The Life in Our Soil - Transform Compost Systems · 2016-02-19 · The Life in Our Soil An...
Transcript of The Life in Our Soil - Transform Compost Systems · 2016-02-19 · The Life in Our Soil An...
The Life in Our Soil An Introduction to Soil
Microbiology
Slides Prepared by: Richard Stehouwer Department of Crop & Soil Sciences
Adapted and presented by John Paul, PhD with permission
Function of soil
• Anchor plant roots • Supply water to plant roots • Provide air for plant roots • Furnish nutrients for plant growth • Release water with low levels of nutrients
Soil Components The 4 parts of soil
MineralMatter45%
SoilWater25%
SoilAir
25%
OrganicMatter
5%
About ½ of the soil volume is
solid particles
About ½ of the soil volume is pore space
Why should you care
about soil organic matter
(SOM)?
SOM Improves Soil Physical Properties
– Increased granulation and aggregate stability
– Makes heavy soils easier to work
– Increases water infiltration rates
– Increases water holding capacity
– Decreases erosion
If your soil looks like this…
You can avoid this!
Soil aggregates held together by: – Fungal hyphae
– Bacterial “glues”
– Organic matter
sand
silt
hyphae clay
bacteria
SOM Improves Soil Chemical Properties
– Increases Cation Exchange Capacity so the soil is better able to store and supply plant nutrients
– Increases pH buffering so the soil resists changes in pH
– Reduces Aluminum, Iron, and Manganese toxicity in acidic soil
Why should you care
about soil organic
matter (SOM)?
• SOM Improves Soil Biological Properties – Greater abundance, diversity and activity of soil microbes
– Increased nutrient cycling
– Increased root elongation and abundance
– Increased access to water and nutrients
Why should you care about soil organic
matter (SOM)?
What is Soil Organic
Matter?
• All material in soil that contains (reduced) carbon.
• SOM is derived from – Plant residue (both litter
and roots)
– Animal remains and excreta
– Living soil microbes (microbial biomass)
• Over time microbes transform fresh organic material into stable soil organic matter
Crop residue
Bacteria
Fungi Actinomycetes
SOM
Diversity of soil organisms
Soil organisms can be grouped on the basis of: – Size: how big they are
– Species: who they are related to
– Function: how they make their living
Size of Soil Organisms
Meso or mid-size
(2–0.2 mm)
Micro or small
(<0.2mm)
Earthworm
Alfalfa root
Mite
Bacteria
Yeast
Springtail
Macro or large
(>2 mm)
Species and function • Animals
– Vertebrates: gophers, mice, voles, snakes
– Arthropods: spiders, ants, beetles, maggots
– Annelids: earthworms
– Mollusks: snails, slugs
– Nematodes Parasitic nematodes in insect larvae
Mouth parts of bacteria-feeding nematode
Water bear
Predatory nematode
Species and function
Plants, the primary producers
– Vascular plants: roots of all crop and vegetable plants
– Algae
Algae
Legume roots with nitrogen fixing nodules
The rhizosphere
Plant Root
• The zone of soil that is significantly influenced by living roots
• Usually extends about 2mm out from the root surface
• The rhizosphere is enriched in organic material due to root exudates and sloughed off root cells.
• Microbial activity in the rhizosphere may be 2 – 10 greater than in the bulk soil.
Species and function
Fungi
AM fungus
Slime mold
Mushroom
Protists
Flagellate Ciliate
Amoeba
Red yeast
Numbers of Species
In a healthy soil one might find… Several species of vertebrate animals Several species of earthworms 20-30 species of mites 50-100 species of insects Dozens of species of nematodes Hundreds of species of fungi Thousands of species of bacteria and
actinomycetes
Abundance of soil organisms
Number Biomass1
Organism per gram soil (lbs per (~1 tsp) acre 6”) Earthworms – 100 – 1,500 Mites 1-10 5 – 150 Nematodes 10 – 100 10 – 150 Protozoa up to 100 thousand 20 – 200 Algae up to 100 thousand 10 – 500 Fungi up to 1 million 1,000 – 15,000 Actinomycetes up to 100 million 400 – 5,000 Bacteria up to 1 billion 400 – 5,000
1 Biomass is the weight of living organisms
• Ecosystem Stability. Soil has several ways to accomplish the same function (system redundancy)
• Ecosystem Resilience. Soil has the ability to bounce back from a severe disturbance
Benefits of diversity
• Organic matter decomposition
• Symbiotic Nitrogen Fixation
• Mycorrhizal Fungi
Beneficial microbe-plant-soil
interactions Some examples
Organic matter decomposition Everyone is involved
• Earthworms – Mix fresh organic materials
into the soil
– Brings organic matter into contact with soil microorganisms
Corn leaf pulled into nightcrawler burrow
Millepede
Ants
• Soil insects and other arthropods
– Shred fresh organic material into much smaller particles
– Allows soil microbes to access all parts of the organic residue
Organic matter decomposition Everyone is involved
• Bacteria – Population increases
rapidly when organic matter is added to soil
– Quickly degrade simple compounds - sugars, proteins, amino acids
– Have a harder time degrading cellulose, lignin, starch
– Cannot get at easily degradable molecules that are protected
Bacteria on fungal strands
Spiral bacteria
Rod bacteria
Organic matter decomposition Everyone is involved
• Fungi – Grow more slowly and
efficiently than bacteria when organic matter is added to soil
– Able to degrade complex organic molecules such as cellulose, lignin, starch
– Give other soil microorganisms access to simpler molecules that were protected by cellulose or lignin
Soil fungus
Fungus on poplar leaf
Tree trunk rotted by fungi
Fairy ring
Organic matter decomposition Everyone is involved
• Actinomycetes – The cleanup crew
– Become dominant in the final stages of decomposition
– Attack the highly complex and decay resistant compounds
• Cellulose
• Chitin (insect shells)
• Lignin
Organic matter decomposition Everyone is involved
• Protists and nematodes, the predators – Feed on the primary
decomposers (bacteria, fungi, actinomycetes)
– Release nutrients (nitrogen) contained in the bodies of the primary decomposers
Amoeba
Bacteria-feeding nematode
Predatory nematode Rotifer
Organic matter decomposition Carbon and Nitrogen Cycling
During each cycle of degradation about 2/3 of the organic carbon is used for energy and released as carbon dioxide (CO2)
Bacteria, Fungi Soil organic matter Nematodes, protists, humus
CO2
CO2
Plant litter
During each cycle of degradation about 1/3 of the organic carbon is used to build microbial cells or becomes part of the soil organic matter
Organic matter decomposition Carbon and Nitrogen Ratio
Average C/N ratio of bacteria and
fungi is 8:1
Litter C/N ratio
around 24:1
CO2
C/N ratio 8:1
2/3 of carbon released as CO2
Microbial C/N ratio is maintained at 8:1 with no uptake or release of N
Organic matter decomposition Carbon and Nitrogen Ratios
2/3 of carbon released as CO2
Average C/N ratio of bacteria and
fungi is 8:1
Litter C/N ratio
around 90:1
CO2
C/N ratio 30:1
Immobilization
Soil N
Microbial C/N ratio is maintained at 8:1 by taking up N from soil
Organic matter decomposition Carbon and Nitrogen Ratios
Average C/N ratio of bacteria and
fungi is 8:1
Litter C/N ratio
around 9:1
CO2
C/N ratio 3:1
2/3 of carbon released as CO2
Mineralization Soil N
Microbial C/N ratio is maintained at 8:1 by releasing N to the soil
Symbiotic Nitrogen Fixation
• Many bacteria have the ability to “fix” or convert atmospheric nitrogen into forms that plants can utilize.
• Some of these bacteria, notably the rhizobia species, form symbiotic relationships with legumenous plants – The plant provide Rhizobia
with a steady source of food (sugars)
– The rhizobia provides the plant with nitrate nitrogen
– Efficiency nitrogen fixation is greatly increased by this relationship
Rhizobia bacteria
Rhizobia nodules on bean roots
Effect of rhizobia inoculation on soybean
Inoculated Not inoculated
Mycorrhizal fungi Plant/fungi symbiosis
• Mycorrhizae means “fungus root” • Fungi live in close association with plant roots
• May live on the external surface of roots (ectomycorrhizal)
• Fungal hyphae may invade root cells (endomycorrhizal)
VAM fungi growing in symbiotic association with a plant root.
Root cells
Fungal hyphae
Vesicles – food storage
Arbuscule – exchanges nutrients with plant
Mycorrhizal fungi Plant/fungi symbiosis
With mycorrhizal fungi
Growth of Douglas Fir seedlings
No mycorrhizal fungi
• Plants supply fungi with sugars (energy) • Fungal hyphae grow 5 – 10 cm beyond plant roots
• Extend to soil pores too large for root hairs • Increase plant nutrient supply, especially
phosphorus • Increase plant water supply
Mycorrhizal fungi Soil structure benefit
Mycorrhizal fungi present • Soil structure stabilized and
strengthened • Structure is maintained when
immersed in water
Mycorrhizal fungi absent • Soil structure is weak • Structure is not maintained
when immersed in water
Soil factors that affect
microorganism growth
• Organic matter
• Aeration (oxygen)
• Moisture and temperature
• Soil fertility and pH
Effects of soil management
practices on soil organisms Forest
Crop Monoculture
Grassland
Crop rotation
Effects of soil management
practices on soil organisms
Maintaining high soil organic matter levels and residue cover on the soil surface (no till systems) tends to increase microbial diversity and activity
Pesticide applications have variable effects on
microbial populations
The black box is open
• A healthy soil ecosystem is extremely diverse and complex
– Large numbers of organisms
– Many different kinds organisms
– Many different functions
• A diverse soil ecosystem is stabile and resilient
•Soil organisms have developed many complex interdependencies that benefit agricultural soil functions.
•Soil management activities can significantly affect the life in your soil.
Photo Credits
Pedatory nematode: Kathy Merifield, Oregon State Univ.
Bacterial and root feeding nematode: Elaine Ingham, Oregon State Univ.
Nematode: Mark Blaxter, Univ. Edinburgh
Earthworms: Clive Edwards, Ohio State Univ.
Fungi on poplar: Bryce Kendrick
Mycorrhizae and soil aggregation: Ted St.John, USDA-ARS
Amoeba: Ohio State Univ. – Lima
Water bear: Kamamusi
Ciliate: BioMedia Products
Bear in water: Katami Nat’l Park, Alaska
Rotifer: Nikon Microscopy, Inc.
Fairy ring: Univ. Tenn.
Millipede, mite, springtail: Penn State Univ. Insect Fair
Disking: Colorado State Univ.
Strip Crop: Ingolf Vogler
No till corn: Mich. State Univ.
Rangeland: North Dakota St. Univ.
Rhizobia: Frank Dazzo, Mich. State Univ.
Actinomycetes: Paul R. August, Univ. Minn.
Soybean growth: RIAL Siebersdorf
Rod bacteria: Univ. Georgia
Thanks to: Dr. Mary Ann Bruns, Soil Microbial Ecologist, Penn State Univ.
for reviewing this presentation and for providing some of the photographs