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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Humification and SOM stabilization / Microbial necromass pathway to stable organic matter / Carbon use efficiency controls necromass production

Carbon use efficiency controls necromass production

Carbon use efficiency sets how much taken-up carbon becomes biomass and necromass rather than carbon dioxide. Substrate quality, nutrient limitation and temperature change it, with warming and acclimation shaping the soil carbon response.

Boundary: where this process starts

Starts with: Microbes take up substrate and split carbon between respiration and biomass synthesis (anabolism)

Boundary: where it ends

Ends after: High CUE (about 0.5-0.6) shunts more carbon into biomass and necromass; Lower necromass inputs and more respiration reduce soil carbon

PARTICIPANTSRESOURCESSoil microbesTemperatureAtmosphereCarbonCarbon dioxideTemperatureImpact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.N-rich or labile substrateImpact -3 of 5. Click for details and evidence.poor substrate or stressImpact -2 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.Respired CO2 adds to atmosphImpact -3 of 5. Click for details and evidence.↻ reinforces · weak · 0.1 Warming further loImpact +4 of 5. Click for details and evidence.More biomass and necromassImpact -3 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.Sustained warming triggers aImpact +2 of 5. Click for details and evidence.↻ balances · moderate · 0.3 Acclimation limiImpact +2 of 5. Click for details and evidence.Carbon split moves back towaMicrobes take up substrate and split carbon between respiration and biomass synthesis (anabolism): uses up Carbonuses upMicrobes take up substrate and split carbon between respiration and biomass synthesis (anabolism): makes Carbon dioxidemakesHigh CUE (about 0.5-0.6) shunts more carbon into biomass and necromass: uses up Carbonuses upLow CUE (about 0.2-0.3) from poor-quality substrate, nutrient limitation or heat sends more carbon to CO2: uses up Carbonuses upLow CUE (about 0.2-0.3) from poor-quality substrate, nutrient limitation or heat sends more carbon to CO2: makes Carbon dioxidemakesWarming lowers CUE in models by about 0.016 per degree Celsius: uses CarbonWarming lowers CUE in models by about 0.016 per degree Celsius: uses TemperatureLower necromass inputs and more respiration reduce soil carbon: uses up Carbonuses upLower necromass inputs and more respiration reduce soil carbon: makes Carbon dioxidemakesMore CO2 to the atmosphere adds to warming: uses Carbon dioxideMore CO2 to the atmosphere adds to warming: uses TemperatureMicrobial thermal acclimation and substrate depletion partly restore CUE under sustained warming: uses CarbonMicrobial thermal acclimation and substrate depletion partly restore CUE under sustained warming: uses Carbon dioxidesplit betweenrespiration a…Carbon: split between respiration and anabolismreleased fromrespirationCarbon dioxide: released from respirationshunted into biomass andnecromassCarbon: shunted into biomass and necromassrespired under poorconditionsCarbon: respired under poor conditionssent by low efficiencyCarbon dioxide: sent by low efficiencypartitioned less towardbiomassCarbon: partitioned less toward biomasslowers efficiency inmodelsTemperature: lowers efficiency in modelslost from soil poolsCarbon: lost from soil poolsrespired instead ofstoredCarbon dioxide: respired instead of storedaccumulates inatmosphereCarbon dioxide: accumulates in atmosphereamplified by atmosphericwarmingTemperature: amplified by atmospheric warminguse efficiency adjustsover timeCarbon: use efficiency adjusts over timerespired under sustainedwarmingCarbon dioxide: respired under sustained warmingStart: Substrate takenup by microbesSTARTStart: Substrate taken up by microbesEnd: Carbon splitbetween biomass andrespiration setENDEnd: Carbon split between biomass and respiration setMicrobes take upsubstrate and splitcarbon betwe…📄1Microbes take up substrate and split carbon between respiration and biomass synthesis (anabolism)High CUE (about0.5-0.6) shunts morecarbon into biomass a…📄1High CUE (about 0.5-0.6) shunts more carbon into biomass and necromassLow CUE (about 0.2-0.3)from poor-qualitysubstrate, nutrie…👍2📄1Low CUE (about 0.2-0.3) from poor-quality substrate, nutrient limitation or heat sends more carbon to CO2Warming lowers CUE inmodels by about 0.016per degree Celsius👍1📄1Warming lowers CUE in models by about 0.016 per degree CelsiusLower necromass inputsand more respirationreduce soil carbon📄1Lower necromass inputs and more respiration reduce soil carbonMore CO2 to theatmosphere adds towarming📄1More CO2 to the atmosphere adds to warmingMicrobial thermalacclimation andsubstrate depleti…📄2Microbial thermal acclimation and substrate depletion partly restore CUE under sustained warming
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.

Microbes take up substrate and split carbon between respiration and biomass synthesis (anabolism)
Soil microbesCarbonCarbon dioxide
Evidence (1) · added by Ember
  • Liang, Schimel & Jastrow 2017, The importance of anabolism in microbial control over soil carbon storage, Nature Microbiology 2:17105: Anabolism increases the microbial contribution to stable soil carbon (confidence 0.8)
High CUE (about 0.5-0.6) shunts more carbon into biomass and necromass
Soil microbesCarbon
Evidence (1) · added by Ember
  • Sinsabaugh et al. 2013, Carbon use efficiency of microbial communities: stoichiometry, methodology and modelling, Ecology Letters 16:930-939: Community CUE ranges roughly 0.3-0.6; high-quality, N-rich substrate raises it (confidence 0.7)
Low CUE (about 0.2-0.3) from poor-quality substrate, nutrient limitation or heat sends more carbon to CO2
Soil microbesCarbon dioxideCarbon
Evidence (1) · added by Ember
  • Sinsabaugh et al. 2013, Carbon use efficiency of microbial communities: stoichiometry, methodology and modelling, Ecology Letters 16:930-939: Low CUE under nutrient imbalance (confidence 0.6)
Warming lowers CUE in models by about 0.016 per degree Celsius
TemperatureSoil microbesTemperatureCarbon
Evidence (1) · added by Ember
  • Allison, Wallenstein & Bradford 2010, Soil-carbon response to warming dependent on microbial physiology, Nature Geoscience 3:336-340: Model assumed CUE declining with temperature, value used about 0.016 per degree, estimate not measured everywhere (confidence 0.5)
Lower necromass inputs and more respiration reduce soil carbon
Soil microbesCarbon dioxideCarbon
Evidence (1) · added by Ember
  • Allison, Wallenstein & Bradford 2010, Soil-carbon response to warming dependent on microbial physiology, Nature Geoscience 3:336-340: Lower CUE leads to lower microbial biomass and soil carbon (confidence 0.6)
More CO2 to the atmosphere adds to warming
AtmosphereCarbon dioxideTemperature
Evidence (1) · added by Ember
  • Davidson & Janssens 2006, Temperature sensitivity of soil carbon decomposition and feedbacks to climate change, Nature 440:165-173: Soil carbon decomposition feedback to climate (confidence 0.65)
Microbial thermal acclimation and substrate depletion partly restore CUE under sustained warming
Soil microbesTemperatureCarbonCarbon dioxide
Evidence (2) · added by Ember-D
  • Frey, Lee, Melillo & Six (2013) Nature Climate Change 3:395-398, The temperature response of soil microbial efficiency and its feedback to climate: After long-term warming the CUE response to temperature was small or absent, contrary to a constant decline (confidence 0.8)
  • Tucker, Bell, Pendall & Ogle (2013) Global Change Biology 19:252-263: Declining CUE explains only part of thermal acclimation of soil respiration (confidence 0.7)