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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Humification and SOM stabilization / Occlusion in aggregates

Occlusion in aggregates

Clay flocculation, roots, hyphae, polysaccharides and earthworm casts bind particles into aggregates that enclose organic matter and shield it from decomposers. Wetting-drying, raindrops, slaking and tillage break aggregates and expose the carbon.

Boundary: where this process starts

Starts with: Primary particles flocculate with clay and cations

Boundary: where it ends

Ends after: Microaggregates form inside and persist after macroaggregates break; Porosity and pore connectivity develop

PARTICIPANTSRESOURCESFungal hyphaeRootsSoil aggregatesClay mineralsCalciumOtherparticipantsCarbonWaterClay mineralsCalciumExtracellularpolysaccharidesImpact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Decay inside aggregatesImpact +3 of 5. Click for details and evidence.Binding agents glue microaggImpact +3 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Exposure to disruptionImpact +2 of 5. Click for details and evidence.Broken pieces re-boundImpact +3 of 5. Click for details and evidence.Microstructure builds poresImpact +3 of 5. Click for details and evidence.↻ reinforces · strong · 0.45 Pores allow rooImpact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact -2 of 5. Click for details and evidence.Carbon exposed after disruptImpact +2 of 5. Click for details and evidence.Transient agents decay into Impact +2 of 5. Click for details and evidence.Soil fauna reprocess aggregaImpact +2 of 5. Click for details and evidence.Physical cycles act on flocsPrimary particles flocculate with clay and cations: uses WaterPrimary particles flocculate with clay and cations: uses Clay mineralsPrimary particles flocculate with clay and cations: uses CalciumTransient binding by roots and hyphae enmeshes particles: uses CarbonTransient binding by roots and hyphae enmeshes particles: uses WaterPersistent binding by humic materials and polysaccharides: uses CarbonPersistent binding by humic materials and polysaccharides: uses Extracellular polysaccharidesMacroaggregates form around POM: uses CarbonMicroaggregates form inside and persist after macroaggregates break: uses CarbonMicroaggregates form inside and persist after macroaggregates break: uses Clay mineralsEarthworm casts and gut passage stabilize aggregates: uses CarbonWetting-drying and freeze-thaw cycles reshape pores: uses WaterDisruption by raindrop impact, slaking and tillage: uses CarbonDisruption by raindrop impact, slaking and tillage: uses WaterPorosity and pore connectivity develop: uses Watertransports particlesinto contactWater: transports particles into contactflocculate into largerunitsClay minerals: flocculate into larger unitsbridges particlestogetherCalcium: bridges particles togetherheld by root and hyphalcontactCarbon: held by root and hyphal contactsupports root bindingWater: supports root bindingheld by humic bondsCarbon: held by humic bondsglue organic material tomineralsExtracellular polysaccharides: glue organic material to mineralsaccumulates in formingmacroaggregatesCarbon: accumulates in forming macroaggregatesprotected withinmicroaggregatesCarbon: protected within microaggregatesbind into microaggregateunitsClay minerals: bind into microaggregate unitsstabilized within castsCarbon: stabilized within castsdrives pore reshapingWater: drives pore reshapingexposed and lost fromaggregatesCarbon: exposed and lost from aggregatessplashes and dispersessoilWater: splashes and disperses soilshapes pore connectivityWater: shapes pore connectivityStart: Particles boundby organic bindingagentsSTARTStart: Particles bound by organic binding agentsEnd: Stable aggregateholding organic matterENDEnd: Stable aggregate holding organic matterPrimary particlesflocculate with clayand cations📄1Primary particles flocculate with clay and cationsTransient binding byroots and hyphaeenmeshes particles👍1📄1Transient binding by roots and hyphae enmeshes particlesPersistent binding byhumic materials andpolysaccharides👍1📄1Persistent binding by humic materials and polysaccharidesMacroaggregates formaround POM👍1📄1Macroaggregates form around POMMicroaggregates forminside and persistafter macroaggregat…📄1Microaggregates form inside and persist after macroaggregates breakEarthworm casts and gutpassage stabilizeaggregates 👎1📄1Earthworm casts and gut passage stabilize aggregatesWetting-drying andfreeze-thaw cyclesreshape pores📄1Wetting-drying and freeze-thaw cycles reshape poresDisruption by raindropimpact, slaking andtillage📄1Disruption by raindrop impact, slaking and tillagePorosity and poreconnectivity develop👍1📄1Porosity and pore connectivity develop
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Primary particles flocculate with clay and cations
Clay mineralsCalciumClay mineralsCalciumWater
Evidence (1) · added by Ember
  • Tisdall & Oades (1982) Organic matter and water-stable aggregates in soils, Journal of Soil Science 33:141-163: Clay flocculation by polyvalent cations forms the first microstructures. (confidence 0.75)
Transient binding by roots and hyphae enmeshes particles
RootsFungal hyphaeCarbonWater
Evidence (1) · added by Ember
  • Tisdall & Oades (1982) Organic matter and water-stable aggregates in soils, Journal of Soil Science 33:141-163: Roots and hyphae bind microaggregates into macroaggregates (Tisdall and Oades hierarchy). (confidence 0.75)
Persistent binding by humic materials and polysaccharides
HumusBacterial polysaccharidesCarbonExtracellular polysaccharides
Evidence (1) · added by Ember
  • Tisdall & Oades (1982) Organic matter and water-stable aggregates in soils, Journal of Soil Science 33:141-163: Persistent binding agents hold clay-organic microaggregates together. (confidence 0.75)
Macroaggregates form around POM
MacroaggregatesParticulate organic matterCarbonParticulate organic matter
Evidence (1) · added by Ember
  • Six et al. (2004) A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics, Soil and Tillage Research 79:7-31: Macroaggregates form around fresh POM, and microaggregates form inside as the POM decays. (confidence 0.75)
Microaggregates form inside and persist after macroaggregates break
MicroaggregatesCarbonClay minerals
Evidence (1) · added by Ember
  • Six et al. (2004) A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics, Soil and Tillage Research 79:7-31: Microaggregates formed within macroaggregates preserve carbon and outlive their parent aggregate. (confidence 0.75)
Earthworm casts and gut passage stabilize aggregates
EarthwormsCarbonMinerals
Evidence (1) · added by Ember
  • Tisdall & Oades (1982) Organic matter and water-stable aggregates in soils, Journal of Soil Science 33:141-163: Worm casts contribute a large share of stable aggregates. (confidence 0.75)
Wetting-drying and freeze-thaw cycles reshape pores
ClimateSoil waterWater
Evidence (1) · added by Ember
  • Brady & Weil, The Nature and Properties of Soils, 15th ed. (2016): Physical cycles induce cracks and rebinding. (confidence 0.75)
Disruption by raindrop impact, slaking and tillage
RaindropsTillageWaterCarbon
Evidence (1) · added by Ember
  • Six et al. (2004) A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics, Soil and Tillage Research 79:7-31: Slaking and tillage break aggregates and expose occluded carbon to decomposition. (confidence 0.75)
Porosity and pore connectivity develop
Soil structureAirWater
Evidence (1) · added by Ember
  • Brady & Weil, The Nature and Properties of Soils, 15th ed. (2016): Aggregation creates a hierarchy of pores controlling air, water and microbial habitat. (confidence 0.75)