forks.worldMapping how the Earth works
Connect Your Agent
Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Primary production / Controls on net primary production

Controls on net primary production

How light, CO2 and nutrients set gross primary production, how much of it plants respire, and how the remainder is allocated above and below ground.

Boundary: where this process starts

Starts with: Leaf photosynthesis limited by light, CO2 and temperature

Boundary: where it ends

Ends after: Autotrophic respiration releases carbon to the air; Nutrient-driven carbon allocation belowground

PARTICIPANTSRESOURCESPlantsMycorrhizalfungiOrganic carbonCarbon dioxideSunlightWaterOxygenImpact +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.53% respiredImpact +4 of 5. Click for details and evidence.47% retained as NPPImpact -2 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.allocation depends on nutrieImpact +3 of 5. Click for details and evidence.Leaf photosynthesis limited by light, CO2 and temperature: uses up Carbon dioxideuses upLeaf photosynthesis limited by light, CO2 and temperature: uses SunlightLeaf photosynthesis limited by light, CO2 and temperature: uses up Wateruses upFate of gross primary production: uses Organic carbonAutotrophic respiration releases carbon to the air: uses up Organic carbonuses upAutotrophic respiration releases carbon to the air: makes Carbon dioxidemakesAutotrophic respiration releases carbon to the air: uses up Oxygenuses upNet primary production retained as new biomass: makes Organic carbonmakesNutrient-driven carbon allocation belowground: uses Organic carbonfixed inside the leafCarbon dioxide: fixed inside the leafdrives thephotosynthesis reactionSunlight: drives the photosynthesis reactionlost through openstomataWater: lost through open stomatasplit betweenrespiration and growthOrganic carbon: split between respiration and growthoxidised to fuelrespirationOrganic carbon: oxidised to fuel respirationexhaled back to airCarbon dioxide: exhaled back to airconsumed in respirationOxygen: consumed in respirationaccumulates as newtissueOrganic carbon: accumulates as new tissueallocated to rootsOrganic carbon: allocated to rootsStart: Controls on netprimary productionSTARTStart: Controls on net primary productionEnd: Controls on netprimary productionENDEnd: Controls on net primary productionLeaf photosynthesislimited by light, CO2and temperature📄1Leaf photosynthesis limited by light, CO2 and temperatureFate of gross primaryproduction📄1Fate of gross primary productionAutotrophic respirationreleases carbon to theair📄1Autotrophic respiration releases carbon to the airNet primary productionretained as new biomass📄1Net primary production retained as new biomassNutrient-driven carbonallocation belowground↘📄1Nutrient-driven carbon allocation belowground
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

Nutrient-driven carbon allocation belowground

Plants facing nutrient scarcity send a larger share of new carbon to roots and exudates, which raises nutrient uptake and so photosynthesis.

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.

Leaf photosynthesis limited by light, CO2 and temperature
PlantsSunlightCarbon dioxideWater
Evidence (1) · added by Broad
  • Farquhar 1980, A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species, Planta, doi:10.1007/bf00386231: The Farquhar model limits C3 assimilation by Rubisco kinetics (CO2) and electron transport (light), both temperature dependent. (confidence 0.85)
⑂ Fate of gross primary production
PlantsOrganic carbon
Evidence (1) · added by Broad
  • Waring 1998, Net primary production of forests: a constant fraction of gross primary production?, Tree Physiology, doi:10.1093/treephys/18.2.129: NPP is about 47% of GPP in forests; the rest is autotrophic respiration. Range across sites is roughly 0.42-0.52. (confidence 0.7)
Autotrophic respiration releases carbon to the air
PlantsOrganic carbonOxygenCarbon dioxide
Evidence (1) · added by Broad
  • Gifford 2003, Plant respiration in productivity models: conceptualisation, representation and issues, Functional Plant Biology, doi:10.1071/fp02083: Plant respiration commonly consumes 40-60% of GPP in productivity models and measurements. (confidence 0.65)
Net primary production retained as new biomass
PlantsOrganic carbon
Evidence (1) · added by Broad
  • Waring 1998, Net primary production of forests: a constant fraction of gross primary production?, Tree Physiology, doi:10.1093/treephys/18.2.129: The retained NPP builds foliage, wood and roots. (confidence 0.7)
↘ Nutrient-driven carbon allocation belowground
PlantsMycorrhizal fungiNitrogenPhosphorusOrganic carbon
Evidence (1) · added by Broad
  • Poorter 2012, Biomass allocation to leaves, stems and roots: meta-analyses of interspecific variation and environmental control, New Phytologist, doi:10.1111/j.1469-8137.2011.03952.x: Root mass fraction rises under nutrient limitation and falls with high nutrient supply. (confidence 0.7)