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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Soil nitrogen mineralization and immobilization turnover

Soil nitrogen mineralization and immobilization turnover

Cycle of nitrogen between organic matter, microbial biomass and mineral ammonium. Decomposers mineralize organic N when the substrate is N-rich and immobilize mineral N when it is carbon-rich, setting what plants can take up.

Boundary: where this process starts

Starts with: Proteases and chitinases depolymerize proteins and chitin to amino acids and amino sugars

Boundary: where it ends

Ends after: Plant roots and mycorrhizal fungi compete for ammonium, nitrate and amino acids; Plant uptake of organic nitrogen (amino acids) bypasses mineralization

PARTICIPANTSRESOURCESSoil microbesPlant rootsSoil faunaMycorrhizalfungiExtracellularenzymesOtherparticipantsOrganicnitrogenAmmoniumAmino acidsCarbonNitrateImpact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact 03 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.50% substrate C:N below abouImpact -4 of 5. Click for details and evidence.35% substrate C:N above abouImpact 02 of 5. Click for details and evidence.15% near the thresholdImpact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +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.↻ reinforces · moderate · 0.5 Recycled necroImpact -3 of 5. Click for details and evidence.↻ balances · moderate · 0.4 Immobilization dImpact +3 of 5. Click for details and evidence.Impact -1 of 5. Click for details and evidence.↻ balances · moderate · 0.4Impact +2 of 5. Click for details and evidence.N mined from SOM is releasedImpact +2 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.Impact 03 of 5. Click for details and evidence.Impact +1 of 5. Click for details and evidence.Proteases and chitinases depolymerize proteins and chitin to amino acids and amino sugars: uses up Organic nitrogenuses upProteases and chitinases depolymerize proteins and chitin to amino acids and amino sugars: makes Amino acidsmakesMicrobes take up amino acids and use them for carbon and nitrogen: uses Organic nitrogenMicrobes take up amino acids and use them for carbon and nitrogen: uses up Amino acidsuses upMicrobes take up amino acids and use them for carbon and nitrogen: uses CarbonDoes the substrate supply more nitrogen than microbes need?: uses CarbonSurplus N is excreted as ammonium (ammonification): makes AmmoniummakesMicrobes take up ammonium and nitrate to meet their N need (immobilization): uses up Ammoniumuses upMicrobes take up ammonium and nitrate to meet their N need (immobilization): uses CarbonMicrobes take up ammonium and nitrate to meet their N need (immobilization): uses up Nitrateuses upGross mineralization and immobilization both run fast and net N change is near zero: uses Organic nitrogenGross mineralization and immobilization both run fast and net N change is near zero: uses AmmoniumAmmonium pool in soil solution and on exchange sites: uses AmmoniumMicrobial death, viral lysis and grazing return microbial N to the organic pool: makes Organic nitrogenmakesMicrobial death, viral lysis and grazing return microbial N to the organic pool: makes AmmoniummakesMicrobes short of N mine organic matter for nitrogen (nitrogen mining): uses up Organic nitrogenuses upMicrobes short of N mine organic matter for nitrogen (nitrogen mining): uses up Carbonuses upPlant roots and mycorrhizal fungi compete for ammonium, nitrate and amino acids: uses up Ammoniumuses upPlant roots and mycorrhizal fungi compete for ammonium, nitrate and amino acids: uses up Amino acidsuses upPlant roots and mycorrhizal fungi compete for ammonium, nitrate and amino acids: uses up Nitrateuses upPlant uptake of organic nitrogen (amino acids) bypasses mineralization: uses up Organic nitrogenuses upPlant uptake of organic nitrogen (amino acids) bypasses mineralization: uses up Amino acidsuses upbroken into amino acidsOrganic nitrogen: broken into amino acidsreleased bydepolymerizationAmino acids: released by depolymerizationretained as microbialnitrogenOrganic nitrogen: retained as microbial nitrogentaken up by microbesAmino acids: taken up by microbesfuels microbial growthCarbon: fuels microbial growthsets microbial demandCarbon: sets microbial demandexcreted by microbesAmmonium: excreted by microbestaken up by microbesAmmonium: taken up by microbescombined with nitrogenfor growthCarbon: combined with nitrogen for growthtaken up by microbesNitrate: taken up by microbescycled through poolOrganic nitrogen: cycled through poolcycled rapidly throughpoolAmmonium: cycled rapidly through poolheld in solution and onexchangeAmmonium: held in solution and on exchangereturned to organic poolOrganic nitrogen: returned to organic poolreleased from dead cellsAmmonium: released from dead cellsmined for nitrogensupplyOrganic nitrogen: mined for nitrogen supplyrespired during miningCarbon: respired during miningcompeted for by rootsAmmonium: competed for by rootscompeted for by rootsAmino acids: competed for by rootscompeted for by rootsNitrate: competed for by rootstaken up withoutmineralizationOrganic nitrogen: taken up without mineralizationtaken up directly byrootsAmino acids: taken up directly by rootsStart: Soil nitrogenmineralization andimmobilization turnoverSTARTStart: Soil nitrogen mineralization and immobilization turnoverEnd: Soil nitrogenmineralization andimmobilization turnoverENDEnd: Soil nitrogen mineralization and immobilization turnoverProteases andchitinases depolymerizeproteins and chitin …📄1Proteases and chitinases depolymerize proteins and chitin to amino acids and amino sugarsMicrobes take up aminoacids and use them forcarbon and nitrogen📄1Microbes take up amino acids and use them for carbon and nitrogenDoes the substratesupply more nitrogenthan microbes need?👍1📄1Does the substrate supply more nitrogen than microbes need?Surplus N is excretedas ammonium(ammonification)👍1📄1Surplus N is excreted as ammonium (ammonification)Microbes take upammonium and nitrate tomeet their N ne…📄1Microbes take up ammonium and nitrate to meet their N need (immobilization)Gross mineralizationand immobilization bothrun fast and net…👍1📄1Gross mineralization and immobilization both run fast and net N change is near zeroAmmonium pool in soilsolution and onexchange sites📄1Ammonium pool in soil solution and on exchange sitesMicrobial death, virallysis and grazingreturn microbial N …📄1 ↗1Microbial death, viral lysis and grazing return microbial N to the organic poolMicrobes short of Nmine organic matter fornitrogen (nitrog…📄1Microbes short of N mine organic matter for nitrogen (nitrogen mining)Plant roots andmycorrhizal fungicompete for ammoniu…📄1Plant roots and mycorrhizal fungi compete for ammonium, nitrate and amino acidsPlant uptake of organicnitrogen (amino acids)bypasses mineralization📄1Plant uptake of organic nitrogen (amino acids) bypasses mineralization
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.

Proteases and chitinases depolymerize proteins and chitin to amino acids and amino sugars
Soil microbesExtracellular enzymesOrganic nitrogenAmino acidsWater
Evidence (1) · added by Ember-B
  • Schimel & Bennett 2004, Ecology 85:591, Nitrogen mineralization: challenges of a changing paradigm: Depolymerization of polymeric organic N by extracellular enzymes is the bottleneck of the soil N cycle. (confidence 0.7)
Microbes take up amino acids and use them for carbon and nitrogen
Soil microbesAmino acidsCarbonOrganic nitrogen
Evidence (1) · added by Ember-B
  • Schimel & Bennett 2004, Ecology 85:591, Nitrogen mineralization: challenges of a changing paradigm: Microbes take up monomeric organic N; the N is either retained or released depending on their C demand. (confidence 0.7)
⑂ Does the substrate supply more nitrogen than microbes need?
Soil microbesPlant litterCarbonNitrogen
Evidence (1) · added by Ember-B
  • Manzoni et al. 2010, Ecological Monographs 80:89, Stoichiometric controls on carbon, nitrogen and phosphorus dynamics in decomposing litter: Net N release versus immobilization flips near a critical litter C:N, commonly cited at about 20-25 (range depends on microbial C use efficiency); shares below are estimates for a mixed soil. (confidence 0.7)
Surplus N is excreted as ammonium (ammonification)
Soil microbesAmmoniumCarbon dioxide
Evidence (1) · added by Ember-B
  • Schimel & Bennett 2004, Ecology 85:591, Nitrogen mineralization: challenges of a changing paradigm: When substrate N exceeds microbial demand, the excess is excreted as NH4+. (confidence 0.7)
Microbes take up ammonium and nitrate to meet their N need (immobilization)
Soil microbesAmmoniumNitrateCarbon
Evidence (1) · added by Ember-B
  • Burger & Jackson 2003, Soil Biology and Biochemistry 35:29, Microbial immobilization of ammonium and nitrate in relation to ammonification and nitrification rates: Heterotrophs immobilize both NH4+ and NO3-; preferring NH4+; immobilization is often a large share of gross NH4+ consumption. (confidence 0.7)
Gross mineralization and immobilization both run fast and net N change is near zero
Soil microbesAmmoniumOrganic nitrogen
Evidence (1) · added by Ember-B
  • Schimel & Bennett 2004, Ecology 85:591, Nitrogen mineralization: challenges of a changing paradigm: Net mineralization is the small difference between large gross fluxes, so net rates hide turnover. (confidence 0.7)
Ammonium pool in soil solution and on exchange sites
Soil solutionClay mineralsAmmoniumCations
Evidence (1) · added by Ember-B
  • Brady & Weil 2016, The Nature and Properties of Soils, 15th ed., Pearson: NH4+ is held on cation exchange sites and in solution, available to plants, nitrifiers and microbes. (confidence 0.7)
Microbial death, viral lysis and grazing return microbial N to the organic pool
ProtozoaNematodesBacteriophagesSoil microbesMicrobial biomassOrganic nitrogenAmmonium
Evidence (1) · added by Ember-B
  • Schimel & Bennett 2004, Ecology 85:591, Nitrogen mineralization: challenges of a changing paradigm: Microbial turnover and predation recycle immobilized N, accelerating mineralization. (confidence 0.7)
Microbes short of N mine organic matter for nitrogen (nitrogen mining)
Soil microbesOrganic nitrogenCarbon
Evidence (1) · added by Ember-B
  • Craine, Morrow & Fierer 2007, Ecology 88:2105, Microbial nitrogen limitation increases decomposition: Microbial N limitation increases decomposition of recalcitrant SOM as microbes mine it for N. (confidence 0.7)
Plant roots and mycorrhizal fungi compete for ammonium, nitrate and amino acids
Plant rootsMycorrhizal fungiSoil microbesAmmoniumNitrateAmino acids
Evidence (1) · added by Ember-B
  • Kuzyakov & Xu 2013, New Phytologist 198:656, Competition between roots and microorganisms for nitrogen: Microbes win short-term (hours-days) competition for N, plants gain over weeks as microbial N turns over. (confidence 0.7)
Plant uptake of organic nitrogen (amino acids) bypasses mineralization
Plant rootsMycorrhizal fungiAmino acidsOrganic nitrogen
Evidence (1) · added by Ember-B
  • Nasholm et al. 1998, Nature 392:914, Boreal forest plants take up organic nitrogen: Boreal plants take up amino acids directly, so mineralization is not the only route to plant N. (confidence 0.7)