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We generally think of soil from the ground up

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. However, there is a parallel universe below us.

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We generally think of soil from the ground up

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  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. 2002 Ecol. Econom. 41

  5. Architecture & Biology of soil Iain M Young

  6. 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 10-6 m2 c. 107 bacteria  4 x 10-6 m2 c. 5 km fungi  1 x 10-4 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. FEED-FORWARD BIOTICACTIVITY SOILARCHITECTURE FEED-BACK SELF-ORGANISATION OF THE SOIL SYSTEM “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 Pores full of water Pores emptying Pores empty CO2 will move 1cm in 1 day in this system. 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. R.solani Sterile Volumetric moisture content (%) Root surfactant Matric potential (- cm) Impact of biota on moisture release curve

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

  18. Fine-scale porosity measurements Zero day Unplanted Outer planted Inner planted 5.29 4.64 7.55 11.67 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 N2 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 • 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 2000. 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

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