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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Mycorrhizal fungi network / Ectomycorrhizal organic nitrogen mining and the Gadgil effect

Ectomycorrhizal organic nitrogen mining and the Gadgil effect

How ectomycorrhizal fungi pull nitrogen out of soil organic matter with peroxidases and proteases, how that can starve free-living decomposers and slow carbon turnover (the Gadgil effect, a contested idea), and how this shapes soil carbon storage in ectomycorrhizal forests.

Boundary: where this process starts

Starts with: Ectomycorrhizal fungi (Cortinarius, Russula, Suillus) secrete peroxidases and proteases that mine organic nitrogen from soil organic matter

Boundary: where it ends

Ends after: Carbon cost to the host: roughly 10-20% of net primary production goes to ectomycorrhizal fungi (estimate); Evidence for the Gadgil effect is mixed: trenching also changes soil moisture and root input, confounding the result

PARTICIPANTSRESOURCESEctomycorrhizalfungiHost treesSaprotrophicfungiCortinariusResearchersOtherparticipantsNitrogenCarbonSoil organicmatterLitterPeroxidasesImpact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Mined N enters the fungus fiImpact -3 of 5. Click for details and evidence.Mining competes with decompoImpact 02 of 5. Click for details and evidence.Test of the competition effeImpact +3 of 5. Click for details and evidence.Slower turnover raises carboImpact +3 of 5. Click for details and evidence.↻ reinforces · moderate · 0.25 More N lockedImpact -3 of 5. Click for details and evidence.Host pays carbon for NImpact +3 of 5. Click for details and evidence.Nitrogen delivered for carboImpact 01 of 5. Click for details and evidence.Uncertain size of the effectEctomycorrhizal fungi (Cortinarius, Russula, Suillus) secrete peroxidases and proteases that mine organic nitrogen from soil organic matter: makes NitrogenmakesEctomycorrhizal fungi (Cortinarius, Russula, Suillus) secrete peroxidases and proteases that mine organic nitrogen from soil organic matter: uses up Soil organic matteruses upEctomycorrhizal fungi (Cortinarius, Russula, Suillus) secrete peroxidases and proteases that mine organic nitrogen from soil organic matter: uses PeroxidasesFungi retain much of the mined nitrogen and pass only part to the tree when fungal N demand is high, aggravating tree N limitation: uses NitrogenFungi retain much of the mined nitrogen and pass only part to the tree when fungal N demand is high, aggravating tree N limitation: uses CarbonEctomycorrhizal fungi compete with free-living decomposers for N and may slow decomposition (the Gadgil effect): trenching to remove ectomycorrhizal roots raised litter mass loss in a pine plantation: uses NitrogenEctomycorrhizal fungi compete with free-living decomposers for N and may slow decomposition (the Gadgil effect): trenching to remove ectomycorrhizal roots raised litter mass loss in a pine plantation: uses LitterEvidence for the Gadgil effect is mixed: trenching also changes soil moisture and root input, confounding the result: uses LitterEcosystems dominated by ectomycorrhizal and ericoid plants store about 70% more soil carbon per unit nitrogen than arbuscular-dominated ones: uses NitrogenEcosystems dominated by ectomycorrhizal and ericoid plants store about 70% more soil carbon per unit nitrogen than arbuscular-dominated ones: uses CarbonEcosystems dominated by ectomycorrhizal and ericoid plants store about 70% more soil carbon per unit nitrogen than arbuscular-dominated ones: makes Soil organic mattermakesCarbon cost to the host: roughly 10-20% of net primary production goes to ectomycorrhizal fungi (estimate): uses up Carbonuses upreleased from organicmatterNitrogen: released from organic mattermined by peroxidases andproteasesSoil organic matter: mined by peroxidases and proteasessecreted to break downorganicsPeroxidases: secreted to break down organicsretained, only partlypassed to treeNitrogen: retained, only partly passed to treetransferred to fungalpartnerCarbon: transferred to fungal partnercompeted for by freedecomposersNitrogen: competed for by free decomposersmass loss slowed bycompetitionLitter: mass loss slowed by competitiondecay confounded by rootinputLitter: decay confounded by root inputretained alongsidestored carbonNitrogen: retained alongside stored carbonstored in soil ingreater amountsCarbon: stored in soil in greater amountsstored per unit nitrogenSoil organic matter: stored per unit nitrogendiverted toectomycorrhizal fungiCarbon: diverted to ectomycorrhizal fungiStart: Ectomycorrhizalorganic nitrogen miningand the Gadgil effectSTARTStart: Ectomycorrhizal organic nitrogen mining and the Gadgil effectEnd: Ectomycorrhizalorganic nitrogen miningand the Gadgil effectENDEnd: Ectomycorrhizal organic nitrogen mining and the Gadgil effectEctomycorrhizal fungi(Cortinarius, Russula,Suillus) secre…📄1Ectomycorrhizal fungi (Cortinarius, Russula, Suillus) secrete peroxidases and proteases that mine organic nitrogen from soil organic matterFungi retain much ofthe mined nitrogen andpass only part to t…📄1Fungi retain much of the mined nitrogen and pass only part to the tree when fungal N demand is high, aggravating tree N limitationEctomycorrhizal fungicompete withfree-living decompose…📄1Ectomycorrhizal fungi compete with free-living decomposers for N and may slow decomposition (the Gadgil effect): trenching to remove ectomycorrhizal roots raised litter mass loss in a pine plantationEvidence for the Gadgileffect is mixed:trenching also chang…📄1Evidence for the Gadgil effect is mixed: trenching also changes soil moisture and root input, confounding the resultEcosystems dominated byectomycorrhizal andericoid plants sto…📄1Ecosystems dominated by ectomycorrhizal and ericoid plants store about 70% more soil carbon per unit nitrogen than arbuscular-dominated onesCarbon cost to thehost: roughly 10-20% ofnet primary producti…📄1Carbon cost to the host: roughly 10-20% of net primary production goes to ectomycorrhizal fungi (estimate)
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
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Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
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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
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Boundary
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Subprocess
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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

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Ectomycorrhizal fungi (Cortinarius, Russula, Suillus) secrete peroxidases and proteases that mine organic nitrogen from soil organic matter
Ectomycorrhizal fungiCortinariusSoil organic matterNitrogenPeroxidases
Evidence (1) · added by Ember
  • Bodeker et al. 2014, New Phytologist 203:245, Ectomycorrhizal Cortinarius species participate in enzymatic oxidation of humus in northern forest ecosystems: Cortinarius species expressed Mn peroxidase genes and oxidized humus in boreal forest soil. (confidence 0.85)
Fungi retain much of the mined nitrogen and pass only part to the tree when fungal N demand is high, aggravating tree N limitation
Ectomycorrhizal fungiHost treesNitrogenCarbon
Evidence (1) · added by Ember
  • Nasholm, Hogberg, Franklin, Metcalfe, Gruffman, Ishida, Hogberg, Wallander 2013, New Phytologist 198:214, Are ectomycorrhizal fungi alleviating or aggravating nitrogen limitation of tree growth in boreal forests?: Fungal N retention can lower N delivered to the host at low soil N. (confidence 0.8)
Ectomycorrhizal fungi compete with free-living decomposers for N and may slow decomposition (the Gadgil effect): trenching to remove ectomycorrhizal roots raised litter mass loss in a pine plantation
Ectomycorrhizal fungiSaprotrophic fungiNitrogenLitter
Evidence (1) · added by Ember
  • Gadgil & Gadgil 1971, Nature 233:133, Mycorrhiza and litter decomposition: Litter decomposed faster in trenched plots without mycorrhizal roots than in untrenched plots. (confidence 0.85)
Evidence for the Gadgil effect is mixed: trenching also changes soil moisture and root input, confounding the result
Ectomycorrhizal fungiResearchersWaterLitter
Evidence (1) · added by Ember
  • Fernandez & Kennedy 2016, New Phytologist 209:1382, Revisiting the Gadgil effect: do interguild fungal interactions control carbon cycling in forest soils?: Reviewed trenching studies; results varied and moisture and other confounders were common. (confidence 0.85)
Ecosystems dominated by ectomycorrhizal and ericoid plants store about 70% more soil carbon per unit nitrogen than arbuscular-dominated ones
Ectomycorrhizal forestsEricoid heathlandsSoil organic matterCarbonNitrogen
Evidence (1) · added by Ember
  • Averill, Turner & Finzi 2014, Nature 505:543, Mycorrhiza-mediated competition between plants and decomposers drives soil carbon storage: Soil C per unit N was about 70% higher in ectomycorrhizal and ericoid than in arbuscular mycorrhizal systems in a global dataset. (confidence 0.7)
Carbon cost to the host: roughly 10-20% of net primary production goes to ectomycorrhizal fungi (estimate)
Host treesEctomycorrhizal fungiCarbonSugars
Evidence (1) · added by Ember
  • Hobbie 2006, Ecology 87:563, Carbon allocation to ectomycorrhizal fungi correlates with belowground allocation in culture studies: Isotope and allocation estimates place ectomycorrhizal carbon use at roughly 10-20% of NPP, with wide uncertainty. (confidence 0.5)