2 Introduction - Soil Organisms Reading Assignment: Brady and Weil, Chapter 103 lecturesIt’s AliveBeneath the SurfaceSoil EngineersBlended learning materials available on web site and DVD
3 Learning Objectives Lecture 1 – Its Alive Define key terms pertaining to soil organismsSurvey of organism typesIdentify soil organisms’ activities within Food WebLecture 2 – Beneath the SurfaceDescribe 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 microorganismsLecture 3 – Soil EngineersExplain why earthworms, ants and termites are called soil engineersDiscuss how people can manage soil to encourage a healthy, diverse soil community.
4 Lecture 1 TopicsSurvey of Soil OrganismsFood Web
5 Lecture 2 Topics Microorganisms living beneath the surface Symbiotic RelationshipsNitrogen Fixation
6 Lecture 3 TopicsEarthwormsAnts and TermitesSoil Management
8 Learning Objectives Lecture 1 – Its Alive Define key terms pertaining to soil organismsSurvey of organism typesIdentify soil organisms’ activities within Food Web
9 Lecture 1 – TopicsSurvey of soil organismsFood WebVocabulary
10 Do you remember?How is organic matter important to the healthy functioning of soil?Stabilization of soil aggregatesImproved water holding capacityReservoir of plant nutrients and cation exchange capacityNow you’ll learn….Soil Organisms are the principle players in the dynamic processes that control organic matter turnover
11 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.
12 How many soil organisms per gram of soil? Bacteria – 1 billion/gActinomycetes million/gFungi – million/gProtozoa – 1 million/gNematodes – 50/g
13 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 diatomsMicrobes <0.1 mmFungi (Eukaryotes)Bacteria and Archaea (Prokaryotes)
15 Survey: Soil Microbes Soil bacteria Bacteria on fungi Fungi decomposing leaf tissueMycorrhizal bodies and hyphaeEctomycorrhizaeVesiclesImages from NRCS:
16 Survey: Soil Flora and Microfauna Plant root, Fig 10.10Diatoms,Root feeding nematodeProtozoa: amoeba eating bacteriaImages from NRCS:
17 Survey: Mesofauna and Macrofauna ShreddersFungal feeder – orabatid mitePredatorsHerbivoreImages from NRCS:
18 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.
19 Metabolic Grouping – C and Energy Source of EnergySource of CarbonBiochemical OxidationSolar RadiationCombined organic carbonChemoheterotrophs: All animals, plant roots, fungi, actinomycetes, and most other bacteriaExamples:EarthwormsAspergillus sp.Azotobacter sp.Pseudomonas sp.Photoheterophs: Just a few algaeCarbon dioxideChemoautotrophs: Many archea and bacteriaAmmonia oxidizers – Nitrosomonas sp.Sulfur oxidizers – Thiobacillus denitrificansPhotoautotrophs: Plant shoots, algae, and cyanbacteriaChorella sp.Nostoc sp.
20 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 plantsanimalsHerbivores – living plants (parasitic nematodes, insect larvae, rodents, termites, ants, beetle larvae)Detritivores – dead plantsPredators – animalsFungivores – fungiBacterivores – bacteriaParasites - live off of but do not consume other organisms.fungibacterialive off of but do not consume other organisms.
21 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.
22 Measures of Diversity Species diversity – Functional diversity – Functional redundancy –organisms present are evenly distributed among a large number of speciesthe 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 processSpecies diversity – organisms present are evenly distributed among a large number of speciesFunctional 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 processStability – 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.
23 Diversity by LocationForested areas – more diverse soil fauna and more fungal-dominated microfloraGrasslands – Total fauna mass per hectare and level of activity higher than in forestCultivated Fields – lower levels in numbers and biomass of soil organisms than native grasslands due to loss caused by tillage.
24 Soil Food Web Primary Producers By-products CO2 Primary Consumers Solar EnergyPlants, algae, lichens, bacteriaPrimary ProducersPrimary ConsumersSecondary ConsumersHigh Level ConsumersBy-productsPlants debris (detritus)CO2Saprophytic bacteria, actinomycetesMites & other shreddersEarthworm shreddersSaprophytic fungiNematodes (root feeders)Mycorrhizal fungiHeat Energy LossFeces and dead bodiesMineral NutrientsBacteria, fungi & actinomycetesMitesSpringtailsEarthwormsProtozoaNematodes (root feeders)HumusAmoebasEarthwormsPredatory mitesBeetle, spider, centipede, ant predatorsNematodesMammal and bird predators
25 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 fungiThe activity of organisms is more important than the identity. Functional diversity vs. species diversity.
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