1. We generally think of soil from the ground up
Soil as a medium for plant growth
We eat plants or eat things that eat plants
We need soil to eat

2. However, there is a parallel universe below us
The health and functioning of this universe is critical to the functioning of the world we see at the soil surface

3. Functioning of soil biota underground
Is critical for the ability of soils to support plant life
This soil- biota- plant- predator continuum is integral to ecosystem functioning
Life underground is also the most poorly understood component of this continuum

4. Value of ecosystem services
value ($trillion)
soil 50
clean water 6
food etc. 2
genetic resources 2
Total ($60T) is about twice global GNP
Single most valuable ecosystem
Boumans et al Ecol. Econom. 41

5. Architecture & Biology
of soil
Iain M Young

6. ~It is the habitat of all soil biota
Q] What is the structure of soil?
Key characteristics:
~ It is the framework in and
through which ALL soil process
occur.
~ It exists in three dimensions.
~ It’s heterogeneous in space
and time.
~It is the habitat of all soil biota

7. Life in
Inner Space

8. The soil-plant-microbe interface:
There literally can be billions of individual
organisms in a relatively small area.
1g of soil = c. 20m2
In 1 g of soil we have:
c. 10,000 protozoa  7 x m2
c. 107 bacteria  4 x m2
c. 5 km fungi  1 x m2
5.5 x 10-4% of the total space
is covered

9. World underground is likely as heterogeneous as the world at the surface
With similar population density

10. Soil as a microbe sees it

11. ‘Inner Space’.

12. Naked amoebae
accessing small
pores - shape
changing
20 mm

13. Fungal hyphae
Bridging soil
Pores,
Rhizotonia solani
seeking roots

14. SELF-ORGANISATION OF THE SOIL SYSTEM
FEED-FORWARD
FEED-BACK
BIOTIC ACTIVITY
SOIL ARCHITECTURE
“We can no more manufacture soil with a tank of chemicals than we can invent a rain forest or create a single bird”
Worster 1993

15. Soil water and microbes
CO2 will move 1cm
in 1 day in this
system.
Pores full
of water
Pores
emptying
Pores
empty
CO2 will move 1cm
in less than 1 hour
in this system.
Complexity of pore-scale structure allows air and water can coexist in soil – a vital fact for sustaining life
The relative proportion determines most key rate processes in soil
Only a tiny fraction of the soil pore
space will contain active microbes.

16. Impact of biota on moisture release curve
Matric potential (- cm)
Volumetric moisture content (%)
R.solani
Sterile
Root
surfactant

17. Field-scale interactions between soil water
and soil microbes

18. Fine-scale porosity measurements
Zero day Unplanted Outer planted Inner planted
Inner planted: Greater geostatistical range:
~ larger porosities
~ aggregate (non-random) structures:
correlation length increases in presence
of biota.
Simulation model:
Origin & Loss of fractal scaling:
Crawford, Verral & Young (1998)

19. Soil microbes live to eat
Energy from organic substrates is primary source of food
Aerobic and anaerobic reactions
Can also get energy from chemical reactions
Look at N cycle

20. Nitrogen basics In atmosphere N2 gas (77% of atmosphere)
N is the most limiting plant nutrient
N can also be a primary contaminant in water systems

21. The N cycle

22. How does it go from atmosphere to soil?
Lightning N NO3
Bacterial associations

23. All transformations of N in soil are microbially mediated
Eating is the first step
This is what happens when microbes eat SOM, they need N to use the C
Mineral N to organic N
Immobilization
Organic N to NH4+ or NO3 -
Mineralization

24. Energy, respiration reactions
NH4 + to NO3 - - nitrosimonas, nitrobacter
Nitrification
NO3- to gaseous N
Denitrification
Occurs in anaerobic environments
Wetlands, soil microsites

25. Soil water and microbial processes
Nitrogen transformations are dependent significantly
on the soil’s ability to hold water and allow gaseous transport
Young & Ritz Soil & Till. Res.

26. For Nitrogen transformations
All are microbially mediated
Which occur depend on local environmental conditions
Local environmental conditions are also somewhat dependent on microbial populations

27. In general: If you want your soil to work for you
High microbial population is required for highly functional soil
Food source- primarily organic matter- is requirement for high microbial population
Microbes are ubiquitous- no need to seed, just feed