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Ecology and Ecosystems > 12-14: Soils > Flashcards

12-14: Soils Flashcards

1
Q

What percentage of land is moderately to highly degraded?

A

33%

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2
Q

How many tons of topsoil are lost every year to erosion?

A

25-40 billion tons

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3
Q

How much of Earth’s diversity is found below ground?

A

A quarter

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4
Q

What are the 4 main components of soil biodiversity?

A

Microflora
Microfauna
Mesofauna
Macrofauna

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5
Q

What is microflora?

A

Bacteria
Archaea
Fungi

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6
Q

What is microfauna?

A

Body width <0.1mm
Nematodes
Protozoa

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7
Q

What is mesofauna?

A

Body width 0.1-2mm
Microarthropods
Enchytraeids

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8
Q

What is macrofauna?

A

Body width >2mm
Worms
Termites
Millipedes

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9
Q

What role does the microbial biomass have in soil?

A

Break down complex organic material using extra-cellular enzymes
Nutrient transformation- available for plants
Symbiotic relationships- eg. N fixation in mycorrhizal fungi

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10
Q

What is mycorrhizal fungi?

A

Root associated microbe
Hyphae take up nutrients and increase root span for plants
Get C in exchange

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11
Q

What are Nitrogen fixers?

A

Can be free living or root associated
Prokaryotes that use nitrogenase to convert atmospheric N2 to ammonia
Called rhizobia

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12
Q

What are nematodes?

A

Microfauna
Aquatic roundworms
Most abundant of all soil fauna
50-100 species in UK grassland/forest

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13
Q

What are protozoa?

A

Microfauna
Single cell eukaryotes
Rely on the water in soil to move
Three types- flagellates, amoebae, ciliates
Produce cysts to survive in unfavourable conditions

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14
Q

What are microarthropods?

A

Mesofauna
Mites/collembolans
Fungal feeders and predatory

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15
Q

What are enchytraeid worms?

A

Mesofauna
Dominant in acidic peat soil
More of these in peak district than cows and sheep!

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16
Q

What are earthworms?

A

Macrofauna
Intolerant to acidity- replaced by enchytraeid worms in pH under 5.5
Over 80% total animal biomass in neutral soils

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17
Q

Physical properties of soil

A

Porosity- pore neck sizes dictate movement and animals, as mainly live in pore spaces
Water- water films are habitat for bacteria and protozoa
Temperature- rate of enzyme reactions, temp tolerances
pH- tolerance, eg. enchytraeid worms

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18
Q

What is the Rhizosphere effect?

A

Zone immediately touching the roots is the most biologically active
Called the zone of rhizodeposition

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19
Q

What are the two types of soil?

A

Mull

Mor

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20
Q

What is mull?

A 
Found in deciduous forest
High litter N
Low lignin and phenolics
Fertile, neutral pH soils
High bacteria and earthworms
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21
Q

What is mor?

A 
Found in coniferous forest
Low litter N
High lignin and phenolics
Infertile, acid pH soils
High fungi, microarthropods and enchytraeids
22
Q

What soils do you get below tree crown?

A

Organic nutrients
High fungal biomass
Low microbial biomass
Slower nutrient cycling

23
Q

What soils do you get outside of tree influence?

A

Inorganic nutrients
High NO3-
High bacterial and microbial biomass
Faster nutrient cycling

24
Q

What happens to C and N as trees get older?

A

Increases

25
Q

Wherever you go, how many organisms will be the same in the soil?

A

A third

26
Q

How many soil families are there?

A

909

Eg. clay, sandy, organic etc

27
Q

How many soil families are classed as rare?

A

332

28
Q

How many soil families are endangered/extinct?

A

88 endangered

17 extinct

29
Q

Examples of things damaging soils

A 
Introduction of invasive species
Soil sealing (building over land)
Climate change
Organic matter decline
Extensive human exploitation
30
Q

What does increasing land use intensity do?

A

Decrease diversity in soil functional groups (eg. earthworms)
Decrease the average number of trophic levels in the soil food web

31
Q

3 theories of what would happen if a species was lost

A

Redundancy hypothesis
Rivot hypothesis
Idiosyncratic hypothesis

32
Q

What is the redundancy hypothesis?

A

Can lose a species as long as there are others that can do the same job

33
Q

What is the rivot hypothesis?

A

All species have a role
If you lose one, there will be a drop in function
If you lose too many, the whole system will collapse

34
Q

What is the idiosyncratic hypothesis?

A

It depends on which species you lose- some have a bigger impact

35
Q

According to Jones et al., what are the 2 types of organisms that alter ecosystem processes?

A

Keystone species

Engineer species

36
Q

What are keystone species?

A

Alter material transfer via trophic relations
Impact on community composition
Eg. Enchytraeid worms

37
Q

What are engineer species?

A

Influence ecosystem processes through physical disturbance

Eg. moles and earthworms

38
Q

What hypothesis does Jones et al. support?

A

Idiosyncratic

39
Q

Diversity experiments in boreal forest results

A

Grew birch in sterilised soil
Added microbes to some
Increased growth and nutrient content when microbes present
Fewer fungal taxa = slower rate of decomposition and lower N availability in soil
Significant decline if under 10 species
Supports REDUNDANCY theory

40
Q

Ecotron experiment and results

A

Manipulated the complexity of soil systems
Less simplistic than boreal forest one
3 systems, one with microfauna, one with micro and mesofauna, one with micro, meso, and macrofauna
No detectable effect of soil biodiversity on aboveground plant productivity- REDUNDANCY
After 9 months, different plants growing in different soils- affects plant community

41
Q

Microbial diversity driving multifunctionality experiment and results

A

Tested in field
Soil samples from most major ecosystem types
Assessed bacterial and fungal diversity, measured soil functions eg. nutrient cycling
Multifunctionality index calculated
Abiotic and biogeographic factors found to be as important as microbial diversity
Positive relationship between bacterial diversity and eco. multi.
Lose diversity of soil = decline in system function

42
Q

Abiotic factors in plant communities

A

Moisture, temperature
Competition for nutrients, light, water, space
Allelopathy
Dispersal

43
Q

What is allelopathy?

A

Chemical inhibition of one plant by another due to release of substances acting as germination/growth inhibitors

44
Q

2 major pathways of soil feedback

A

Direct- via root herbivores, pathogens, symbionts

Indirect- through effect of soil decomposer subsystem on supply of nutrients

45
Q

What was the arbuscular mycorrhizal fungi experiment by Grime et al?

A

Used a mesocosm- outdoor experiment system, natural environment under controlled conditions
Looked at 20 species in a developing community
Reducing dominant grasses and increasing herbs increases diversity
Some with AM, some without
After 6 months, +AM 50% herb seedlings survive vs -AM 18%
+AM 23% were over 5mm height, -AM was 0%
So AM fungi promotes plant diversity

46
Q

What was the Van der Heijden et al experiment?

A

Different AM fungi induce different growth responses in plants- species specific
Manipulated AM species in grassland (mesocosm)
Each plot had randomly selected AM from pool of 23 species, gradient of 1 to 14 species
Each replicate had different combinations of AM, so effects were independent of which species added
Found that AM diversity enhances plant diversity and productivity
Increased AM diversity = greater P uptake by plants, enhanced plant biomass
AM diversity promotes ecosystem function

47
Q

Root pathogen experiment by Van der Putten et al.

A

Looked at the 3 coastal succession zones- marram grass is first, degraded and replaced, then changes as closer in land
Theory that degraded marram grass is associated with the build up of host specific pathogens in stable dunes
Festuca (another plant) is favoured when marram is exposed to soil pathogens
Planted Ammophila and Festuca in sterilised vs unsterilised soil
Transplanted soil of each species
Growth of ammophila was lower in unsterilised than sterilised soil
Growth of festuca was not reduced in unsterilised soil from ammophila
Ammophila was out-competed by festuca in non-sterilised soil
So soil pathogen-driven competition is an important mechanism in the succession of fordune vegetation

48
Q

Invasiveness of plant species experiment by Klironomos

A

Theory that rare plants accumulate pathogens that limit their growth
Highly invasive plants modify soil biota to promote their growth
Found that rare plants show negative feedback in own soil, whereas invasive show positive- ie. invasive perform better in own soil, rare perform worse (compared to other soils)

49
Q

How can you break the cycle of pathogen accumulation?

A

Crop rotation

50
Q

Bardgett et al plant nutrient cycling experiment

A

Parasitic plants stimulate microbial activity and nutrient cycling
Hayrattle infects fast-growing grasses, reducing their competitive dominance
Root death and C leakage = stimulates microbes
So enhanced N cycling and plant N supply
More nutrients! But bad for farmers as less grass for livestock

51
Q

Northup et al plant nutrient cycling experiment

A

Theory that tannic acid production from pine litter controls N release as organic N- used by dominant pine trees
Tannins enhance production of dissolved organic nitrogen (DON), inhibit availability of inorganic N
Pine trees control soil N availability to benefit their growth and competitive ability in N limited ecosystems

52
Q

Bowman et al plant nutrient cycling experiment

A

How slow-growing herbs and fast-growing grass coexist in alpine meadows
Herb increases soil microbial activity, less N available

Ecology and Ecosystems (4 decks)

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