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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Bacteria and archaea / Methane cycle: methanogenesis and methanotrophy

Methane cycle: methanogenesis and methanotrophy

Where soil methane comes from and where it goes. Methanogenic archaea make CH4 in strictly anoxic microsites after other electron acceptors are used up, and methanotrophs oxidize it in oxic zones; the balance sets whether a soil is a methane source or sink.

Boundary: where this process starts

Starts with: Methanogenesis starts only after Nitrate, Mn(IV), Fe(III) and Sulfate are depleted, at Eh below about -150 to -200 mV

Boundary: where it ends

Ends after: Methanotrophs oxidize Methane with methane monooxygenase in oxic layers and the rhizosphere, consuming roughly 20-80% of the methane produced (midpoint about 50% in paddies); Methane reaches the surface by diffusion, bubbling or plant aerenchyma (in rice, over 90% of emitted CH4 passes through the plants)

PARTICIPANTSRESOURCESMethanogenicarchaeaMethanotrophicbacteriaFermentingbacteriaMethanosarcinaMethanosaetaOtherparticipantsMethaneCarbon dioxideOxygenAcetateHydrogenImpact +3 of 5. Click for details and evidence.Anoxia and depleted electronImpact -2 of 5. Click for details and evidence.Oxic upland soilImpact +3 of 5. Click for details and evidence.Methanogens select substrateImpact +3 of 5. Click for details and evidence.65% acetateImpact +3 of 5. Click for details and evidence.35% H2 plus CO2Impact +2 of 5. Click for details and evidence.Rates follow temperatureImpact +2 of 5. Click for details and evidence.Rates follow temperatureImpact +3 of 5. Click for details and evidence.Methane moves toward the surImpact -4 of 5. Click for details and evidence.Oxic layers and root-zone oxImpact +1 of 5. Click for details and evidence.↻ reinforces · weak · 0.05 More methane warmImpact -3 of 5. Click for details and evidence.Residual methane emittedImpact -3 of 5. Click for details and evidence.Unoxidized methane reaches tImpact +2 of 5. Click for details and evidence.Atmospheric methane removedMethanogenesis starts only after Nitrate, Mn(IV), Fe(III) and Sulfate are depleted, at Eh below about -150 to -200 mV: makes MethanemakesWhich substrate feeds methanogenesis (roughly two thirds acetate, one third H2 plus CO2 in moderate-temperature paddy and sediment; bogs shift toward H2/CO2): uses up Carbon dioxideuses upWhich substrate feeds methanogenesis (roughly two thirds acetate, one third H2 plus CO2 in moderate-temperature paddy and sediment; bogs shift toward H2/CO2): uses up Acetateuses upWhich substrate feeds methanogenesis (roughly two thirds acetate, one third H2 plus CO2 in moderate-temperature paddy and sediment; bogs shift toward H2/CO2): uses up Hydrogenuses upAcetoclastic methanogens (Methanosarcina, Methanosaeta) split Acetate into Methane and Carbon dioxide: makes MethanemakesAcetoclastic methanogens (Methanosarcina, Methanosaeta) split Acetate into Methane and Carbon dioxide: makes Carbon dioxidemakesAcetoclastic methanogens (Methanosarcina, Methanosaeta) split Acetate into Methane and Carbon dioxide: uses up Acetateuses upHydrogenotrophic methanogens reduce Carbon dioxide with Hydrogen supplied by syntrophic fermenters (H2 must stay at a few Pa): makes MethanemakesHydrogenotrophic methanogens reduce Carbon dioxide with Hydrogen supplied by syntrophic fermenters (H2 must stay at a few Pa): uses up Carbon dioxideuses upHydrogenotrophic methanogens reduce Carbon dioxide with Hydrogen supplied by syntrophic fermenters (H2 must stay at a few Pa): uses up Hydrogenuses upMethanogenesis is more temperature sensitive than methane oxidation (Q10 about 2-4 versus 1.5-2), so warming favours emission: uses MethaneMethane reaches the surface by diffusion, bubbling or plant aerenchyma (in rice, over 90% of emitted CH4 passes through the plants): uses MethaneMethane reaches the surface by diffusion, bubbling or plant aerenchyma (in rice, over 90% of emitted CH4 passes through the plants): uses OxygenMethanotrophs oxidize Methane with methane monooxygenase in oxic layers and the rhizosphere, consuming roughly 20-80% of the methane produced (midpoint about 50% in paddies): uses up Methaneuses upMethanotrophs oxidize Methane with methane monooxygenase in oxic layers and the rhizosphere, consuming roughly 20-80% of the methane produced (midpoint about 50% in paddies): uses Carbon dioxideMethanotrophs oxidize Methane with methane monooxygenase in oxic layers and the rhizosphere, consuming roughly 20-80% of the methane produced (midpoint about 50% in paddies): uses up Oxygenuses upAerated upland soils with high-affinity methanotrophs take up atmospheric Methane: global soil sink about 30 Tg CH4 per year (range 11-49): uses up Methaneuses upAerated upland soils with high-affinity methanotrophs take up atmospheric Methane: global soil sink about 30 Tg CH4 per year (range 11-49): uses Oxygenproduced once electronacceptors goneMethane: produced once electron acceptors gonereduced to methaneCarbon dioxide: reduced to methaneone of two methanogenicsubstratesAcetate: one of two methanogenic substratesfeeds hydrogenotrophicmethanogensHydrogen: feeds hydrogenotrophic methanogensformed from acetatecleavageMethane: formed from acetate cleavageformed from acetatecleavageCarbon dioxide: formed from acetate cleavagesplit into methane andCO2Acetate: split into methane and CO2formed from CO2reductionMethane: formed from CO2 reductionreduced to methaneCarbon dioxide: reduced to methaneconsumed by methanogensHydrogen: consumed by methanogensemission rises withwarmingMethane: emission rises with warmingtransported to surfaceMethane: transported to surfacemeets methane in oxiclayerOxygen: meets methane in oxic layeroxidised bymonooxygenaseMethane: oxidised by monooxygenasereleased by methaneoxidationCarbon dioxide: released by methane oxidationsupplies methanotrophoxidationOxygen: supplies methanotroph oxidationtaken up from atmosphereMethane: taken up from atmosphereenables high-affinityuptakeOxygen: enables high-affinity uptakeStart: Methane cycle:methanogenesis andmethanotrophySTARTStart: Methane cycle: methanogenesis and methanotrophyEnd: Methane cycle:methanogenesis andmethanotrophyENDEnd: Methane cycle: methanogenesis and methanotrophyMethanogenesis startsonly after Nitrate,Mn(IV), Fe(III) a…📄1Methanogenesis starts only after Nitrate, Mn(IV), Fe(III) and Sulfate are depleted, at Eh below about -150 to -200 mVWhich substrate feedsmethanogenesis (roughlytwo thirds acetate, o…📄1Which substrate feeds methanogenesis (roughly two thirds acetate, one third H2 plus CO2 in moderate-temperature paddy and sediment; bogs shift toward H2/CO2)Acetoclasticmethanogens(Methanosarcin…📄1Acetoclastic methanogens (Methanosarcina, Methanosaeta) split Acetate into Methane and Carbon dioxideHydrogenotrophicmethanogens reduceCarbon dioxide wi…📄1Hydrogenotrophic methanogens reduce Carbon dioxide with Hydrogen supplied by syntrophic fermenters (H2 must stay at a few Pa)Methanogenesis is moretemperature sensitivethan methane oxidati…📄1Methanogenesis is more temperature sensitive than methane oxidation (Q10 about 2-4 versus 1.5-2), so warming favours emissionMethane reaches thesurface by diffusion,bubbling or pla…📄1Methane reaches the surface by diffusion, bubbling or plant aerenchyma (in rice, over 90% of emitted CH4 passes through the plants)Methanotrophs oxidizeMethane with methanemonooxygenase in ox…📄1Methanotrophs oxidize Methane with methane monooxygenase in oxic layers and the rhizosphere, consuming roughly 20-80% of the methane produced (midpoint about 50% in paddies)Aerated upland soilswith high-affinitymethanotrophs take …📄1Aerated upland soils with high-affinity methanotrophs take up atmospheric Methane: global soil sink about 30 Tg CH4 per year (range 11-49)
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.

Methanogenesis starts only after Nitrate, Mn(IV), Fe(III) and Sulfate are depleted, at Eh below about -150 to -200 mV
Methanogenic archaeaNitrateSulfateMethane
Evidence (1) · added by Ember
  • Peters & Conrad 1996, Soil Biology and Biochemistry 28:371, Sequential reduction processes and initiation of CH4 production upon flooding of oxic upland soils: After flooding, nitrate, Mn(IV), Fe(III) and sulfate reduction precede CH4 production, which begins at low redox potential. (confidence 0.8)
⑂ Which substrate feeds methanogenesis (roughly two thirds acetate, one third H2 plus CO2 in moderate-temperature paddy and sediment; bogs shift toward H2/CO2)
Methanogenic archaeaFermenting bacteriaAcetateHydrogenCarbon dioxide
Evidence (1) · added by Ember
  • Conrad 1999, FEMS Microbiology Ecology 28:193, Contribution of hydrogen to methane production and control of hydrogen concentrations in methanogenic soils and sediments: In anoxic soils at moderate temperature about two thirds of CH4 derives from acetate and one third from H2/CO2; estimate varies with temperature and pH. (confidence 0.6)
Acetoclastic methanogens (Methanosarcina, Methanosaeta) split Acetate into Methane and Carbon dioxide
MethanosarcinaMethanosaetaAcetateMethaneCarbon dioxide
Evidence (1) · added by Ember
  • Conrad 1999, FEMS Microbiology Ecology 28:193: Acetoclastic methanogenesis is the main route in most flooded soils. (confidence 0.75)
Hydrogenotrophic methanogens reduce Carbon dioxide with Hydrogen supplied by syntrophic fermenters (H2 must stay at a few Pa)
Hydrogenotrophic methanogensSyntrophic bacteriaHydrogenCarbon dioxideMethane
Evidence (1) · added by Ember
  • Stams & Plugge 2009, Nature Reviews Microbiology 7:568, Electron transfer in syntrophic communities of anaerobic bacteria and archaea: Fermenters can only oxidize their substrates when methanogens keep H2 partial pressure very low. (confidence 0.8)
Methanogenesis is more temperature sensitive than methane oxidation (Q10 about 2-4 versus 1.5-2), so warming favours emission
Methanogenic archaeaMethanotrophic bacteriaHeatMethaneHeat
Evidence (1) · added by Ember
  • Segers 1998, Biogeochemistry 41:23, Methane production and methane consumption: a review of processes underlying wetland methane fluxes: Reported Q10 values for CH4 production are mostly higher than for CH4 consumption. (confidence 0.6)
Methane reaches the surface by diffusion, bubbling or plant aerenchyma (in rice, over 90% of emitted CH4 passes through the plants)
Rice plantsGas bubblesMethaneOxygen
Evidence (1) · added by Ember
  • Butterbach-Bahl, Papen & Rennenberg 1997, Plant, Cell and Environment 20:1175, Impact of gas transport through rice cultivars on methane emission from rice paddy fields: Plant-mediated transport accounted for the large majority of CH4 emission from rice paddies. (confidence 0.65)
Methanotrophs oxidize Methane with methane monooxygenase in oxic layers and the rhizosphere, consuming roughly 20-80% of the methane produced (midpoint about 50% in paddies)
Methanotrophic bacteriaRootsMethaneOxygenCarbon dioxide
Evidence (1) · added by Ember
  • Conrad 2009, Environmental Microbiology Reports 1:285: A large part, often tens of percent up to the majority, of the CH4 produced is oxidized before reaching the atmosphere. (confidence 0.65)
Aerated upland soils with high-affinity methanotrophs take up atmospheric Methane: global soil sink about 30 Tg CH4 per year (range 11-49)
Upland soilsHigh-affinity methanotrophsMethaneOxygen
Evidence (1) · added by Ember
  • Saunois et al. 2020, Earth System Science Data 12:1561, The Global Methane Budget 2000-2017: Soil uptake in the 2008-2017 budget is about 30 (11-49) Tg CH4 per year. (confidence 0.8)