What is the significance of soil organisms?

• Affect nutrient availability and cycling

– Recycle carbon and plant nutrients

– Capture of atmospheric nitrogen (nitrogen fixation)

– Take part in oxidation‐reduction reactions

– Aid plants in nutrient uptake

• Produce compounds that stabilize soil structure

• Cause plant and animal diseases

Name 4 soil organism titles

• Primary producers convert solar energy into carbohydrates

– Vascular plants, algae, lichens, photosynthetic bacteria

• Primary consumers feed on primary producers

– Herbivores and detritivores

• Secondary consumers feed on primary consumers

– Bacteria, fungi, actinomycetes, carnivores

• Tertiary consumers feed on secondary consumers

– Carnivores

Use C in combined organic compounds

Heterotrophs

Source of energy = biochemical oxidation

– All animals, fungi, actinomycetes, most bacteria

Chemoheterotrophs

Source of energy = solar radiation

– A few algae

Photoheterotrophs

Fix C from CO₂

Autotrophs

Source of energy = biochemical oxidation

– Ammonia oxidizers (Nitrosomonas)

– Sulfur oxidizers (Thiobacillus denitrificans)

Chemoautotrophs

Source of energy = solar radiation

– Higher plants

– Algae and cyanobacteria

» Chorella

» Nostoc

Photoautotrophs

What so burrowing animals do?

– Moles, prairie dogs, etc.

– Consume

• Vegetation

• Other soil animals

– Functions

• Aerate soil

• Move and mix soil materials

• Produce macro‐channels

– Are often considered

detrimental in agricultural and

residential soils

What do Earthworms do for soil?

– Consume: plant material

– Functions

• Important in nutrient cycling

– Ingest nutrients and deposit them in casts

– Mix organic materials from higher layers into lower layers

• Important for soil structure

– Worm channels increase aeration and infiltration

– Casts, high in polysaccharides,  bind soil particles

– Soil conditions

• Earthworms prefer high Ca, neutral soils

What are Arthropods and what do they do?

– Mites, ants, termites,

millipedes, etc.

– Feed:  on plant residue

– Impact:  

• Break down organic matter

• Mix soil materials

• Increase soil porosity

What are Gastropods?

– slugs and snails

• herbivores, detritus

feeders, carnivores,

scavengers, parasites

Name 2 kinds of Nematodes

• Predaceous

– Prey on other soil microorganisms

» Nematodes, fungi, bacteria, algae,

protozoa, insect larvae

• Parasitic

– Infest plant roots

– Very widespread

– Predispose plants to microbial diseases

» Effects of root‐knot nematodes are shown

in photo at left

Name  some soil microfauna

nematode. protoazoa

What are Protozoa?

– Mobile, single‐celled organisms

– Most varied and numerous of soil microfauna

– Amoebas, ciliates, flagellates

– Feeding: bacteria

– Conditions

• Moist, well‐drained soils

• Surface horizons

Typically roots occupy approximately ____ of soil volume

1%

_______ may comprise 30‐50% of plant mass

Roots

What do roots do?

Plants are primary producers and add organic C through their roots

– Roots release organic substances into the soil

• This creates the rhizosphere

– A microbial “cafeteria” with increased numbers and diversity of species

– May have altered soil chemical properties

– Roots are not photosynthetic, but they respire

•Consume O2     • Produce CO2

– Roots create channels as they push through the soil

– Roots consume nutrients and change soil conditions

Soil region immediately surrounding plant roots?

(Usually about 2 mm from the root surface)

Rhizosphere

Zone of relatively high microbiological activity

rhizosphere

Rhizosphere microbes can interact with ______ _______

plant roots

pH and nutrient availability are different from that of

the bulk soil in the ____________________.

rhizosphere

What is soil algae and what does it do?

Chlorophyll‐containing organisms

– Capable of carrying out photosynthesis

– Require light (photoautotrophs)

• Several hundred species are found in soil

• Effects:  

– Add organic matter to soils

– Some form microbiotic crusts with other microorganisms

• Need a fairly moist environment

What are fungi and what do they do?

Yeasts, molds, mushrooms

• Single celled to multi‐celled organisms

– Cannot photosynthesize (chemotrophs)

– Live on fixed (organic) carbon (heterotrophs)

– Some are predatory

• Function: Fungi are very important for breaking down

organic materials in soils

– Especially complex woody materials

• Effects:

– Important in plant nutrition

– Cause many plant diseases

– Can cause human diseases

___________ are capable of breaking down 

cellulose and lignin

Fungi 

What is Mycorrhizae?

– the association (usually symbiotic) of fungi with the roots of seed plants

• fungal hyphae can grow 5 to 15 cm from plant root

• fungus contributes to nutrient uptake (especially P)

• plant provides sugars and a home

• improves drought tolerance

• protects plants from pathogens

• can be parasitic

– 90% of the world’s plants are mycorrhizal

Uptake of phosphorus and other immobile nutrients is enhanced by _________ which extend the reach of the root system.

mycorrizae

Types of Mycorrhizae?

• Endomycorrhizae

– Also called Vesicular‐Arbuscular mycorhizae (VAM)

– Arbuscules develop withinplant cells

– No root or outside structural changes

– In nearly all cultivated plants

(some trees and shrubs)

• Ectomycorrhizae

– Hyphae form compact mantle or sheath over root surface

– Hyphae penetrate between cells of root cortex

– In temperate trees and shrubs