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

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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?

* primer isn’t a complete review of Ch 11

learning objectives
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 …
classification a means to make sense of the diversity
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.)
slide4

Taxonomic groups:

Phylogenic Tree of Life

  • Prokaryotes
  • Bacteria
  • Archaea
  • Eukaryotes
  • Protists
  • Fungi
  • Plants
  • Animals

(Pace 1997)

important groups of soil organisms

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)

a cup of soil contains
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

relative sizes
Relative Sizes

Animated gif –

view in slideshow mode

Note ruler for scale

http://commtechlab.msu.edu/sites/dlc-me/zoo/zdrr0101.html

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

Soil bacteria

Soil fungi

slide10
Aggregates held together by:

Fungal hyphae

Bacterial “glues”

Organic matter

Microflora –

hyphae

clay

sand

silt

bacteria

fungi

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.

bacteria

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
fungi vs bacteria

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

microfauna
Microfauna

Amoebae

Ciliate

  • heterotrophs; some parasitic
  • feed on bacteria and fungi
  • release plant nutrients – protozoa KEY for N

Flagellate

Nematode

Nematode

eeee!

slide15

Microfauna –

Nematodes(non-segmented, round worms)

  • Widely distributed in forest soils
  • Saprophytic and parasitic groups
  • Some predatory species attack tree roots and cause damage
slide16

Microfauna –

Protozoa

  • Most abundant of all soil fauna
  • One-celled
  • Feed on bacteria
  • Up to 30% of all mineralized N from protozoa
mesofauna
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
macrofauna
Macrofauna
  • heterotrophs
  • shred plant material
  • feed on bacteria and fungi associated with organic matter

Photo by Suzanne Paisley

earthworms

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
earthworm casts vs soil

Macrofauna –

Earthworm casts vs. soil

38.8

1.11

849

13.8

From text Table 11.6

dung beetles

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

influence of soil biota on soil processes

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

recall rate of decomposition depends on

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

slide25

Ecosystem Function –

See also text Fig 11.1

Soil Food Web

some generalizations

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)