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Ecosystem Energetics: Soil Food Web & Biotic Regulation

Explore the intricate web of interactions in healthy soils, from organic compounds to complex food chains, with a focus on energy flow and nutrient cycling. Learn how soil biota impact plant health and soil structure. Aldo Leopold's insight underscores the vital role of land beyond mere soil.

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Ecosystem Energetics: Soil Food Web & Biotic Regulation

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  1. Soil Food Web and “Biotic Regulation” “Land, then, is not merely soil; it is a foundation of energy flowing through a circuit of soils, plants and animals”. Aldo Leopold

  2. Organic portion composed of: 5% 10% 85% Humus & decomposing organic litter

  3. “organic” • What is special about Organic compounds? They have ENERGY • Food chain passes energy along through photosynthesis and respiration

  4. Green plants can directly use sun Photosynthesis: CO2 + H2O + solar energy C6H12O6 + O2 organic !

  5. Rest of us are only indirectly solar-powered Respiration: C6H12O6 + O2 ENERGY + CO2 + H2O

  6. Fourth-order consumer Tertiary consumer heterotrophs Secondary consumer Primary consumer Primary Producer green plants; photosynthetic bacteria and algae autotrophs

  7. Food Chain Concept Energy is passed from one trophic level to the next.

  8. Healthy soil function depends on interactions of many organisms Mite eating a springtail

  9. A Complex Soil Food Webin an old growth Douglas fir forest Complexity refers to number of species & kinds of species Higher complexity means more energy transfer

  10. Complexity of the Soil Food Web in Several Ecosystems

  11. Soil food web complexity is desirable. Why? 1. What do plants do for soil? What does soil do for plants? 2. Nutrient cycling is more rapid in complex systems 3. More competition for organisms that cause disease 4. Biota can retain and “hold” nutrients 5. Improves “tilth” structure = aggregate stability provided by glues, worm burrows, castings increases ability to hold water, allow drainage, move nutrients, let roots in

  12. Typical Numbers of Soil Organisms in Healthy Ecosystems

  13. Biomass of Soil Organisms in Four Ecosystems

  14. Where are soil biota? • Litter: fungi important here • Most are in top several inches (A horizon) • Rhizosphere • Humus : fungi • surfaces of soil aggregates (blocks, crumbs, plates, etc) • Pore spaces

  15. rhizosphere 1/10 inch Exudates: carbohydrates and proteins secreted by roots attracts bacteria, fungi, nematodes, protozoa Bacteria and fungi are like little fertilizer bags Nematodes and protozoa eat bacteria & fungi and excrete the fertilizer

  16. Rhizosphere Where roots and soil meet Cells, proteins, sugars released by young root tip

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