Transcript Soil Chemistry (continued)

Soil Biology – A Primer*
Who is who
&
What do they do?
* primer isn’t a complete review of Ch 11
Learning Objectives
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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
• 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.)
Taxonomic groups:
Phylogenic Tree of Life
Prokaryotes
• Bacteria
• Archaea
Eukaryotes
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Protists
Fungi
Plants
Animals
(Pace 1997)
Taxonomic groups:
Biological Kingdoms
Size, functional groups:
Important Groups of Soil Organisms
• Macroflora
Vascular plants, mosses (autotrophs)
• Microflora
Vascular plants (root hairs), algae,
actinomycetes, bacteria, and fungi
(auto- and heterotrophs)
• Macrofauna
Vertebrates, arthropods, earthworms,
snails…
(herbivores, detritivores, predators)
• Mesofauna
Arthropods, worms (detritivores,
predators)
• Microfauna
Nematodes, protazoa… (detritivores,
fungivores, bacterivores, predators)
Size:
A cup of soil contains...
Microflora,
or “microbes”
Microfauna
Macro- and
mesofauna
Bacteria 200 billion
{ Fungi
100,000 meters
See text
Table 11.1
Protozoa 20 million
{ Nematodes 100,000
Arthropods
{ Earthworms
50,000
<1
Immobile organisms all primarily found in the rhizosphere,
the zone of soil closest to plant roots
Relative Sizes
Animated gif –
view in slideshow mode
Note ruler for scale
http://commtechlab.msu.edu/sites/dlc-me/zoo/zdrr0101.html
Microflora
• heterotrophs (bacteria, fungi) & autotrophs (algae,
cyanobacteria)
• the primary decomposers
• release plant available nutrients
• stabilize soil aggregates
Soil bacteria
Soil fungi
Microflora –
hyphae
clay
Aggregates held
together by:
sand
– Fungal hyphae
– Bacterial “glues”
– Organic matter
silt
bacteria
Microflora –
Fungi
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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 nonphotosynthetic, and their RNA is actually more like animals, than like plants.
Microflora –
Bacteria
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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
Microflora –
Fungi vs. bacteria
Fungi
Bacteria
Tube-like body;
hyphae
Single-celled, can form
colonies
Aerobic only
Aerobic, anaerobic, and
facultative species
Generally slower
growth rate
Rapid regeneration
time (hours); can
respond quickly to
nutrient additions
Microfauna
• heterotrophs; some parasitic
• feed on bacteria and fungi
Ciliate
Flagellate
• release plant nutrients –
protozoa KEY for N
Amoebae
Nematode
Nematode
eeee!
Microfauna –
Nematodes (non-segmented, round worms)
– Widely distributed in forest soils
– Saprophytic and parasitic groups
– Some predatory species attack tree roots and
cause damage
Microfauna –
Protozoa
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Most abundant of all soil fauna
One-celled
Feed on bacteria
Up to 30% of all mineralized N from protozoa
Mesofauna
• heterotrophs (detritivores, predators)
• feed on fungi, protozoa, nematodes, mites
• important in regulating populations of everything smaller
Fungus feeding mite
Nematode feeding mite
Collembola (springtails)
Macrofauna
• heterotrophs
• shred plant material
• feed on bacteria and
fungi associated with
organic matter
Photo by Suzanne Paisley
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
Macrofauna –
Earthworm casts vs. soil
Characteristic
Earthworm casts
Soils
silt & clay (%)
38.8
22.2
Bulk density (g/cm3)
1.11
Structural stability
849
CEC (cmolc/kg)
From text Table 11.6
13.8
1.28
65
3.5
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 Reserve
KwaZulu Natal, South Africa
Addo National Park, South Africa
– Mendenhall
Ecosystem Function –
Influence of soil biota on soil processes
Nutrient cycling
Soil structure
Microflora
Break up O.M., mineralize
and immobilize nutrients
Bind aggregates,
hyphae entangle
particles
Microfauna
Regulate bacterial and
fungal populations
Indirectly affect
structure
Mesofauna
Regulate above pops.;
fragment plant tissue
Fecal pellets, pores
Macrofauna
Fragment plant tissue
Mix O.M. and mineral
soil; pores; feces
Ecosystem Function –
Recall: Rate of decomposition depends on –
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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 –
Soil Food Web
See also text Fig 11.1
Ecosystem geography –
Some generalizations . . .
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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)