Lecture 6-9 - Communities and Change

Question 1

What are the 9 Principal Terrestrial Biomes?

Answer 1

1. Arctic Tundra
2. Boreal Forest/Taiga
3. Temperate Deciduous Forest
4. Temperate evergreen forest
5. Temperate shrubland
6. Temperate grassland
7. Desert
8. Tropical seasonal rainforest
9. Tropical rainforest
10. Mountain Biome

Question 2

What shape are the trees in the boreal forest region? Why?

Answer 2

Conical shape
- snow accumulation prevented so limbs do not break
- minimises exposure and transpiration
- vertical orientation of canopy limbs improves efficiency of energy capture in low angle light conditions

Question 3

Why are meristems of deciduous woody plants enclosed by buds?

Answer 3

• protects meristem from freezing
• leaves and flowers form in autumn but only expand the following spring and summer
• leaves drained of nutrients before they fall

Question 4

How do plants in temperate shrubland protect themselves during the summer? (part 1)

Answer 4

A sclerophyllous habit - small, waxy leaves to limit transpiration
- deep roots to access water
- limited size

Question 5

How do plants in temperate shrubland protect themselves during the summer? (part 2)

Answer 5

Dormancy - can be seeds in the topsoil layer OR using underground storage organs (bulbs)

Question 6

What causes the contrasting appearance of the temperate shrubland in the mild wet spring and the hot dry summer?

Answer 6

The switch between growth/ leaf development and dormancy/ leaf loss

Question 7

Which biome is in a constant state of change more than any other?

Answer 7

Dry Tropical Forest (Savanna)

Question 8

What is a shifting mosaic?

Answer 8

A continual shifting of forest habitats across the landscape as a result of seasonal fires and grazing herbivores

Question 9

Which biome has the greatest vertebrate biomass of any biome? Why?

Answer 9

Savanna
- seasonal monsoon rains cause a surge in soft leaf tissue production by tropical grass
- seasonal shifts in monsoon winds trigger mass herbivore migrations from dry to wet grasslands

Question 10

What are the aspects of soil that determine biome and habitat productivity?

Answer 10

• physical component (structural and chemical, water, temp)
• inorganic component (bedrock, weathering)
• organic component (fungi, animals, plants)

Question 11

What are the 5 regions in a soil profile?

Answer 11

1. Humus - decaying organic matter
2. Topsoil - humus/mineral/clay mix
3. Leached layer - sand and silt
4. Subsoil - clay and leached minerals
5. Regolith - bedrock, rocks

Question 12

What organic and inorganic matter determines soil fertility?

Answer 12

Inorganic - alumina-silicates, silica, calcium carbonate
Organic - raw decomposing material, humus

Question 13

What is mull organic matter? What are its characteristics?

Answer 13

most fertile soil
- good aeration and temp
- rapid cycling of organic material
- abundance of microbes

Question 14

What is mor organic matter? What are its characteristics?

Answer 14

least fertile soil
- forms in less favourable conditions
- OM accumulates and acidifies (leaching)
- few decomposers

Question 15

In what ways does soil pH impact fertility and biodiversity?

Answer 15

• nutrient availability decreases as soil acidity increases
• this directly impacts a plant’s ability to source essential nutrients for growth and reproduction
• impact of soil acidity can be seen in the Arctic Tundra where fewer plant species survive in lower pH soils than neutral soils

Question 16

Why are aerobic microbes a key link between soil inorganic and organic fractions?

Answer 16

• Nitrogen cycling - the universal limiting factor for organic growth in soils

Question 17

What components are key to aeration and water mobility

Answer 17

Physical structure and anion/cation balance

Question 18

What are principal sources of energy for microbes?

Answer 18

Microbial oxidation of organic matter (OM) and complex organic compounds

Question 19

What is net mineralisation?

Answer 19

Occurs when more nutrients are released than can be taken up and utilised by soil microbes – this increases nutrient availability for plants
Temperate alkaline soils

Question 20

What is net immobilisation?

Answer 20

Occurs where addition of OM provides energy for microbes to utilise most of the nutrients produced by decomposition – leading to reduced availability for plants (high energy, low nutrients, all nutrients used)
Temperate acid soils

Question 21

What are the characteristics of healthy soil?

Answer 21

• equal balance between carbon and nitrogen components (C:N ratio) and N cycle is stable - N neither in surplus or deficit
• C:N = 20:1 - 30:1