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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Biological coupling: organic matter and soil food web

Biological coupling: organic matter and soil food web

How plant litter, roots, fungi, bacteria and fauna together decompose organic matter and build stable soil carbon. Covers the soil food web and the disturbance forks that tip soil toward carbon gain or loss.

Boundary: where this process starts

Starts with: Plant litter and root inputs enter the soil

Boundary: where it ends

Ends after: Net soil carbon gain: stable organic matter increases; Net soil carbon loss: respiration exceeds inputs

PARTICIPANTSRESOURCESPlant rootsSoil microbesSoil faunaFungiDecomposerfungiOtherparticipantsCarbonSoil organicmatterPlant litterNitrogenCarbon dioxideImpact +4 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.carbon allocated to fungal pImpact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.microbial carbon use efficieImpact +3 of 5. Click for details and evidence.microbes eatenImpact +2 of 5. Click for details and evidence.released ammonium near rootsImpact 03 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.55% stable conditions with hImpact -4 of 5. Click for details and evidence.45% warming, tillage or drouImpact +4 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.↻ reinforces · moderate · 0.2 Warming and diImpact -3 of 5. Click for details and evidence.↻ balances · moderate · 0.3 Mineral protectiImpact +3 of 5. Click for details and evidence.↻ reinforces · moderate · 0.3 Fungal nutrienImpact +2 of 5. Click for details and evidence.↻ reinforces · weak · 0.15 Predation keeps dPlant litter and root inputs enter the soil: makes CarbonmakesPlant litter and root inputs enter the soil: uses Plant litterFauna shred and mix litter (earthworms, collembola, mites, termites): uses Soil organic matterFauna shred and mix litter (earthworms, collembola, mites, termites): uses up Plant litteruses upFungi and bacteria decompose litter, releasing CO2 and nutrients: uses up Plant litteruses upFungi and bacteria decompose litter, releasing CO2 and nutrients: makes NitrogenmakesFungi and bacteria decompose litter, releasing CO2 and nutrients: makes Carbon dioxidemakesMicrobial necromass and metabolites bind to minerals as stable organic matter: uses up Carbonuses upMicrobial necromass and metabolites bind to minerals as stable organic matter: makes Soil organic mattermakesPredators graze microbes (protozoa, nematodes) and release nutrients: makes NitrogenmakesMycorrhizal fungi trade nutrients and water for plant carbon: uses up Carbonuses upMycorrhizal fungi trade nutrients and water for plant carbon: uses NitrogenDisturbance or stress to soil biology: uses CarbonDisturbance or stress to soil biology: uses Soil organic matterNet soil carbon gain: stable organic matter increases: makes CarbonmakesNet soil carbon gain: stable organic matter increases: makes Soil organic mattermakesNet soil carbon loss: respiration exceeds inputs: uses up Soil organic matteruses upNet soil carbon loss: respiration exceeds inputs: makes Carbon dioxidemakesintroduced to soilCarbon: introduced to soiladded to soil surfacePlant litter: added to soil surfaceincorporated into soilmixSoil organic matter: incorporated into soil mixshredded and mixedPlant litter: shredded and mixeddecomposed by fungi andbacteriaPlant litter: decomposed by fungi and bacteriamineralized and releasedNitrogen: mineralized and releasedreleased by decayCarbon dioxide: released by decaystabilized inmineral-bound poolCarbon: stabilized in mineral-bound poolstabilized on mineralsurfacesSoil organic matter: stabilized on mineral surfacesreleased by grazingNitrogen: released by grazingexchanged for nutrientsCarbon: exchanged for nutrientsdelivered to plant rootsNitrogen: delivered to plant rootslost or redistributedCarbon: lost or redistributeddestabilized by stressSoil organic matter: destabilized by stressstored in soilCarbon: stored in soilaccumulates in soilSoil organic matter: accumulates in soildepleted bydecompositionSoil organic matter: depleted by decompositionlost from soilCarbon dioxide: lost from soilStart: Biologicalcoupling: organicmatter and soil fo…STARTStart: Biological coupling: organic matter and soil food webEnd: Biologicalcoupling: organicmatter and soil fo… ↗3ENDEnd: Biological coupling: organic matter and soil food webPlant litter and rootinputs enter the soil📄1Plant litter and root inputs enter the soilFauna shred and mixlitter (earthworms,collembola, mite…👍1📄1Fauna shred and mix litter (earthworms, collembola, mites, termites)Fungi and bacteriadecompose litter,releasing CO2 a…📄1Fungi and bacteria decompose litter, releasing CO2 and nutrientsMicrobial necromass andmetabolites bind tominerals as stab…👍1📄1Microbial necromass and metabolites bind to minerals as stable organic matterPredators grazemicrobes (protozoa,nematodes) and relea…👍1📄1Predators graze microbes (protozoa, nematodes) and release nutrientsMycorrhizal fungi tradenutrients and water forplant carbon👍1📄1Mycorrhizal fungi trade nutrients and water for plant carbonDisturbance or stressto soil biology📄1Disturbance or stress to soil biologyNet soil carbon gain:stable organic matterincreases👍1📄1Net soil carbon gain: stable organic matter increasesNet soil carbon loss:respiration exceedsinputs📄1Net soil carbon loss: respiration exceeds inputs
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.

Plant litter and root inputs enter the soil
PlantsPlant rootsPlant litterCarbonRoot exudates
Evidence (1) · added by Fern
  • Bardgett, The Biology of Soil (2005); Clemmensen et al. (2013) Science 339:1615-1618: Roots contribute a large share of soil carbon inputs, through litter, exudates and fungal partners. (confidence 0.85)
Fauna shred and mix litter (earthworms, collembola, mites, termites)
EarthwormsCollembolaMitesTermitesPlant litterSoil organic matter
Evidence (1) · added by Fern
  • Lavelle & Spain (2001); Swift, Heal & Anderson, Decomposition in Terrestrial Ecosystems (1979): Soil fauna fragment litter and increase microbial access. (confidence 0.9)
Fungi and bacteria decompose litter, releasing CO2 and nutrients
Decomposer fungiDecomposer bacteriaPlant litterCarbon dioxideOxygenNitrogen
Evidence (1) · added by Fern
  • Swift et al. (1979); Paul (2015): Microbes carry out most decomposition and mineralisation; fungi dominate lignocellulose breakdown. (confidence 0.9)
Microbial necromass and metabolites bind to minerals as stable organic matter
Microbial necromassClay mineralsIron oxidesSoil organic matterCarbonClay minerals
Evidence (1) · added by Fern
  • Cotrufo et al. (2013) Nature Geoscience 6:989-994; Lehmann & Kleber (2015) Nature 528:60-68: Mineral-associated organic matter is mainly microbial-derived; stability stems from mineral association and protection, not molecular recalcitrance. (confidence 0.85)
Predators graze microbes (protozoa, nematodes) and release nutrients
ProtozoaBacterial-feeding nematodesFungal-feeding nematodesNitrogenBacteriaAmmonium
Evidence (1) · added by Fern
  • Clarholm (1985); Bonkowski (2004) New Phytologist 162:617-631: Grazing stimulates microbial turnover and releases ammonium near roots (microbial loop). (confidence 0.85)
Mycorrhizal fungi trade nutrients and water for plant carbon
Arbuscular mycorrhizal fungiEctomycorrhizal fungiPlant rootsCarbonPhosphorusNitrogenWater
Evidence (1) · added by Fern
  • Smith & Read (2008); Kiers et al. (2011) Science 333:880-882: Plants allocate carbon (about 4-20% of photosynthate) to fungi that return P, N and water. (confidence 0.85)
⑂ Disturbance or stress to soil biology
Soil microbesDroughtTillageWarmingSoil organic matterCarbon
Evidence (1) · added by Fern
  • Davidson & Janssens (2006) Nature 440:165-173; Bardgett (2005): Soil carbon balance depends on whether inputs or respiration losses increase under change. (confidence 0.7)
Net soil carbon gain: stable organic matter increases
Soil organic matterSoil organic matterCarbon
Evidence (1) · added by Fern
  • Lal (2004) Science 304:1623-1627: Where inputs exceed decomposition, soil carbon builds. (confidence 0.8)
Net soil carbon loss: respiration exceeds inputs
Decomposer bacteriaDecomposer fungiSoil organic matterCarbon dioxide
Evidence (1) · added by Fern
  • Davidson & Janssens (2006): Warming and disturbance can raise decomposition faster than inputs. (confidence 0.75)