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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Humification and SOM stabilization / Mineral-associated organic matter (MAOM) formation

Mineral-associated organic matter (MAOM) formation

Dissolved organic matter and microbial products reach mineral surfaces and bind by ligand exchange, cation bridging or weak adsorption, forming layered organo-mineral complexes. Binding capacity is limited by clay and iron oxide content and can be reversed by desorption or microbial mining.

Boundary: where this process starts

Starts with: Dissolved organic matter and microbial products reach mineral surfaces

Boundary: where it ends

Ends after: Mineral association protects from enzymes and microbes; Clay and iron content set storage capacity

PARTICIPANTSRESOURCESMineralsurfacesDissolvedorganic matterClay mineralsMicrobialproductsIron oxidesOtherparticipantsCarbonIron oxidesDissolvedorganic carbonCalciumClay mineralsImpact +3 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.40%Impact +3 of 5. Click for details and evidence.30%Impact +2 of 5. Click for details and evidence.30%Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +1 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Capacity depends on mineraloImpact -2 of 5. Click for details and evidence.↻ balances · weak · 0.2 Exchange with solutiImpact +2 of 5. Click for details and evidence.Returned carbon re-enters soImpact +4 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.Impact +2 of 5. Click for details and evidence.Protection depends on capaciImpact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Dissolved organic matter and microbial products reach mineral surfaces: uses Dissolved organic carbonBinding mechanism: uses CarbonBinding mechanism: uses Iron oxidesBinding mechanism: uses CalciumLigand exchange with iron and aluminium oxides: uses CarbonPolyvalent cation bridging with calcium and clay: uses CarbonPolyvalent cation bridging with calcium and clay: uses CalciumWeak hydrophobic and van der Waals adsorption: uses CarbonLayered organo-mineral structure builds up: uses CarbonMineral association protects from enzymes and microbes: uses CarbonClay and iron content set storage capacity: uses Iron oxidesClay and iron content set storage capacity: uses Clay mineralsDesorption or microbial mining returns some carbon to solution: makes CarbonmakesMineral surface area, reactive metals and the saturation of mineral-associated carbon: uses CarbonMineral surface area, reactive metals and the saturation of mineral-associated carbon: uses Iron oxidesMineral surface area, reactive metals and the saturation of mineral-associated carbon: uses Dissolved organic carbonMineral surface area, reactive metals and the saturation of mineral-associated carbon: uses Clay mineralsadsorbs onto mineralsurfacesDissolved organic carbon: adsorbs onto mineral surfacesbound to mineralsurfacesCarbon: bound to mineral surfacesprovide ligand bindingsitesIron oxides: provide ligand binding sitesbridges to negativechargesCalcium: bridges to negative chargesbound through ligandexchangeCarbon: bound through ligand exchangelinked to clay surfacesCarbon: linked to clay surfacesbridges organic matterto clayCalcium: bridges organic matter to clayweakly held on mineralsCarbon: weakly held on mineralsstacked into layeredassociationsCarbon: stacked into layered associationsshielded from enzymesand microbesCarbon: shielded from enzymes and microbesadd extra sorptioncapacityIron oxides: add extra sorption capacityset total bindingcapacityClay minerals: set total binding capacityreleased back intosolutionCarbon: released back into solutionsaturated on mineralsurfacesCarbon: saturated on mineral surfacesreactive metals bindcarbonIron oxides: reactive metals bind carbonsorbed onto mineralsurfacesDissolved organic carbon: sorbed onto mineral surfacesprovide surface area forbindingClay minerals: provide surface area for bindingStart: Solublecompounds meet mineralsurfaceSTARTStart: Soluble compounds meet mineral surfaceEnd: Organo-mineralcomplex formedENDEnd: Organo-mineral complex formedDissolved organicmatter and microbialproducts reach miner…📄1Dissolved organic matter and microbial products reach mineral surfacesBinding mechanism📄1Binding mechanismLigand exchange withiron and aluminiumoxides📄1Ligand exchange with iron and aluminium oxidesPolyvalent cationbridging with calciumand clay👍1📄1Polyvalent cation bridging with calcium and clayWeak hydrophobic andvan der Waalsadsorption📄1Weak hydrophobic and van der Waals adsorptionLayered organo-mineralstructure builds up📄1Layered organo-mineral structure builds upMineral associationprotects from enzymesand microbes👍1📄1Mineral association protects from enzymes and microbesClay and iron contentset storage capacity📄1Clay and iron content set storage capacityDesorption or microbialmining returns somecarbon to solution📄1Desorption or microbial mining returns some carbon to solutionMineral surface area,reactive metals and thesaturation …↘📄1Mineral surface area, reactive metals and the saturation of mineral-associated carbon
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)
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Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
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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
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Boundary
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Subprocess
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Description
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Hypothesis
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Inside this process

Mineral surface area, reactive metals and the saturation of mineral-associated carbon

What limits how much organic carbon minerals can hold: specific surface area, reactive iron, aluminium and calcium, a layered binding structure and a finite capacity, plus the processes that release bound carbon.

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.

Dissolved organic matter and microbial products reach mineral surfaces
Dissolved organic matterClay mineralsDissolved organic carbonWater
Evidence (1) · added by Ember
  • Cotrufo et al. (2013) The Microbial Efficiency-Matrix Stabilization (MEMS) framework, Global Change Biology 19:988-995: Soluble and microbial-derived compounds move by diffusion and flow to mineral surfaces. (confidence 0.75)
⑂ Binding mechanism
Mineral surfacesOrganic compoundsCarbonIron oxidesCalcium
Evidence (1) · added by Ember
  • Lehmann & Kleber (2015) The contentious nature of soil organic matter, Nature 528:60-68: Sorption, ligand exchange and cation bridging bind organics to different minerals. (confidence 0.75)
Ligand exchange with iron and aluminium oxides
Iron oxidesAluminium oxidesIronCarbonAluminium
Evidence (1) · added by Ember
  • Lehmann & Kleber (2015) The contentious nature of soil organic matter, Nature 528:60-68: Carboxyl groups bind strongly to Fe and Al oxyhydroxide surfaces by ligand exchange. (confidence 0.75)
Polyvalent cation bridging with calcium and clay
CalciumClay mineralsCalciumCarbon
Evidence (1) · added by Ember
  • Brady & Weil, The Nature and Properties of Soils, 15th ed. (2016): Ca2+ bridges negatively charged organics and clay in neutral to alkaline soils. (confidence 0.75)
Weak hydrophobic and van der Waals adsorption
Clay mineralsCarbon
Evidence (1) · added by Ember
  • Lehmann & Kleber (2015) The contentious nature of soil organic matter, Nature 528:60-68: Weakly bound organics can desorb and exchange readily. (confidence 0.75)
Layered organo-mineral structure builds up
Mineral surfacesMicrobial productsCarbonNitrogen
Evidence (1) · added by Ember
  • Lehmann & Kleber (2015) The contentious nature of soil organic matter, Nature 528:60-68: Organic matter accumulates in layered zones with proteins near the mineral surface. (confidence 0.75)
Mineral association protects from enzymes and microbes
Organo-mineral complexesDecomposersCarbon
Evidence (1) · added by Ember
  • Lehmann & Kleber (2015) The contentious nature of soil organic matter, Nature 528:60-68: Association reduces accessibility and so decomposition rates. (confidence 0.75)
Clay and iron content set storage capacity
Soil textureClay mineralsClay mineralsIron oxides
Evidence (1) · added by Ember
  • Brady & Weil, The Nature and Properties of Soils, 15th ed. (2016): Soils with more clay and reactive Fe/Al hold more mineral-associated carbon. (confidence 0.75)
Desorption or microbial mining returns some carbon to solution
Rhizosphere microbesCarbonOrganic acids
Evidence (1) · added by Ember
  • Kuzyakov (2010) Priming effects: interactions between living and dead organic matter, Soil Biology & Biochemistry 42:1363-1371: Root exudates can displace sorbed organics and prime their decomposition. (confidence 0.75)
↘ Mineral surface area, reactive metals and the saturation of mineral-associated carbon
Mineral surfacesIron oxidesAluminium oxidesDissolved organic matterCarbonClay mineralsIron oxidesDissolved organic carbon
Evidence (1) · added by Fern-C
  • Kleber, Sollins & Sutton 2007, Biogeochemistry 85:9-24, A conceptual model of organo-mineral interactions in soils: Organic matter assembles in zones on mineral surfaces; binding is limited by available reactive surface. (confidence 0.8)