12-14: Soils Flashcards
What percentage of land is moderately to highly degraded?
33%
How many tons of topsoil are lost every year to erosion?
25-40 billion tons
How much of Earth’s diversity is found below ground?
A quarter
What are the 4 main components of soil biodiversity?
Microflora
Microfauna
Mesofauna
Macrofauna
What is microflora?
Bacteria
Archaea
Fungi
What is microfauna?
Body width <0.1mm
Nematodes
Protozoa
What is mesofauna?
Body width 0.1-2mm
Microarthropods
Enchytraeids
What is macrofauna?
Body width >2mm
Worms
Termites
Millipedes
What role does the microbial biomass have in soil?
Break down complex organic material using extra-cellular enzymes
Nutrient transformation- available for plants
Symbiotic relationships- eg. N fixation in mycorrhizal fungi
What is mycorrhizal fungi?
Root associated microbe
Hyphae take up nutrients and increase root span for plants
Get C in exchange
What are Nitrogen fixers?
Can be free living or root associated
Prokaryotes that use nitrogenase to convert atmospheric N2 to ammonia
Called rhizobia
What are nematodes?
Microfauna
Aquatic roundworms
Most abundant of all soil fauna
50-100 species in UK grassland/forest
What are protozoa?
Microfauna
Single cell eukaryotes
Rely on the water in soil to move
Three types- flagellates, amoebae, ciliates
Produce cysts to survive in unfavourable conditions
What are microarthropods?
Mesofauna
Mites/collembolans
Fungal feeders and predatory
What are enchytraeid worms?
Mesofauna
Dominant in acidic peat soil
More of these in peak district than cows and sheep!
What are earthworms?
Macrofauna
Intolerant to acidity- replaced by enchytraeid worms in pH under 5.5
Over 80% total animal biomass in neutral soils
Physical properties of soil
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
What is the Rhizosphere effect?
Zone immediately touching the roots is the most biologically active
Called the zone of rhizodeposition
What are the two types of soil?
Mull
Mor
What is mull?
Found in deciduous forest High litter N Low lignin and phenolics Fertile, neutral pH soils High bacteria and earthworms
What is mor?
Found in coniferous forest Low litter N High lignin and phenolics Infertile, acid pH soils High fungi, microarthropods and enchytraeids
What soils do you get below tree crown?
Organic nutrients
High fungal biomass
Low microbial biomass
Slower nutrient cycling
What soils do you get outside of tree influence?
Inorganic nutrients
High NO3-
High bacterial and microbial biomass
Faster nutrient cycling
What happens to C and N as trees get older?
Increases
Wherever you go, how many organisms will be the same in the soil?
A third
How many soil families are there?
909
Eg. clay, sandy, organic etc
How many soil families are classed as rare?
332
How many soil families are endangered/extinct?
88 endangered
17 extinct
Examples of things damaging soils
Introduction of invasive species Soil sealing (building over land) Climate change Organic matter decline Extensive human exploitation
What does increasing land use intensity do?
Decrease diversity in soil functional groups (eg. earthworms)
Decrease the average number of trophic levels in the soil food web
3 theories of what would happen if a species was lost
Redundancy hypothesis
Rivot hypothesis
Idiosyncratic hypothesis
What is the redundancy hypothesis?
Can lose a species as long as there are others that can do the same job
What is the rivot hypothesis?
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
What is the idiosyncratic hypothesis?
It depends on which species you lose- some have a bigger impact
According to Jones et al., what are the 2 types of organisms that alter ecosystem processes?
Keystone species
Engineer species
What are keystone species?
Alter material transfer via trophic relations
Impact on community composition
Eg. Enchytraeid worms
What are engineer species?
Influence ecosystem processes through physical disturbance
Eg. moles and earthworms
What hypothesis does Jones et al. support?
Idiosyncratic
Diversity experiments in boreal forest results
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
Ecotron experiment and results
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
Microbial diversity driving multifunctionality experiment and results
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
Abiotic factors in plant communities
Moisture, temperature
Competition for nutrients, light, water, space
Allelopathy
Dispersal
What is allelopathy?
Chemical inhibition of one plant by another due to release of substances acting as germination/growth inhibitors
2 major pathways of soil feedback
Direct- via root herbivores, pathogens, symbionts
Indirect- through effect of soil decomposer subsystem on supply of nutrients
What was the arbuscular mycorrhizal fungi experiment by Grime et al?
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
What was the Van der Heijden et al experiment?
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
Root pathogen experiment by Van der Putten et al.
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
Invasiveness of plant species experiment by Klironomos
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)
How can you break the cycle of pathogen accumulation?
Crop rotation
Bardgett et al plant nutrient cycling experiment
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
Northup et al plant nutrient cycling experiment
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
Bowman et al plant nutrient cycling experiment
How slow-growing herbs and fast-growing grass coexist in alpine meadows
Herb increases soil microbial activity, less N available
