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

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Presentation on theme: "Soil Biology – A Primer* Who is who & What do they do? * primer isn’t a complete review of Ch 11."— Presentation transcript:

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

5 Biological Kingdoms Taxonomic groups:

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

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

8 Relative Sizes Animated gif – view in slideshow mode Note ruler for scale

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

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

11 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. Microflora –

12 Bacteria Exist in both forest and grassland soils Aerobic, anaerobic, and facultative forms Autotrophic and heterotrophic forms Most do best under high Ca 2+, high pH Do best when soil temp 20-40C (68-100F) but seldom killed by temperature extremes Microflora –

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

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

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

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

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

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

19 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 Macrofauna –

20 Earthworm casts vs. soil CharacteristicEarthworm castsSoils silt & clay (%)22.2 Bulk density (g/cm 3 ) 1.28 Structural stability65 CEC (cmol c /kg) 3.5 From text Table Macrofauna –

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

22 – Mendenhall

23 Influence of soil biota on soil processes Nutrient cyclingSoil structure Microflora Microfauna Mesofauna Macrofauna 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 Fragment plant tissue Mix O.M. and mineral soil; pores; feces Ecosystem Function –

24 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 Ecosystem Function –

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

26 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) Ecosystem geography –


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