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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Terrestrial nutrient cycling / Litter quality and soil fertility reinforcing loop

Litter quality and soil fertility reinforcing loop

Plants on poor soils shed slow-decaying, low-nitrogen litter that keeps the soil poor, while plants on fertile soils shed fast-decaying litter that keeps it fertile; a reinforcing plant-soil feedback on nutrient supply.

Boundary: where this process starts

Starts with: Nutrient-poor soil favours plants with low-nitrogen, lignin-rich litter

Boundary: where it ends

Ends after: Little mineral nitrogen is released, so plants stay nitrogen-limited; Fertile soil favours fast-growing plants with nitrogen-rich, quickly decomposing litter

PARTICIPANTSRESOURCESPlantsMicrobesDecomposersNitrogenPlant litterAmmoniumCarbonImpact +3 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.litter qualityImpact 03 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.40% net immobilisationImpact +3 of 5. Click for details and evidence.60% net mineralisationImpact -2 of 5. Click for details and evidence.↻ reinforces · moderate · 0.3 low N supply fImpact +2 of 5. Click for details and evidence.↻ reinforces · moderate · 0.3 rich litter spImpact 02 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Nutrient-poor soil favours plants with low-nitrogen, lignin-rich litter: uses NitrogenNutrient-poor soil favours plants with low-nitrogen, lignin-rich litter: uses Plant litterHigh C:N litter decomposes slowly and decomposers immobilise nitrogen: uses up Nitrogenuses upHigh C:N litter decomposes slowly and decomposers immobilise nitrogen: uses Plant litterHigh C:N litter decomposes slowly and decomposers immobilise nitrogen: uses CarbonLitter C:N versus microbial demand sets net nitrogen balance: uses NitrogenLitter C:N versus microbial demand sets net nitrogen balance: uses Plant litterLitter C:N versus microbial demand sets net nitrogen balance: uses AmmoniumLittle mineral nitrogen is released, so plants stay nitrogen-limited: uses NitrogenLittle mineral nitrogen is released, so plants stay nitrogen-limited: uses AmmoniumFertile soil favours fast-growing plants with nitrogen-rich, quickly decomposing litter: uses NitrogenFertile soil favours fast-growing plants with nitrogen-rich, quickly decomposing litter: uses Plant litterscarce, favouring low-NplantsNitrogen: scarce, favouring low-N plantslignin-rich and slowlydecomposingPlant litter: lignin-rich and slowly decomposingimmobilised bydecomposersNitrogen: immobilised by decomposersdecomposes slowly athigh C:NPlant litter: decomposes slowly at high C:Nretained in slow litterCarbon: retained in slow litternet balance set by C:NNitrogen: net balance set by C:NC:N sets microbialdemandPlant litter: C:N sets microbial demandreleased or immobilisedby demandAmmonium: released or immobilised by demandremains limiting toplantsNitrogen: remains limiting to plantslittle released fromlitterAmmonium: little released from littersupports fast-growingplantsNitrogen: supports fast-growing plantsquickly decomposes andreturns nitrogenPlant litter: quickly decomposes and returns nitrogenStart: Litter qualityand soil fertilityreinforcing loopSTARTStart: Litter quality and soil fertility reinforcing loopEnd: Litter quality andsoil fertilityreinforcing loopENDEnd: Litter quality and soil fertility reinforcing loopNutrient-poor soilfavours plants withlow-nitroge…👍1📄1Nutrient-poor soil favours plants with low-nitrogen, lignin-rich litterHigh C:N litterdecomposes slowly anddecomposers immobili…📄1High C:N litter decomposes slowly and decomposers immobilise nitrogenLitter C:N versusmicrobial demand setsnet nitrogen balance👍2📄1Litter C:N versus microbial demand sets net nitrogen balanceLittle mineral nitrogenis released, so plantsstay nitrogen-limited👍1📄1Little mineral nitrogen is released, so plants stay nitrogen-limitedFertile soil favoursfast-growing plantswith nitrogen-ric…👍1📄1Fertile soil favours fast-growing plants with nitrogen-rich, quickly decomposing litter
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.

Nutrient-poor soil favours plants with low-nitrogen, lignin-rich litter
PlantsNitrogenPlant litter
Evidence (1) · added by Loopa
  • Hobbie 1992, Effects of plant species on nutrient cycling, Trends in Ecology & Evolution, doi:10.1016/0169-5347(92)90126-v: Species adapted to infertile sites produce nutrient-poor, slowly decomposing litter. (confidence 0.8)
High C:N litter decomposes slowly and decomposers immobilise nitrogen
MicrobesDecomposersPlant litterNitrogenCarbon
Evidence (1) · added by Loopa
  • Aerts 1997, Climate, leaf litter chemistry and leaf litter decomposition in terrestrial ecosystems, Oikos, doi:10.2307/3546886: Litter nitrogen and lignin content are major controls on litter decomposition rate across biomes. (confidence 0.8)
⑂ Litter C:N versus microbial demand sets net nitrogen balance
MicrobesNitrogenAmmoniumPlant litter
Evidence (1) · added by Loopa
  • Mooshammer 2014, Adjustment of microbial nitrogen use efficiency to carbon:nitrogen imbalances, Nature Communications, doi:10.1038/ncomms4694: Microbes adjust nitrogen use efficiency to resource C:N, retaining N when substrate is N-poor and releasing it when N-rich. Shares are an estimate (range 30-50 percent immobilising). (confidence 0.45)
Little mineral nitrogen is released, so plants stay nitrogen-limited
PlantsMicrobesAmmoniumNitrogen
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: Nitrogen limitation persists because carbon-rich litter drives microbial nitrogen retention. (confidence 0.8)
Fertile soil favours fast-growing plants with nitrogen-rich, quickly decomposing litter
PlantsNitrogenPlant litter
Evidence (1) · added by Loopa
  • Berendse 1994, Litter decomposability a neglected component of plant fitness, Journal of Ecology, doi:10.2307/2261398: Litter decomposability is an overlooked plant trait that feeds back on nutrient availability and species success. (confidence 0.8)