Chapter 7Decomposers and Decomposition

Decomposition?

DecompositionDecompositionbreakdown of chemical bonds formed during the construction of plant and animal tissue.Organisms that feed on dead organic matter or detritus Microbial decomposersbacteria and fungiDetritivoresanimals that feed on dead material

Carbon Carbon sequestrationCO2 vs. organic matterForests vs. barren landAtmosphere vs. biomass

Stages of decompositionLeachingloss of soluble sugars/dissolved compoundsFragmentationreduction into smaller particles physical/chemical fragmentation

Energy processingEnergy and nutrients from organic compoundsoxidation of carbohydratesrespiration

Mineralizationorganic inorganic

Immobilizationinorganic organic

DecomposersGroups based on sizeMicrofloramost common decomposersbacteriaanimal materialfungiplant materialAerobicrespirationAnaerobicfacultative/obligate anaerobesFermentationsugars organic acids/alcohol

DecomposersMicrofauna/microflora

Food QualityEnergy and nutrient sourceLitterdead plant materialQuality related to chemical bonds/structuresimple sugars vs. complex carbohydratesLignincomplex class of carbohydrateslittle net gain of energy for decomposers

Rate of decompositionInverse relationship between rate and lignin contentQuality influences feeding of large detritivores

Aquatic environmentsPhytoplanktonlow lignin contentVascular plantshigh lignin content

O2 dependentLow O2 absence of fungi

Animal matterChemical breakdown easier than plantsFlesh consumed by scavengers70% decomposed by bacteria and arthropods (maggots)Temperature dependent

Fecal matterMostly decomposedHerbivorespartially digested organic matterSpecialized detririvores larvae incubate and feedTumblebugsincubate larvae

Physical influenceTemperature and moistureInfluence rate of decompositionDecomposition highest in warm/wet climatesTemperature parallels CO2 release

NutrientsNitrogen nutrient valueOrganisms require N for growth during mineralizationMineralization and immobilization taking place simultaneouslyNet mineralization rate

Stages of nutrient concentrationWater soluble compounds leachedDependent upon soil moistureN increasesimmobilization from other sourcesAs C quality declines net release of NDependent upon original nutrient content

Aquatic decompositionSimilar to terrestrial ecosystemsInfluenced by abundance of waterMore stable environment favors decompositionMore accessibility to detritivores

Aquatic systemsParticulate organic matter (POM)Coarse particulate organic matter (CPOM)Fine particulate organic matter (FPOM)Water depth determines organic makeupBenthic organic matter bacteriaAerobic vs. anaerobicDissolved organic matter (DOM)

Aquatic sourcesDOM readily available Sourcesalgae, zooplanktonDeath of phyto/zooplanktonBacteria concentrate DOMMineralization and immobilization of nutrientsExcretion of exudates and feces

Organic matter processingPhysical mechanismWater soaked leaves sink5 30% organic matter leached

Biological mechanismCovered with bacteria & fungiCPOM & FPOMDegrade cellulose and metabolize lignin

Shredders attack CPOMFeed also on attached microbesBecomes FPOMFilterers / collectors gather FPOMFeed also on attached microbesGrazers feed on algal coatingsleftovers enter stream as FPOMGougers feed on woody debrisPredators feed on all the above Flowing water

Nutrient passes from water column plants consumer another consumer poop = nutrient cyclingDownstream flow = new dimension Physical retentionStorage in wood detritusLeaf sedimentsBeds of macrophytesBiological retentionUptake and storage in plant/animal tissue

Recycling, retention & downstream displacementDownstream transport + nutrient cycling = nutrient spiralingOne cycle = Uptake of an atom from DOMPassage through food chainReturn to water for reuseSpiraling = distance of one cycleshorter cycle = tighter spirallonger cycle = more open spiral

River Continuum ConceptFrom headwaters to mouth continuum of changes in conditions

Headwater streams (1-3) Swift, cold, forestedStrongly heterotrophicDominant organismsShredders CPOMCollectors FPOM

Midorder streams (4-6) Riparian vegetation importantCanopy opens primary productionTemperature increases / current slowsPrimary production > community respirationDominant organismsCollectors FPOMGrazers algae & macrophytes

Higher order streams (6 10) Channel wider & deeperVolume of flow increasesAutotrophic production decreasesShift back to heterotrophyEnergy from FPOMUtilized by bottom dwellersPhytoplankton & zooplankton population minimal