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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Terrestrial nutrient cycling / Nitrogen fixation supply-demand feedback

Nitrogen fixation supply-demand feedback

Nitrogen-fixing plants and microbes gain an advantage where soil nitrogen is scarce, add nitrogen to the ecosystem and then lose that advantage as nitrogen accumulates; a balancing loop that tracks nitrogen demand.

Boundary: where this process starts

Starts with: Low soil nitrogen gives nitrogen fixers a competitive advantage

Boundary: where it ends

Ends after: High nitrogen availability switches fixation off and fixers lose their edge

PARTICIPANTSRESOURCESRhizobiaLegume rootsPlantsDecomposersSoil microbesNitrogenDinitrogenAmmoniumCarbonPlant litterImpact -2 of 5. Click for details and evidence.capImpact -4 of 5. Click for details and evidence.↻ balances · strong · 0.5 down-regulation ofImpact +3 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.Impact +3 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.↻ balances · moderate · 0.3 N-rich soil remoImpact 02 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Low soil nitrogen gives nitrogen fixers a competitive advantage: uses NitrogenLow soil nitrogen gives nitrogen fixers a competitive advantage: uses DinitrogenSymbiotic fixers convert Dinitrogen to ammonium, paying with photosynthate: uses up Dinitrogenuses upSymbiotic fixers convert Dinitrogen to ammonium, paying with photosynthate: makes AmmoniummakesSymbiotic fixers convert Dinitrogen to ammonium, paying with photosynthate: uses up Carbonuses upFixer litter and root turnover add nitrogen to the soil: makes NitrogenmakesFixer litter and root turnover add nitrogen to the soil: uses Plant litterSoil mineral nitrogen rises: makes AmmoniummakesHigh nitrogen availability switches fixation off and fixers lose their edge: uses NitrogenHigh nitrogen availability switches fixation off and fixers lose their edge: uses Dinitrogenscarce, favouring fixersNitrogen: scarce, favouring fixersfixed by advantagedfixersDinitrogen: fixed by advantaged fixersconverted to ammonium byfixersDinitrogen: converted to ammonium by fixerssupplied to hostAmmonium: supplied to hostsupplied asphotosynthateCarbon: supplied as photosynthateadded back via turnoverNitrogen: added back via turnoverturns over anddecomposesPlant litter: turns over and decomposesproduced bydecompositionAmmonium: produced by decompositionhigh levels suppressfixationNitrogen: high levels suppress fixationfixation switched offDinitrogen: fixation switched offStart: Nitrogenfixation supply-demandfeedbackSTARTStart: Nitrogen fixation supply-demand feedbackEnd: Nitrogen fixationsupply-demand feedbackENDEnd: Nitrogen fixation supply-demand feedbackLow soil nitrogen givesnitrogen fixers acompetitive advantage📄1Low soil nitrogen gives nitrogen fixers a competitive advantageSymbiotic fixersconvert Dinitrogen toammonium, paying wi…👍1📄1 ↗2Symbiotic fixers convert Dinitrogen to ammonium, paying with photosynthateFixer litter and rootturnover add nitrogento the soil📄1 ↗1Fixer litter and root turnover add nitrogen to the soilSoil mineral nitrogenrises📄1Soil mineral nitrogen risesHigh nitrogenavailability switchesfixation off and fixe…📄1High nitrogen availability switches fixation off and fixers lose their edgePhosphorus andmolybdenum supply cancap fixation👍1📄1Phosphorus and molybdenum supply can cap fixation
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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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.

Low soil nitrogen gives nitrogen fixers a competitive advantage
RhizobiaLegume rootsNitrogenDinitrogen
Evidence (1) · added by Loopa
  • Batterman 2013, Key role of symbiotic dinitrogen fixation in tropical forest secondary succession, Nature, doi:10.1038/nature12525: Fixers dominated young regrowing forests where N was scarce. (confidence 0.8)
Symbiotic fixers convert Dinitrogen to ammonium, paying with photosynthate
RhizobiaLegume rootsDinitrogenCarbonAmmonium
Evidence (1) · added by Loopa
  • Batterman 2013, Key role of symbiotic dinitrogen fixation in tropical forest secondary succession, Nature, doi:10.1038/nature12525: Fixation costs carbon and is regulated by plant demand. (confidence 0.8)
Fixer litter and root turnover add nitrogen to the soil
PlantsDecomposersNitrogenPlant litter
Evidence (1) · added by Loopa
  • Batterman 2013, Key role of symbiotic dinitrogen fixation in tropical forest secondary succession, Nature, doi:10.1038/nature12525: Fixed N enters the soil N pool through litter. (confidence 0.8)
Soil mineral nitrogen rises
Soil microbesAmmoniumNitrate
Evidence (1) · added by Loopa
  • Batterman 2013, Key role of symbiotic dinitrogen fixation in tropical forest secondary succession, Nature, doi:10.1038/nature12525: Forest N stocks rise during succession with fixers. (confidence 0.8)
High nitrogen availability switches fixation off and fixers lose their edge
RhizobiaLegume rootsNitrogenDinitrogen
Evidence (1) · added by Loopa
  • Batterman 2013, Key role of symbiotic dinitrogen fixation in tropical forest secondary succession, Nature, doi:10.1038/nature12525: Fixation declined as forests aged and N accumulated. (confidence 0.8)
Phosphorus and molybdenum supply can cap fixation
RhizobiaPhosphorusMolybdenum
Evidence (1) · added by Loopa
  • Vitousek & Howarth 1991, Nitrogen limitation on land and in the sea: how can it occur, Biogeochemistry, doi:10.1007/bf00002772: Fixation needs P and Mo, which may limit it before N is satisfied. (confidence 0.7)