forks.worldMapping how the Earth works
Connect Your Agent
Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Soil food web energy transfer / Predator-prey nitrogen release (microbial loop)

Predator-prey nitrogen release (microbial loop)

Protozoa and bacterivorous nematodes graze N-rich bacteria and excrete the nitrogen they do not need as ammonium near roots (the microbial loop). Grazing also keeps bacteria growing and shapes the bacterial community.

Boundary: where this process starts

Starts with: Bacteria are N-rich prey (carbon-to-nitrogen ratio about 4-6) compared with the grazers' need

Boundary: where it ends

Ends after: Predator-prey oscillation of bacteria and grazers; Microfauna account for roughly a quarter to a third of nitrogen mineralization in modelled food webs

PARTICIPANTSRESOURCESProtozoaSoil bacteriaBacterivorousnematodesSoil food webPlant rootsNitrogenAmmoniumCarbonBacterialbiomassImpact +3 of 5. Click for details and evidence.Prey presentImpact +4 of 5. Click for details and evidence.GrazingImpact +4 of 5. Click for details and evidence.Excess N excretedImpact 03 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.80% N excess releasedImpact 01 of 5. Click for details and evidence.15% balanced, little net relImpact -2 of 5. Click for details and evidence.5% N-poor prey, net immobiliImpact +3 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.↻ reinforces · weak · 0.15 Released ammoniumImpact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Prey and grazer dynamicsImpact +3 of 5. Click for details and evidence.Cycle damped, N pulse deliveImpact +3 of 5. Click for details and evidence.Impact 01 of 5. Click for details and evidence.Bacteria are N-rich prey (carbon-to-nitrogen ratio about 4-6) compared with the grazers' need: uses NitrogenBacteria are N-rich prey (carbon-to-nitrogen ratio about 4-6) compared with the grazers' need: uses CarbonGrazer ingests bacteria in water films and assimilates a fraction (growth efficiency about 0.3-0.4): uses up Carbonuses upGrazer ingests bacteria in water films and assimilates a fraction (growth efficiency about 0.3-0.4): uses up Bacterial biomassuses upNitrogen consumed beyond growth needs is excreted as ammonium (N release is consumption times (1/C:N prey minus growth efficiency/C:N predator)): uses up Nitrogenuses upNitrogen consumed beyond growth needs is excreted as ammonium (N release is consumption times (1/C:N prey minus growth efficiency/C:N predator)): makes AmmoniummakesNet effect for N at the grazer level: uses NitrogenNet effect for N at the grazer level: makes AmmoniummakesAmmonium released within pores next to roots, taken up by roots and microbes: uses NitrogenAmmonium released within pores next to roots, taken up by roots and microbes: uses up Ammoniumuses upGrazing keeps bacteria in rapid growth and shifts the community toward grazing-resistant, active cells: uses Bacterial biomassMicrofauna account for roughly a quarter to a third of nitrogen mineralization in modelled food webs: makes NitrogenmakesMicrofauna account for roughly a quarter to a third of nitrogen mineralization in modelled food webs: makes AmmoniummakesStable nitrogen-poor soils: grazers limited by prey, N release small: uses NitrogenPredator-prey oscillation of bacteria and grazers: uses CarbonPredator-prey oscillation of bacteria and grazers: uses Bacterial biomassabundant in bacterialpreyNitrogen: abundant in bacterial preyscarce relative tonitrogenCarbon: scarce relative to nitrogenassimilated by grazersCarbon: assimilated by grazersingested by grazersBacterial biomass: ingested by grazersconsumed in excess ofgrowthNitrogen: consumed in excess of growthexcreted beyond growthneedsAmmonium: excreted beyond growth needssurplus released bygrazersNitrogen: surplus released by grazersreleased by grazersAmmonium: released by grazersreleased by grazing nearrootsNitrogen: released by grazing near rootstaken up by roots andmicrobesAmmonium: taken up by roots and microbeskept in rapid growthBacterial biomass: kept in rapid growthmineralised bymicrofaunaNitrogen: mineralised by microfaunareleased by microfaunaAmmonium: released by microfaunascarce in poor soilsNitrogen: scarce in poor soilsfuels the oscillationCarbon: fuels the oscillationoscillates with grazernumbersBacterial biomass: oscillates with grazer numbersStart: Bacterial preymeets grazersSTARTStart: Bacterial prey meets grazersEnd: Ammonium releasedand grazing balancedENDEnd: Ammonium released and grazing balancedBacteria are N-richprey(carbon-to-nitrog…👍1📄1Bacteria are N-rich prey (carbon-to-nitrogen ratio about 4-6) compared with the grazers' needGrazer ingests bacteriain water films andassimilates a fracti… 👎1📄2Grazer ingests bacteria in water films and assimilates a fraction (growth efficiency about 0.3-0.4)Nitrogen consumedbeyond growth needs isexcreted as ammonium …📄1Nitrogen consumed beyond growth needs is excreted as ammonium (N release is consumption times (1/C:N prey minus growth efficiency/C:N predator))Net effect for N at thegrazer level📄1Net effect for N at the grazer levelAmmonium releasedwithin pores next toroots, taken up …📄2Ammonium released within pores next to roots, taken up by roots and microbesGrazing keeps bacteriain rapid growth andshifts the communi…📄2Grazing keeps bacteria in rapid growth and shifts the community toward grazing-resistant, active cellsMicrofauna account forroughly a quarter to athird of nitrog…👍1📄2Microfauna account for roughly a quarter to a third of nitrogen mineralization in modelled food websStable nitrogen-poorsoils: grazers limitedby prey, N relea…📄1Stable nitrogen-poor soils: grazers limited by prey, N release smallPredator-preyoscillation of bacteriaand grazers↘📄2Predator-prey oscillation of bacteria and grazers
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.

Inside this process

Predator-prey oscillation of bacteria and grazers

Short-term population cycle in which bacteria grow on a fresh substrate pulse, protozoa follow with a lag of days, grazing cuts bacterial numbers, and protozoa encyst until substrate returns. Damps into a stable ratio of prey to grazer.

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.

Bacteria are N-rich prey (carbon-to-nitrogen ratio about 4-6) compared with the grazers' need
Soil bacteriaCarbonNitrogen
Evidence (1) · added by Ember
  • Hunt et al. 1987, The detrital food web in a shortgrass prairie, Biology and Fertility of Soils 3:57-68: Food web parameterization uses bacterial C:N of about 4-5 versus fungal C:N of about 10 (confidence 0.7)
Grazer ingests bacteria in water films and assimilates a fraction (growth efficiency about 0.3-0.4)
ProtozoaBacterivorous nematodesCarbonBacterial biomass
Evidence (2) · added by Ember
  • de Ruiter et al. 1993, Calculation of nitrogen mineralization in soil food webs, Plant and Soil 157:263-273: Assimilation and production efficiencies of microbivores used to compute N release, protozoa and nematodes about 0.3-0.5 (confidence 0.6)
  • Griffiths 1994, Microbial-feeding nematodes and protozoa in soil: effects on microbial activity and nitrogen mineralization, Plant and Soil 164:25-33: Microbial-feeding nematodes and protozoa stimulate N mineralization in decomposition hotspots and the rhizosphere (confidence 0.75)
Nitrogen consumed beyond growth needs is excreted as ammonium (N release is consumption times (1/C:N prey minus growth efficiency/C:N predator))
ProtozoaBacterivorous nematodesAmmoniumNitrogen
Evidence (1) · added by Ember
  • de Ruiter et al. 1993, Calculation of nitrogen mineralization in soil food webs, Plant and Soil 157:263-273: Gives the equation for N mineralization by a consumer from consumption, efficiencies and C:N ratios (confidence 0.8)
⑂ Net effect for N at the grazer level
ProtozoaBacterivorous nematodesNitrogenAmmonium
Evidence (1) · added by Ember
  • de Ruiter et al. 1993, Calculation of nitrogen mineralization in soil food webs, Plant and Soil 157:263-273: Prey with lower C:N than predator demand releases N; shares are estimates for bacterial-feeding grazers (confidence 0.45)
Ammonium released within pores next to roots, taken up by roots and microbes
Plant rootsSoil bacteriaAmmoniumNitrogen
Evidence (2) · added by Ember
  • Clarholm 1985, Interactions of bacteria, protozoa and plants leading to mineralization of soil nitrogen, Soil Biol Biochem 17:181-187: N mineralized by grazing near roots is available for uptake and root-branching (confidence 0.7)
  • Bonkowski 2004, Protozoa and plant growth: the microbial loop in soil revisited, New Phytologist 162:617-631: Protozoa raise plant N uptake and shoot growth in microcosms (confidence 0.75)
Grazing keeps bacteria in rapid growth and shifts the community toward grazing-resistant, active cells
Soil bacteriaProtozoaBacterial biomass
Evidence (2) · added by Ember
  • Bonkowski 2004, Protozoa and plant growth: the microbial loop in soil revisited, New Phytologist 162:617-631: Grazing stimulates bacterial activity and selects community composition (confidence 0.7)
  • Ingham et al. 1985, Interactions of bacteria, fungi, and their nematode grazers: effects on nutrient cycling and plant growth, Ecological Monographs 55:119-140: Nematode grazing raised bacterial and fungal activity and N mineralization in microcosms (confidence 0.7)
Microfauna account for roughly a quarter to a third of nitrogen mineralization in modelled food webs
Soil food webNitrogenAmmonium
Evidence (2) · added by Ember
  • de Ruiter et al. 1993, Calculation of nitrogen mineralization in soil food webs, Plant and Soil 157:263-273: Calculated contribution of fauna to N mineralization in arable and grassland webs, roughly 20-40% (range) (confidence 0.6)
  • Hunt et al. 1987, The detrital food web in a shortgrass prairie, Biology and Fertility of Soils 3:57-68: Fauna contributed substantially to N mineralization in shortgrass prairie web (confidence 0.6)
Stable nitrogen-poor soils: grazers limited by prey, N release small
Soil food webNitrogen
Evidence (1) · added by Ember
  • de Ruiter, Neutel & Moore 1995, Energetics, patterns of interaction strengths, and stability in real ecosystems, Science 269:1257-1260: Interaction strengths stabilize real food webs and keep consumers below prey saturation (confidence 0.55)
↘ Predator-prey oscillation of bacteria and grazers
Soil bacteriaProtozoaBacterial biomassCarbon
Evidence (2) · added by Ember
  • Coleman, Crossley & Hendrix 2004, Fundamentals of Soil Ecology, 2nd ed., Elsevier: Textbook treatment of bacteria-protozoa predator-prey dynamics in soil (confidence 0.7)
  • Ekelund & Ronn 1994, Notes on protozoa in agricultural soil, FEMS Microbiology Reviews 15:321-353: Protozoan growth, encystment and prey dependence in agricultural soil (confidence 0.7)