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Soil Biology – A Primer * Who is who & What do they do? PowerPoint Presentation
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Soil Biology – A Primer * Who is who & What do they do?

Soil Biology – A Primer * Who is who & What do they do?

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Soil Biology – A Primer * Who is who & What do they do?

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  1. Soil Biology – A Primer* Who is who & What do they do? * primer isn’t a complete review of Ch 11

  2. Learning Objectives • List the major groups of soil organisms … • Identify the roles of organisms • Draw a simplified soil food web ... • Describe the conditions affecting growth… • Discuss the beneficial functions …

  3. Classification – A means to make sense of the diversity • Taxonomic groups (plants, animals, bacteria, fungi, protista) • Functional groups & size (microflora vs. macroflora/fauna) – Table 11.1 • Carbon/energy source (detritivores vs. fungivores; autotrophic vs. heterotrophic) – Fig 11.1, Table 11.3 • Environmental tolerance (thermophiles, anaerobes, etc.)

  4. Taxonomic groups: Phylogenic Tree of Life • Prokaryotes • Bacteria • Archaea • Eukaryotes • Protists • Fungi • Plants • Animals (Pace 1997)

  5. Taxonomic groups: Biological Kingdoms

  6. Size, functional groups: Important Groups of Soil Organisms Vascular plants, mosses (autotrophs) • Macroflora • Microflora • Macrofauna Vascular plants (root hairs), algae, actinomycetes, bacteria, and fungi (auto- and heterotrophs) Vertebrates, arthropods, earthworms, snails… (herbivores, detritivores, predators) • Mesofauna • Microfauna Arthropods, worms (detritivores, predators) Nematodes, protazoa… (detritivores, fungivores, bacterivores, predators)

  7. A cup of soil contains... Size: Bacteria Fungi Protozoa Nematodes Arthropods Earthworms 200 billion { See text Table 11.1 Microflora, or “microbes” 100,000 meters 20 million { Microfauna 100,000 50,000 { Macro- and mesofauna <1 Immobile organisms all primarily found in the rhizosphere, the zone of soil closest to plant roots

  8. Relative Sizes Animated gif – view in slideshow mode Note ruler for scale http://commtechlab.msu.edu/sites/dlc-me/zoo/zdrr0101.html

  9. Microflora • heterotrophs (bacteria, fungi) & autotrophs (algae, cyanobacteria) • the primary decomposers • release plant available nutrients • stabilize soil aggregates Soil bacteria Soil fungi

  10. Aggregates held together by: Fungal hyphae Bacterial “glues” Organic matter Microflora – hyphae clay sand silt bacteria

  11. Microflora – Fungi • The major agent of decay in acid environs • Network of hyphae: improves soil structure • Decomposition of cellulose!!! • Can compete with higher plants for N N.B. – Fungi are in their own separate kingdom from plants: they are non-photosynthetic, and their RNA is actually more like animals, than like plants.

  12. Microflora – Bacteria • Exist in both forest and grassland soils • Aerobic, anaerobic, and facultative forms • Autotrophic and heterotrophic forms • Most do best under high Ca2+, high pH • Do best when soil temp 20-40C (68-100F) but seldom killed by temperature extremes

  13. Microflora – Fungi vs. bacteria Single-celled, can form colonies Tube-like body; hyphae Aerobic, anaerobic, and facultative species Aerobic only Rapid regeneration time (hours); can respond quickly to nutrient additions Generally slower growth rate

  14. Microfauna Amoebae Ciliate • heterotrophs; some parasitic • feed on bacteria and fungi • release plant nutrients – protozoa KEY for N Flagellate Nematode Nematode eeee!

  15. Microfauna – Nematodes(non-segmented, round worms) • Widely distributed in forest soils • Saprophytic and parasitic groups • Some predatory species attack tree roots and cause damage

  16. Microfauna – Protozoa • Most abundant of all soil fauna • One-celled • Feed on bacteria • Up to 30% of all mineralized N from protozoa

  17. Mesofauna Collembola (springtails) Fungus feeding mite Nematode feeding mite • heterotrophs (detritivores, predators) • feed on fungi, protozoa, nematodes, mites • important in regulating populations of everything smaller

  18. Macrofauna • heterotrophs • shred plant material • feed on bacteria and fungi associated with organic matter Photo by Suzanne Paisley

  19. Macrofauna – Earthworms • Probably the most important component of soil fauna (not in acid soils, not in very dry soils) • Pass as much as 30 tons/ha of soil through their bodies each year • Excreted casts higher in N, P, K, Ca, Mg, pH, & CEC • Promote good soil structure and aeration

  20. Macrofauna – Earthworm casts vs. soil 38.8 1.11 849 13.8 From text Table 11.6

  21. Macrofauna – Dung Beetles • Key disposer of elephant dung • and so a protected species! (you can imagine the ‘or else’…) Amboseli National Park, Kenya Tembe Elephant ReserveKwaZulu Natal, South Africa Addo National Park, South Africa

  22. – Mendenhall

  23. Ecosystem Function – Influence of soil biota on soil processes Break up O.M., mineralize and immobilize nutrients Bind aggregates, hyphae entangle particles Regulate bacterial and fungal populations Indirectly affect structure Regulate above pops.; fragment plant tissue Fecal pellets, pores Mix O.M. and mineral soil; pores; feces Fragment plant tissue

  24. Ecosystem Function – Recall: Rate of decomposition depends on – • Physical and chemical nature of the litter material • Temperature and moisture of the soil environment • Aeration (vs. anaerobic) • The kinds and numbers of soil fauna  More bugs, and more different kinds of bugs, means more decomposition

  25. Ecosystem Function – See also text Fig 11.1 Soil Food Web

  26. Ecosystem geography – Some generalizations . . . • Forested soils more biologically diverse • Forested soils dominated by fungi • Faunal biomass (and activity) greater per ha in grasslands • Cultivated soils least diverse, less biomass, fewer organisms cf. text Table 11.4 (p. 453)