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Fundamentals of Soil Science
Soil Organisms
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Introduction - Soil Organisms
Reading Assignment: Brady and Weil, Chapter 10 3 lectures It’s Alive Beneath the Surface Soil Engineers Blended learning materials available on web site and DVD
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Learning Objectives Lecture 1 – Its Alive
Define key terms pertaining to soil organisms Survey of organism types Identify soil organisms’ activities within Food Web Lecture 2 – Beneath the Surface Describe how a community of microorganisms assimilates plant and animal materials, creating soil organic matter, recycling carbon and mineral nutrients, and supporting plant growth. Relate soil quality to microorganisms Lecture 3 – Soil Engineers Explain why earthworms, ants and termites are called soil engineers Discuss how people can manage soil to encourage a healthy, diverse soil community.
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Lecture 1 Topics Survey of Soil Organisms Food Web
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Lecture 2 Topics Microorganisms living beneath the surface
Symbiotic Relationships Nitrogen Fixation
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Lecture 3 Topics Earthworms Ants and Termites Soil Management
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Lecture 1 It’s Alive
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Learning Objectives Lecture 1 – Its Alive
Define key terms pertaining to soil organisms Survey of organism types Identify soil organisms’ activities within Food Web
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Lecture 1 – Topics Survey of soil organisms Food Web Vocabulary
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Do you remember? How is organic matter important to the healthy functioning of soil? Stabilization of soil aggregates Improved water holding capacity Reservoir of plant nutrients and cation exchange capacity Now you’ll learn….Soil Organisms are the principle players in the dynamic processes that control organic matter turnover
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Why is the soil alive? A handful of healthy soil likely contains billions of organisms. A diversity of unseen creatures interact in the soil – they are microorganisms.
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How many soil organisms per gram of soil?
Bacteria – 1 billion/g Actinomycetes million/g Fungi – million/g Protozoa – 1 million/g Nematodes – 50/g
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What are the creatures in the soil?
Fauna (animals) Macrofauna >2 mm (moles, prairie dogs, earthworms, millipedes) Mesofauna mm (tiny springtails and mites) Microfauna <0.1 mm (nematodes and single-celled protozoans) Flora (plants) Roots of plants as well as microscopic algae and diatoms Microbes <0.1 mm Fungi (Eukaryotes) Bacteria and Archaea (Prokaryotes)
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Relative Size
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Survey: Soil Microbes Soil bacteria Bacteria on fungi
Fungi decomposing leaf tissue Mycorrhizal bodies and hyphae Ectomycorrhizae Vesicles Images from NRCS:
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Survey: Soil Flora and Microfauna
Plant root, Fig 10.10 Diatoms, Root feeding nematode Protozoa: amoeba eating bacteria Images from NRCS:
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Survey: Mesofauna and Macrofauna
Shredders Fungal feeder – orabatid mite Predators Herbivore Images from NRCS:
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Satisfying Carbon Needs
Soil Organism classification: Heterotrophs – rely on organic compounds for carbon and most also for energy. Autotrophs – obtain carbon from carbon dioxide and energy from photosynthesis or oxidation of various elements. Heterotrophs are far more numerous in soil, but some of the autotrophs perform fundamental soil processes including ammonium oxidation to nitrite.
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Metabolic Grouping – C and Energy
Source of Energy Source of Carbon Biochemical Oxidation Solar Radiation Combined organic carbon Chemoheterotrophs: All animals, plant roots, fungi, actinomycetes, and most other bacteria Examples: Earthworms Aspergillus sp. Azotobacter sp. Pseudomonas sp. Photoheterophs: Just a few algae Carbon dioxide Chemoautotrophs: Many archea and bacteria Ammonia oxidizers – Nitrosomonas sp. Sulfur oxidizers – Thiobacillus denitrificans Photoautotrophs: Plant shoots, algae, and cyanbacteria Chorella sp. Nostoc sp.
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Who eats what? Soil organisms can be grouped by what they eat:
Herbivores – Detritivores – Predators – Fungivores – Bacterivores – Parasites – Living plants (parasitic nematodes, insect larvae, rodents, termites, ants, beetle larvae) dead plants animals Herbivores – living plants (parasitic nematodes, insect larvae, rodents, termites, ants, beetle larvae) Detritivores – dead plants Predators – animals Fungivores – fungi Bacterivores – bacteria Parasites - live off of but do not consume other organisms. fungi bacteria live off of but do not consume other organisms.
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What are Organisms Doing?
Soil is an ecosystem. Many scientists believe that there are more species in existence below the surface of the Earth than above it. A balance among these organisms make possible the functions of a healthy, high quality soil.
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Measures of Diversity Species diversity – Functional diversity –
Functional redundancy – organisms present are evenly distributed among a large number of species the capacity to use a variety of substrates and carry out an array of processes. presence of several organisms to carry out each enzymatic or physical process Species diversity – organisms present are evenly distributed among a large number of species Functional diversity – the capacity to use a variety of substrates and carry out an array of processes. Functional redundancy – presence of several organisms to carry out each enzymatic or physical process Stability – ability of soil to perform functions such as cycling of nutrients, assimilation of wastes, in the face of a wide variety of environmental conditions. Resilience – ability of soil to “bounce back” to health after a severe disturbance. Keystone species – their population may indicate health of entire soil ecosystem.
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Diversity by Location Forested areas – more diverse soil fauna and more fungal-dominated microflora Grasslands – Total fauna mass per hectare and level of activity higher than in forest Cultivated Fields – lower levels in numbers and biomass of soil organisms than native grasslands due to loss caused by tillage.
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Soil Food Web Primary Producers By-products CO2 Primary Consumers
Solar Energy Plants, algae, lichens, bacteria Primary Producers Primary Consumers Secondary Consumers High Level Consumers By-products Plants debris (detritus) CO2 Saprophytic bacteria, actinomycetes Mites & other shredders Earthworm shredders Saprophytic fungi Nematodes (root feeders) Mycorrhizal fungi Heat Energy Loss Feces and dead bodies Mineral Nutrients Bacteria, fungi & actinomycetes Mites Springtails Earthworms Protozoa Nematodes (root feeders) Humus Amoebas Earthworms Predatory mites Beetle, spider, centipede, ant predators Nematodes Mammal and bird predators
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Summary Soil is a complex, diverse ecosystem
Organisms incorporate plant residues into soil, return CO2 to the atm where it can be re-fixed into plants. In the process, soil organic matter is formed and essential plant nutrients are released. 80-90% of metabolic activity in soil food web is bacteria and fungi The activity of organisms is more important than the identity. Functional diversity vs. species diversity.
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