 19

How does water regime affect decay rate?

Answer 19

Highest decay rate occurs when the water regime is balanced.

Question 20

How does resource quality affect decay rate?

Answer 20

Lignins + polyphenols inhibit enzyme activity. Phosphorus + nitrogen increase resource quality.

Question 21

How does the C:nutrient ratio change as decay proceeds?

Answer 21

It changes to favour nutrients - CO2 is lost as decay proceeds.

Question 22

How does nitrogen content inhibit decay?

Answer 22

High and low nitrogen content inhibit decay. High nitrogen content means microbes don’t need to decay as much litter.

Question 23

When are nitrogen and phosphorus released during decay?

Answer 23

As a result of invertebrate grazing and mycelial antagonism (conflict between fungi).

Question 24

What is the most oxidised form of carbon?

Answer 24

CO2

Question 25

What is the most reduced form of carbon?

Answer 25

CH4

Question 26

What is the most oxidised form of nitrogen?

Answer 26

NO3-

Question 27

What is the most reduced form of nitrogen?

Answer 27

NH4+

Question 28

Define annamox.

Answer 28

Oxidisation of ammonium to dinitrogen gas.

Question 29

What are nitrogenases and where are they produced?

Answer 29

Enzymes produced by cyanobacteria that reduce nitrogen to ammonia.

Question 30

What is the function of nitrate reductase?

Answer 30

To reduce NO3- to NO2-.

Question 31

Define primary productivity.

Answer 31

Rate at which biomass is produced per unit area by plants.

Question 32

Define gross primary productivity.

Answer 32

The total fixation of energy by photosynthesis.

Question 33

Define autotrophic respiration.

Answer 33

The proportion of energy fixed by photosynthesis that is lost by respiration.

Question 34

Define net primary productivity.

Answer 34

The difference between GPP and Ra - the actual rate of production of new biomass available for heterotrophic organisms.

Question 35

What are the 2 opposing processes that drive the organic carbon cycle?

Answer 35

Photosynthesis and respiration.

Question 36

Describe the latitudinal trend in primary productivity.

Answer 36

Higher latitudes have lower mean primary productivity. This somewhat reverses underground.

Question 37

Define autochthonous organic matter.

Answer 37

Organic matter produced by photosynthesis within an ecosystem's boundaries.

Question 38

Define allochthonous organic matter.

Answer 38

Organic matter imported from outside the ecosystem.

Question 39

What is the production/biomass ratio?

Answer 39

The rapidity with which living material can replace itself.

Question 40

Define net ecosystem productivity.

Answer 40

The difference between GPP and total ecosystem respiration.

Question 41

Give examples of factors that limit productivity.

Answer 41

Inefficient use of solar energy. Water availability. Temperature.

Question 42

What is a constitutive plant defence?

Answer 42

A defence always present in the plant.

Question 43

What is an induced plant defence?

Answer 43

A defence produced or mobilised to where a plant has been injured.

Question 44

What is the carbon nutrient balance model (CNBM)?

Answer 44

The theory that the carbon-nutrient status of plants (determined by resource availability) controls the allocation of secondary metabolites.

Question 45

What are feeding inhibitors?

Answer 45

Compounds in plants that control decomposition rate.

Question 46

Define turnover time.

Answer 46

The period of time during which certain materials remain within a particular system.