2. The Soil Ecosystem

Question 1

What is soil? 3

Answer 1

1. Thin mantle over surface of earth 2. interface between gaseous atmosphere and rocky lithosphere 3. where terrestrial life is sustained

Question 2

Define lithosphere. 1

Answer 2

1. crust and upper layers of upper mantle of earth

Question 3

What are the abiotic components of soil? 4

Answer 3

1. Minerals 2. Water 3. Gas - spaces allow water, nutrients and other gases to travel and interact with organisms 4. Other nutrients

Question 4

What are the biotic components of soil? 3

Answer 4

1. Meso and macrofauna eg. oligochaetes, nematodes, athropods and molluscs 2. Microfauna ef. protozoa, algae, microbes 3. Viruses

Question 5

What are horizons in terms of soil? Include diagram. 7

Answer 5

1. Different layers/strata are called horizons
2. Horizon composition determines soil type
3. fresh litter is not decomposing, or is in early stages
4. Organic is decomposing matter
5. biotic material found in first 3 layers
6. huge global soil diversity

Question 6

Describe tropical soils. 4

Answer 6

1. very deep - large profile
2. old and weathered
3. little organic material, just a thin later on top
4. most biomass in first 3 cm and above

Question 7

Describe desert soils. 3

Answer 7

1. No organic component
2. minimal vegetation
3. weathered

Question 8

Describe tundra soils 5

Answer 8

1. arctic and antarctic
2. permafrost beneath thin soil layer
3. organically rish
4. not productive, can’t support much life due to temp
5. small growth window and little decomposition

Question 9

Describe british and mancunian soils. 5

Answer 9

1. range across britain
2. mancunian range from free-draining to quite wet
3. generally wet and acidic
4. can have raised or blanket peat bog soils
5. 2 soil types cover 60% of UK: brown earths and gley soils

Question 10

Describe brown earth soils. 6

Answer 10

1. general to well drained
2. moderately deep - good mixing between organic (F+H) and mineral (A) layers
3. found under temperate grasland and deciduous forest, also good for agriculture
4. high biotic activity, especially earthworms
5. high rates of decomposition and nutrient availability
6. brown colour form iron oxides (fe3+)

Question 11

Describe gley soils. 5

Answer 11

1. periodic water logging
2. mineral (B) horizon compact with few large pores
3. water logging leads to anaerobic conditions so less productive than brown earth soils
4. red markings indicate plant life due to oxidation of iron
5. generally blue green/grey from microbial reduction of ferric (fe3+) to ferrous (fe2+) iron

Question 12

Describe podzolic soils. 7

Answer 12

1. also important in uk
2. free draning, sandy parent material
3. beneath coniferous forest and heathland
4. very deep and acidic organic (F+H) horizon

5, acidic water leaches nutrients

6. Dark brown surface layer, bleached, nutrient poor organic horizon, and lower horison with iron, aluminium and other nutrients
7. low productivity, lacks earthworms

Question 13

How is parent material formed and how does it influence soil variation? 6

Answer 13

1. weathering of rock (biotic/abiotic)
2. mineral components (acidic/basic)
3. grain size (sand, silt or clay) impacts h20/nutrient availability
4. pH determines what can grow there
5. less acidic means more life
6. freeze-thaw or lichen colonization, which produces acid therefore erosion, can influence mineral layer

Question 14

What is the soil triangle? 2

Answer 14

1. Best growing soils are in the middle

Question 15

How does climate inflluence the variation of soils? 5

Answer 15

1. association between regional climates, vegetation and soil
2. less important in old soils eg. tropical (2m year old) and young soils eg. Britain 15 000yr old from glacial deposits
3. important in temperate areas
4. temp and rainfall impact - warmer and wetter means more decomposition, faster chemical reaction rates
5. biological growth rate doubles every 10 degrees until 35 degrees celcius

Question 16

How does topography influence the variation in soils? 4

Answer 16

1. moving downhill, water table rises compared to durface level
2. influences soils
3. less well draining approaching river
4. brown earths and podzoic soils become gley towards river

Question 17

How does time influence the variation in soils? 7

Answer 17

1. More weathering with age
2. more highly differentiated layers
3. leaching of minerals and nutrients downwards (podzolisation)
4. incrase of soil organic matter - why tropicals are so deep
5. more N, less phosphorous - both needed for plant growth
6. As animals colonize, N increased, then plataeu
7. Phosphorous levels increase, then bound into soil matrix so not available

Question 18

What is the composition of soil biota? 8

Answer 18

Question 19

How do plant roots affect the soil structure? 6

Answer 19

1. Anchor vascular plants
2. conduit for nutrients and water
3. grow about 2cm daily. pushing all soil particles and creating gaps
4. obligate requirement for aerobic conditions
5. Fix and secrete carbon - support other llife
6. secrete mucus and deposit cells, changing rhizosphere

Question 20

What is the rhizosphere? 5

Answer 20

1. Area of soil surrounding root that is affected by its activities
2. reduced water potential here as net flow towards roots, creating a nutrient gradient
3. Increased carbon changes ion composition and pH
4. Increased microbial abundance, providing food for protozoa
5. Causes increaed protozoa abundance

Question 21

How do fungi change the structure of the soil? 7

Answer 21

1. Dominant soil microbes (greater biomass than bacteria)
2. Grassland soils have about 250kg fungal hyphae per hectare
3. Less species rich than bacteria
4. most of biomass underground
5. hyphal structure facilitates colonization, utilisation and mobillisation of organic matter and nutrients
6. princple role in degradation of organic matter
7. symbiotic and pathogenic relationships with plants

Question 22

Why are bacteria important in the soil? 4

Answer 22

1. most numerous and diverse microbes in soil (10¹⁰-10¹¹/g soil)
2. limited mobility
3. degradation of organic matter by production of extracellular enzymes
4. important in element cycling, especially nitrogen

Question 23

What is the importance of soil in carbon cycling? 4

Answer 23

1. Most carbon is in lithospheric and aquatic deposits eg. caco3 in oceans
2. this is not acrive
3. soil contains most mobile carbon
4. also sound in atmosphere and live organisms

Question 24

What is the carbon cycle? 5

Answer 24

Question 25

What is primary productivity? 5

Answer 25

1. Rate at which energy from the sun is stored 2. Main contributers are plants, algae and cyanobacteria 3. main flux of carbon from atmoshphere to soil 4. variation wtih ecosystem 5. can be measured by measuring plant growth

Question 26

What are the differences in primary productivity between ecosystems? 6

Answer 26

1. Colder environments mean less carbon is fixed 2. less fixed in grass than trees 3. curring down forests releases carbon but more released by ploughing grassland which is done regularly for agriculture

Question 27

What is the nitrogen cycle? 5

Answer 27

Question 28

What is nitrogen fixation? 8

Answer 28

1. Process of making ammonia from elemental nitrogen 2. Nitrogen enters soil via lightening/bacteria 3. N₂ + 8H⁺ + 8e^- -\> 2NH₃ +H₂ 4. Can be symbiotic via nodules 5. Can be non-symbiotic by: 6. Obligate aerobes - need oxygen 7. Obligate anaerobes can't have oxygen 8. Facultative aerobes prefer oxygen but not essential

Question 29

What is nitrification? 4

Answer 29

1. Nitrates are the most bioavailable form of nitrogen 2. *Nitosomonas* spp: 2NH₃ + 3O_{2 ->} 2NO₂^- + 2H₂O + 2H⁺ 3. *Nitrobacter* spp: 2NO₂^- + O₂ -\> 2NO₃^- 4. Denitrification is the removal of oxygen from nitrogen compounds to make ammonia

Question 30

Fundamentals of Ecology, Odum and Barrett. 2005. Give some extra detail about the nitrogen cycle. 8

Answer 30

1. Breakinf down proteins to nitrates provides bacteria wiht energy 2. Creating proteins from nitrates requires energy input 3. Oxidation of ammonia to nitrites to nitrates provides bacteria with energy 4. Ammonium, nitrite and nitrate can be used by plants, but nitrate is more expensive as special enymes are required to convert it to ammonium 5. Some bacteria fix nitrogen in the ocean in temperate zones 6. May be free-living or symbiotic 7. Enzyme nitrogenase splites N₂ in n-fixation 8. Less efficient in terrestrial free living bacteria than symbiotic

Question 31

The Biology of Soil. R. D. Bardgett. 2005. What is the importance of parent material in determining soil properties? 3

Answer 31

1. Parent material can be from the rock below or sediments carried there 2. The rock determines the qualities and minerals of the soil 3. eg. basic larva soils are high in calcium, magnesium and posassium with fine texture - fertile brown earths

Question 32

The bIology of soil. R. D. Bardgett. 2005. How does climate influence the properties of soil? 3

Answer 32

1. Temperature and rain have a greater effect at high altitudes and latitudes. 2. Organic matter increases with latitude, until beyond the treeline, then declines 3. Decomposition reduced due to lower temp

Question 33

The biology of soil. R. D. Bardgett. 2005. How does topography influence the properties of soil? 2

Answer 33

1. Steep parts of hills have shallow soils 2. lower soils are finer as these particles are moved here by erosion

Question 34

the biology of soil. R. D. Bardgett. 2005. How is stable soil formed? 6

Answer 34

1. Freeze thaw/ shrinkage and swellig moulds soil 2. rain and ploughing reorganizes soil 3. burrowing animals mix organic and mineral horizons to create stable organo-mineral complexes 4. faeces aere centres for aggregate formation 5. roots and microbes produce slimes that hold everything together 6. aggregation and structure determine pore distribution