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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Terrestrial nutrient cycling / Progressive nitrogen limitation under rising CO2 / Mycorrhizal carbon-for-nutrient exchange loop

Mycorrhizal carbon-for-nutrient exchange loop

Plants pay mycorrhizal fungi with sugars and receive nitrogen and phosphorus in return; extra photosynthate under high CO2 can expand the fungal network and the nutrient supply, up to the point where the fungus itself holds nutrients back.

Boundary: where this process starts

Starts with: Plant sends photosynthate to fungal partners

Boundary: where it ends

Ends after: Fungi hand part of the nitrogen and phosphorus to the plant; Fungi keep nutrients when their own carbon supply or nutrient demand is high, tightening plant nitrogen limitation

PARTICIPANTSRESOURCESMycorrhizalfungiPlantsNitrogenCarbonPhosphorusSugarsSoilImpact +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.↻ reinforces · moderate · 0.3 more nutrient Impact -2 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.↻ balances · weak · 0.15 nutrient withholdinImpact 02 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Plant sends photosynthate to fungal partners: uses up Carbonuses upPlant sends photosynthate to fungal partners: uses up Sugarsuses upHyphae grow and forage a larger soil volume: uses up Nitrogenuses upHyphae grow and forage a larger soil volume: uses up Phosphorususes upHyphae grow and forage a larger soil volume: uses SoilFungi hand part of the nitrogen and phosphorus to the plant: uses NitrogenFungi hand part of the nitrogen and phosphorus to the plant: uses PhosphorusFungi keep nutrients when their own carbon supply or nutrient demand is high, tightening plant nitrogen limitation: uses NitrogenFungi keep nutrients when their own carbon supply or nutrient demand is high, tightening plant nitrogen limitation: uses Carbonsent to fungal partnersCarbon: sent to fungal partnerstransferred as an energysourceSugars: transferred as an energy sourcegathered from distantpatchesNitrogen: gathered from distant patchesgathered from distantpatchesPhosphorus: gathered from distant patchesexplored by growinghyphaeSoil: explored by growing hyphaetransferred to hostrootsNitrogen: transferred to host rootspassed to host rootsPhosphorus: passed to host rootsheld back by fungiNitrogen: held back by fungiretained within fungaltissueCarbon: retained within fungal tissueStart: Mycorrhizalcarbon-for-nutrientexchange loopSTARTStart: Mycorrhizal carbon-for-nutrient exchange loopEnd: Mycorrhizalcarbon-for-nutrientexchange loopENDEnd: Mycorrhizal carbon-for-nutrient exchange loopPlant sendsphotosynthate to fungalpartners📄1Plant sends photosynthate to fungal partnersHyphae grow and foragea larger soil volume📄1Hyphae grow and forage a larger soil volumeFungi hand part of thenitrogen and phosphorusto the plant📄1Fungi hand part of the nitrogen and phosphorus to the plantFungi keep nutrientswhen their own carbonsupply or nutrie…📄1Fungi keep nutrients when their own carbon supply or nutrient demand is high, tightening plant nitrogen limitation
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 sends photosynthate to fungal partners
PlantsMycorrhizal fungiCarbonSugars
Evidence (1) · added by Loopa
  • Terrer 2016, Mycorrhizal association as a primary control of the CO2 fertilization effect, Science, doi:10.1126/science.aaf4610: Fungal partners receive plant carbon. (confidence 0.8)
Hyphae grow and forage a larger soil volume
Mycorrhizal fungiSoilNitrogenPhosphorus
Evidence (1) · added by Loopa
  • Terrer 2016, Mycorrhizal association as a primary control of the CO2 fertilization effect, Science, doi:10.1126/science.aaf4610: Fungal foraging accesses nutrients beyond root depletion zones. (confidence 0.8)
Fungi hand part of the nitrogen and phosphorus to the plant
Mycorrhizal fungiPlantsNitrogenPhosphorus
Evidence (1) · added by Loopa
  • Terrer 2016, Mycorrhizal association as a primary control of the CO2 fertilization effect, Science, doi:10.1126/science.aaf4610: Nutrient transfer supports plant response to CO2. (confidence 0.8)
Fungi keep nutrients when their own carbon supply or nutrient demand is high, tightening plant nitrogen limitation
Mycorrhizal fungiNitrogenCarbon
Evidence (1) · added by Loopa
  • Luo 2004, Progressive nitrogen limitation of ecosystem responses to rising atmospheric carbon dioxide, BioScience, doi:10.1641/0006-3568(2004)054[0731:pnloer]2.0.co;2: Microbial and fungal immobilisation of N can deepen progressive N limitation. (confidence 0.5)