EcologyEcologyLecture 5Lecture 5

Ralph KirbyRalph Kirby

What is DecompositionWhat is Decomposition

Decomposition is the breakdown of the chemical Decomposition is the breakdown of the chemical structure of living organisms that occurs on structure of living organisms that occurs on death of those organismsdeath of those organismsIt involves the release of the energy stored in It involves the release of the energy stored in those compounds as part of autotrophic growththose compounds as part of autotrophic growthReleases the chemicals that form part of the Releases the chemicals that form part of the organic matter ultimately as inorganic chemicalsorganic matter ultimately as inorganic chemicalsEssential for life on Earth because without it, all Essential for life on Earth because without it, all carbon would be trapped as dead organic matter carbon would be trapped as dead organic matter and there would be no recyclingand there would be no recycling

Decomposition is made up of many processesDecomposition is made up of many processes– IngestionIngestion– ExcretionExcretion– Chemical decompositionChemical decomposition– LeachingLeaching– Physical structure changesPhysical structure changes

All heterotrophs need to be decomposers to All heterotrophs need to be decomposers to come extent in order to obtain nutrientscome extent in order to obtain nutrientsHowever, more usual to consider decomposers However, more usual to consider decomposers to be those that feed on dead organic matter as to be those that feed on dead organic matter as their major source of energy and carbontheir major source of energy and carbon– Microbial DecomposersMicrobial Decomposers

Bacteria, Fungi, etcBacteria, Fungi, etc– DetritivoresDetritivores

AnimalsAnimals

Stages of decompositionStages of decompositionLeachingLeaching– Loss of soluble compoundsLoss of soluble compounds

Occurs in a cycle with fragmentation and is abioticOccurs in a cycle with fragmentation and is abiotic

FragmentationFragmentation– Reduction of organic matter into smaller particles either physically or Reduction of organic matter into smaller particles either physically or

chemicallychemicallyBoth biotic and abioticBoth biotic and abioticBoth biotic microbial and none microbial fragmentation involves some uptake Both biotic microbial and none microbial fragmentation involves some uptake by the decomposer for respiration etcby the decomposer for respiration etc

MineralizationMineralization– This is the release of various end products that are none organic in This is the release of various end products that are none organic in

naturenatureCarbon dioxideCarbon dioxideWaterWaterNitrateNitrateAmmoniaAmmoniaSulphateSulphate

ImmobilizationImmobilization– Incorporation of part of the decomposed matter into the decomposers Incorporation of part of the decomposed matter into the decomposers

own organic formown organic form

Very large number of different Very large number of different organisms are involved in organisms are involved in decompositiondecomposition– BacteriaBacteria

AerobicAerobic– Most efficientMost efficient

soilsoil

AnaerobicAnaerobic– Less efficientLess efficient

Termite gutTermite gutUngulate gutUngulate gutAquatic sedimentAquatic sediment

– FungiFungiCellulose degradingCellulose degrading

– CellulasesCellulases

Lignin degrading\Lignin degrading\– LigninasesLigninases

– MicrofaunaMicrofaunanematodesnematodes

– MicrofloraMicrofloraProtozoa and algaeProtozoa and algae

– MesofaunaMesofaunaMites and springtailsMites and springtails

– MacrofaunaMacrofaunaMillipedes and termitesMillipedes and termites

– MegafaunaMegafaunaEarthworms and snailsEarthworms and snails

Note the presence of a food Note the presence of a food chainchain– Large insects feed on smaller Large insects feed on smaller

insects feed on fungi and insects feed on fungi and bacteriabacteria

Dead organic matter provides Dead organic matter provides both energy and nutrientsboth energy and nutrientsHowever, dead organic matter However, dead organic matter is made up of a wide variety of is made up of a wide variety of different chemicaldifferent chemicalThese chemicals have different These chemicals have different stabilities during decompositionstabilities during decomposition– Sugar, amino acids etc are Sugar, amino acids etc are

valuable and utilized firstvaluable and utilized first– Proteins, lipid and less Proteins, lipid and less

complex polysaccharides like complex polysaccharides like starch are easy to break down starch are easy to break down and utilized nextand utilized next

– Next, the complex hard to Next, the complex hard to break down polysaccharides break down polysaccharides like celluloselike cellulose

– Finally, the complex materials Finally, the complex materials like lignin are utilizedlike lignin are utilized

– The order is based on the The order is based on the energy needed to complete the energy needed to complete the breakdown and uptake of the breakdown and uptake of the material material

Complex Organic Molecules in Complex Organic Molecules in DetritisDetritis

ProteinsProteins– Amino bonds easily broken by proteasesAmino bonds easily broken by proteases

Starch, glycogen and similar polysaccharidesStarch, glycogen and similar polysaccharides– Storage material and easily broken down by various enzymesStorage material and easily broken down by various enzymes

LipidsLipids– Cell membrane and storage material. Lipases break this down with Cell membrane and storage material. Lipases break this down with

varying efficienciesvarying efficiencies

HemicelluloseHemicellulose– Plant cell wall material, most easily broken down part.Plant cell wall material, most easily broken down part.

CelluloseCellulose– Structural material. Cyrstaline and can be difficult to breakdown. Variety Structural material. Cyrstaline and can be difficult to breakdown. Variety

of cellulases and other enzymes neededof cellulases and other enzymes needed

LigninLignin– Very complex random structured moleculesVery complex random structured molecules– Requires specialised enzymes for breakdown utilizing free radicalsRequires specialised enzymes for breakdown utilizing free radicals– Lignin peroxidases, polyphenol oxidases and laccasesLignin peroxidases, polyphenol oxidases and laccases

Note effect of lignin Note effect of lignin contentcontentUsually stated that Usually stated that fungi are the major fungi are the major lignin degraderslignin degradersNot absolutely trueNot absolutely trueMany bacteria Many bacteria produce lignin produce lignin degrading enzymes degrading enzymes like polyphenol like polyphenol oxidases and lignin oxidases and lignin peroxidases peroxidases particularly the particularly the ActinomycetesActinomycetesThermophilic Thermophilic degradation of degradation of organic matter rich in organic matter rich in cellulose and lignin cellulose and lignin particularly involves particularly involves thermophilic thermophilic Actinomycetes – Actinomycetes – CompostingComposting

Note anaerobic Note anaerobic decomposition of decomposition of plants in water plants in water environmentenvironment– Anaerobic bacteria Anaerobic bacteria

involvedinvolved

Also affect large Also affect large faunafauna– Termites like cellulose Termites like cellulose

and ligninand lignin– Earthworms do not Earthworms do not

like ligninlike lignin

Decomposition of animal material is much Decomposition of animal material is much quicker than plant material especially at high quicker than plant material especially at high temperaturestemperaturesBacteria are very important and enzymes Bacteria are very important and enzymes needed are less specialisedneeded are less specialisedSome insects such as blowflies involvedSome insects such as blowflies involvedSuccession of insects (and also bacteria) allow Succession of insects (and also bacteria) allow estimation of time of death in murder casesestimation of time of death in murder casesAlso allows season when death occurred to be Also allows season when death occurred to be identified as well as if the body has been movedidentified as well as if the body has been movedSmall animal body will be reduced to bone and Small animal body will be reduced to bone and hair (30% of original mass) in 7-10 days during hair (30% of original mass) in 7-10 days during summersummerAt lower temperatures, mummification can occur At lower temperatures, mummification can occur followed by fragmentation and scatteringfollowed by fragmentation and scattering

Fecal matter is also important due to the various fauna involved Fecal matter is also important due to the various fauna involved in decompositionin decomposition

However, it is already high degraded, but provides a rich However, it is already high degraded, but provides a rich sources of nutrient to specialised detritivoressources of nutrient to specialised detritivores

Examples are dungbeetlesExamples are dungbeetles– Lay their eggs in a made dung pat and develop through Lay their eggs in a made dung pat and develop through

larvae and pupae in itlarvae and pupae in it

Decomposition is affected by Decomposition is affected by the physical environmentthe physical environmentWaterWater– Moisture needed by bacteria Moisture needed by bacteria

and fungi for optimal and fungi for optimal decompositiondecomposition

– But not soakedBut not soaked

TemperatureTemperature– Microbial ActivityMicrobial Activity

New HampshireNew Hampshire– 7.2oC7.2oC– 621mm evaporation621mm evaporation

West VirginiaWest Virginia– 12.2oC12.2oC– 720mm evaporation720mm evaporation

VirginiaVirginia– 14.4oC14.4oC– 806mm evaporation806mm evaporation

Carbon dioxide release versus day temperatureCarbon dioxide release versus day temperature

Decomposers Decomposers need to get need to get something for their something for their effortsefforts– CarbonCarbon– NitrogenNitrogen– Other mineralsOther minerals

Balance between Balance between immobilization and immobilization and mineralizationmineralization

Note initial Note initial leaching and lossleaching and loss

Litterbag studiesLitterbag studiesNot Ideal however, because they do not involve soilNot Ideal however, because they do not involve soil

Litterbag studies Litterbag studies are not idealare not idealSee net See net accumulation of accumulation of immobilized immobilized nitrogen from nitrogen from outside the bag outside the bag when there is a when there is a high initial nitrogen high initial nitrogen level to excourage level to excourage initial microbial initial microbial decompositiondecomposition– LeachingLeaching– IncreaseIncrease

Good carbon Good carbon sourcessources

– DecreaseDecreasePoor carbon Poor carbon sourcessources

Note importance of all macro and micronutrients in Note importance of all macro and micronutrients in decomposition, not just carbon and nitrogendecomposition, not just carbon and nitrogen– SulphurSulphur– CalciumCalcium– ManganeseManganese– PhosphorusPhosphorus– etcetc

All are cycledAll are cycled

Overall pattern for Overall pattern for aquatic environment is aquatic environment is the same as terrestrial the same as terrestrial environmentenvironmentMore stable physical More stable physical environment for faunaenvironment for fauna– ShreddersShredders– CollectorsCollectors– GrazersGrazers– ScrapersScrapers

Particulate organic Particulate organic matter to bottommatter to bottom– Anaerobic bacteriaAnaerobic bacteria

Note presence of algae Note presence of algae etc increasing organic etc increasing organic matter toomatter tooCiliates and zooplankton Ciliates and zooplankton eat bacteriaeat bacteria