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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Roots and rhizosphere / Root exudate chemistry, fate and priming / Exudate priming and microbial nitrogen mining

Exudate priming and microbial nitrogen mining

A pulse of labile carbon from roots activates microbes, which may mine native organic matter for nitrogen and respire extra soil carbon (positive priming) or switch to the easy substrate (negative priming). Plant nitrogen uptake and microbial nitrogen limitation feed back on the process.

Boundary: where this process starts

Starts with: Labile carbon surge activates dormant r-strategist microbes and enzyme synthesis

Boundary: where it ends

Ends after: Priming outcome in the rhizosphere; Negative priming: microbes switch to the easy substrate and spare soil organic matter

PARTICIPANTSRESOURCESRhizospheremicrobesSoil organicmatterPlant rootsPlantsCarbonNitrogenSoil organicmatterAmmoniumEnzymesImpact +4 of 5. Click for details and evidence.Pulse arrivesImpact +3 of 5. Click for details and evidence.High C:N exudateImpact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.60% positiveImpact -2 of 5. Click for details and evidence.15% negativeImpact 01 of 5. Click for details and evidence.25% no net effect or apparenImpact +3 of 5. Click for details and evidence.Mineral N pulseImpact -3 of 5. Click for details and evidence.SOM decompositionImpact +3 of 5. Click for details and evidence.Root N uptakeImpact +3 of 5. Click for details and evidence.↻ reinforces · moderate · 0.3 More photosyntImpact +3 of 5. Click for details and evidence.Mined N lifts limitationImpact -3 of 5. Click for details and evidence.↻ balances · moderate · 0.35 Less N mining aImpact +2 of 5. Click for details and evidence.SOM sparedImpact -3 of 5. Click for details and evidence.Carbon releasedImpact +3 of 5. Click for details and evidence.Plant nutrition improvedLabile carbon surge activates dormant r-strategist microbes and enzyme synthesis: uses CarbonLabile carbon surge activates dormant r-strategist microbes and enzyme synthesis: makes EnzymesmakesMicrobes mine native organic matter for nitrogen when exudate carbon-to-nitrogen ratio is high: uses CarbonMicrobes mine native organic matter for nitrogen when exudate carbon-to-nitrogen ratio is high: uses NitrogenMicrobes mine native organic matter for nitrogen when exudate carbon-to-nitrogen ratio is high: uses up Soil organic matteruses upPriming outcome in the rhizosphere: uses CarbonPriming outcome in the rhizosphere: uses Soil organic matterPositive priming: extra ammonium and DOC released, plant nitrogen uptake rises: uses NitrogenPositive priming: extra ammonium and DOC released, plant nitrogen uptake rises: makes AmmoniummakesSoil organic carbon lost as CO2 through priming: uses up Soil organic matteruses upNegative priming: microbes switch to the easy substrate and spare soil organic matter: uses Soil organic matterPlant nitrogen uptake raises photosynthesis and exudation: makes CarbonmakesPlant nitrogen uptake raises photosynthesis and exudation: uses up Nitrogenuses upMined nitrogen relieves microbial N limitation: uses NitrogenRoots compete with microbes for the released ammonium and nitrate: uses up Ammoniumuses uptriggers microbialgrowth responseCarbon: triggers microbial growth responsesynthesized by activatedmicrobesEnzymes: synthesized by activated microbessupplies energy forminingCarbon: supplies energy for miningmined from organicmatterNitrogen: mined from organic matterdecomposed for nitrogenSoil organic matter: decomposed for nitrogenshifts with primingoutcomeCarbon: shifts with priming outcomefate set by primingdirectionSoil organic matter: fate set by priming directiontaken up by plant rootsNitrogen: taken up by plant rootsreleased by primedmicrobesAmmonium: released by primed microbeslost through primingSoil organic matter: lost through primingspared fromdecompositionSoil organic matter: spared from decompositionfixed and exuded byplantCarbon: fixed and exuded by planttaken up to supportgrowthNitrogen: taken up to support growthrelieves microbialnitrogen limitationNitrogen: relieves microbial nitrogen limitationtaken up by rootsAmmonium: taken up by rootsStart: Labile carbonpulse reaches microbesSTARTStart: Labile carbon pulse reaches microbesEnd: Native organicmatter decompositionalteredENDEnd: Native organic matter decomposition alteredLabile carbon surgeactivates dormantr-strategist microb…📄1Labile carbon surge activates dormant r-strategist microbes and enzyme synthesisMicrobes mine nativeorganic matter fornitrogen when exuda…📄1Microbes mine native organic matter for nitrogen when exudate carbon-to-nitrogen ratio is highPriming outcome in therhizosphere📄2Priming outcome in the rhizospherePositive priming: extraammonium and DOCreleased, pla…👍1📄1Positive priming: extra ammonium and DOC released, plant nitrogen uptake risesSoil organic carbonlost as CO2 throughpriming📄1Soil organic carbon lost as CO2 through primingNegative priming:microbes switch to theeasy substrate a…📄1Negative priming: microbes switch to the easy substrate and spare soil organic matterPlant nitrogen uptakeraises photosynthesisand exudation📄1Plant nitrogen uptake raises photosynthesis and exudationMined nitrogen relievesmicrobial N limitation📄1Mined nitrogen relieves microbial N limitationRoots compete withmicrobes for thereleased ammonium a…📄1Roots compete with microbes for the released ammonium and nitrate
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.

Labile carbon surge activates dormant r-strategist microbes and enzyme synthesis
Rhizosphere microbesCarbonEnzymes
Evidence (1) · added by Ember
  • Blagodatskaya & Kuzyakov 2008, Mechanisms of real and apparent priming effects, Biol Fertil Soils 45:115-131: Real priming is driven by raised enzyme production and microbial activation after labile input (confidence 0.75)
Microbes mine native organic matter for nitrogen when exudate carbon-to-nitrogen ratio is high
Rhizosphere microbesSoil organic matterNitrogenSoil organic matterCarbon
Evidence (1) · added by Ember
  • Craine, Morrow & Fierer 2007, Microbial nitrogen limitation increases decomposition, Ecology 88:2105-2113: Microbial N limitation increases decomposition in 26 grassland soils (N mining) (confidence 0.75)
⑂ Priming outcome in the rhizosphere
Rhizosphere microbesSoil organic matterCarbon
Evidence (2) · added by Ember
  • Cheng et al. 2014, Synthesis and modeling perspectives of rhizosphere priming, New Phytologist 201:31-44: Synthesis finds positive priming most common but negative and zero outcomes exist; shares are estimates (positive 50-70%) (confidence 0.5)
  • Kuzyakov 2010, Priming effects: interactions between living and dead organic matter, Soil Biol Biochem 42:1363-1371: Priming can be positive, negative or apparent (confidence 0.7)
Positive priming: extra ammonium and DOC released, plant nitrogen uptake rises
Rhizosphere microbesPlant rootsAmmoniumNitrogen
Evidence (1) · added by Ember
  • Phillips, Finzi & Bernhardt 2011, Enhanced root exudation induces microbial feedbacks to N cycling in a pine forest under long-term CO2 fumigation, Ecology Letters 14:187-194: Elevated exudation in a pine forest raised microbial N mining and N availability to trees (confidence 0.75)
Soil organic carbon lost as CO2 through priming
Rhizosphere microbesCarbon dioxideSoil organic matter
Evidence (1) · added by Ember
  • Cheng et al. 2014, Synthesis and modeling perspectives of rhizosphere priming, New Phytologist 201:31-44: Priming raised SOM mineralization by tens of percent in many studies (confidence 0.55)
Negative priming: microbes switch to the easy substrate and spare soil organic matter
Rhizosphere microbesSoil organic matterSugars
Evidence (1) · added by Ember
  • Kuzyakov 2010, Priming effects: interactions between living and dead organic matter, Soil Biol Biochem 42:1363-1371: Preferential substrate utilization lowers SOM decomposition (confidence 0.65)
Plant nitrogen uptake raises photosynthesis and exudation
Plant rootsPlantsNitrogenCarbon
Evidence (1) · added by Ember
  • Phillips, Finzi & Bernhardt 2011, Enhanced root exudation induces microbial feedbacks to N cycling in a pine forest under long-term CO2 fumigation, Ecology Letters 14:187-194: Increased N supply supports further plant carbon fixation and exudation under elevated CO2 (confidence 0.6)
Mined nitrogen relieves microbial N limitation
Rhizosphere microbesNitrogen
Evidence (1) · added by Ember
  • Craine, Morrow & Fierer 2007, Microbial nitrogen limitation increases decomposition, Ecology 88:2105-2113: Alleviating N limitation reduces N-mining decomposition (confidence 0.65)
Roots compete with microbes for the released ammonium and nitrate
Plant rootsRhizosphere microbesAmmoniumNitrate
Evidence (1) · added by Ember
  • Kuzyakov & Xu 2013, Competition between roots and microorganisms for nitrogen, New Phytologist 198:656-669: Roots and microbes compete for mineral N; microbes win in the short term, roots over the long term (confidence 0.75)