Soil BiologySoil Biology

Who is down Who is down there and what there and what do they dodo they do

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 …

Sun

Humus

Producers

ConsumersDecomposers

air water

soil

Important Groups of Soil OrganismsImportant Groups of Soil Organisms

• MacrofloraMacroflora

• MicrofloraMicroflora

• MacrofaunaMacrofauna

Vascular plantsVascular plants, mosses, mosses

Vascular plantsVascular plants, algae, actinomycetes, , algae, actinomycetes, bacteria, and fungi**bacteria, and fungi**

Vertebrates, arthropods, earthworms, Vertebrates, arthropods, earthworms, snails… snails…

** Fungi are actually their own ** Fungi are actually their own separate kingdomseparate kingdom

• MesofaunaMesofauna

• MicrofaunaMicrofauna

Bigger arthropods, wormsBigger arthropods, worms

Nematodes, protazoaNematodes, protazoa

Size/type classSize/type class e.g. and functional group/energy acquisitione.g. and functional group/energy acquisition

Soil Animals – micro, meso, macro

BacteriaMicroflora

Microflora

Nematodes

Protozoa

Microfauna

20-200 kg/ha!20-200 kg/ha!

Mites

Springtails

Mesofauna

Other invertebrates

Mesofauna

Worms

Voles!

Macrofauna

A cup of soil containsA cup of soil contains......

BacteriaBacteria

Fungi*Fungi*

ProtozoaProtozoa

NematodesNematodes

ArthropodsArthropods

EarthwormsEarthworms

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microfaunamicrofauna

macro- and macro- and mesofaunamesofauna

200 billion200 billion

100,000 meters

20 million20 million

100,000100,000

50,00050,000<1<1

Microflora, Microflora, or “microbes”or “microbes”

* Fungi are * Fungi are actually their actually their own separate own separate kingdomkingdom

B – BacteriaA – ActinomycetesMy – MycorrhizaeH – Saprophitic fungusN – NematodeCP – Ciliate protozoaFP – Flagellate protozoaM – Mite

< 1mm

1/10 mm

• Gain energy from nematodesGain energy from nematodes• 3 groups, yeast, mold, mushrooms3 groups, yeast, mold, mushrooms• symbiotic relationships with symbiotic relationships with mostmost

plantsplants• Produce chemicals that are toxicProduce chemicals that are toxic

• The major agent of decay in The major agent of decay in acid environsacid environs• Network of Network of hyphaehyphae: : improves soil structureimproves soil structure• Decomposition of Decomposition of cellulosecellulose!!!!!!• Can Can compete with higher plantscompete with higher plants for N for N

Fungi Fungi – tens of thousands of species– tens of thousands of species

Sun

Humus

Producers

ConsumersDecomposers

Aggregates held together by:

1. Fungal hyphae2. Bacterial “glues”3. Organic matter

sand

silt

hyphaeclay

bacteria

Bacteria – 1 billion -1 trillion/g soil (up to 20,000 spp.)

• Exist in both forest and grassland soils• Most do best under high Ca2+, high pH• Do best when soil temp 20-40C (68-100F)

but seldom killed by temp extremes

Sun

Humus

Producers

ConsumersDecomposers

Fungi vs. bacteriaFungi vs. bacteriaFungiFungi BacteriaBacteria

Tube-like body; hyphae

Generally slower growth rate

Single-celled, can form colonies

Rapid regeneration time (hours); can respond quickly to nutrient additions

Complex, mutually beneficial Complex, mutually beneficial relationshipsrelationships

fungi

bacteria

Amoebae

CiliateFlagellate

• some parasitic• feed on bacteria

and fungi• release plant nutrients –

protozoa KEY for N

Nematode

MicrofaunaMicrofauna

Sun

Humus

Producers

ConsumersDecomposers

MicrofaunaMicrofauna

– Widely distributed in forest soils– Saprophytic and parasitic groups– Some predatory species attack

tree roots and cause damage

• Nematodes (non-segmented, round worms)

sap·ro·phyte An organism, that grows on and derives its nourishment from dead or decaying organic matter.

MicrofaunaMicrofauna

– Most abundant of all soil Most abundant of all soil faunafauna– One-celledOne-celled– Feed on bacteriaFeed on bacteria– Up to 30% of all mineralized N from protozoaUp to 30% of all mineralized N from protozoa

• ProtozoaProtozoa

Collembola (springtails)

Fungus feeding mite

• heterotrophs (detritivores, predators)heterotrophs (detritivores, predators)• feed on fungi, protozoa, nematodes, mitesfeed on fungi, protozoa, nematodes, mites• important in regulating populations of everything important in regulating populations of everything smallersmaller

Nematode feeding mite

MesofaunaMesofauna

Photo by Suzanne Paisley

• shred plant materialshred plant material• feed on bacteria feed on bacteria and fungi associated and fungi associated with organic matterwith organic matter

MacrofaunaMacrofauna

Earthworm middenEarthworm midden

Earthworms Earthworms – (have gizzards!)– (have gizzards!)

• Probably the most important component of Probably the most important component of soil fauna (not in acid soils, not in very dry soil fauna (not in acid soils, not in very dry soils)soils)

• Eat OM & pass as much as 30 tons/ha of Eat OM & pass as much as 30 tons/ha of soil through their bodies (mixing horizons) soil through their bodies (mixing horizons) each yeareach year

• Promote good soil structure and aerationPromote good soil structure and aerationest. wt. of worms in U.S. = 10X wt. of entire human population

Great for fishing! Worm farming - Huge industry!

Sun

Humus

Producers

ConsumersDecomposers

air water

soil

Some generalizations . . .Some generalizations . . .• Forested soils more biologically diverseForested soils more biologically diverse• Forested soils dominated by fungiForested soils dominated by fungi• Faunal biomass (and activity) greater per ha in Faunal biomass (and activity) greater per ha in

grasslandsgrasslands• Cultivated soils least diverse, less biomass, Cultivated soils least diverse, less biomass,

fewer organismsfewer organisms