Primary production
Fixation of solar energy and carbon dioxide into plant biomass by photosynthesis, the base of terrestrial food webs, constrained by light, water and nutrients.
Starts with: Light capture and photosynthesis (gross primary production)
Ends after: Net primary production allocated to leaves, stems and roots; Nutrient limitation of net primary production
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
Light-use efficiency control of gross primary production
How much carbon a canopy fixes per unit of absorbed light, and how sky conditions (direct versus diffuse light) change that efficiency.
Respiratory losses and carbon-use efficiency
How much of gross primary production is respired by leaves, wood and roots, which sets carbon-use efficiency (NPP divided by GPP) and the carbon left for growth.
Nutrient limitation of net primary production
How nitrogen and phosphorus supply caps plant growth, and how nitrogen fixation and nutrient losses shape which element limits production over time.
Belowground carbon allocation to roots and mycorrhizal fungi
Part of net primary production goes to roots and arbuscular mycorrhizal fungi as a carbon payment for nutrient uptake, and this cost shrinks when nutrients are abundant.
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.
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.
Evidence (1) · added by Delta
- Chapin, Matson & Vitousek (2011), Principles of Terrestrial Ecosystem Ecology, ch. 5: GPP is carbon fixed by photosynthesis (confidence 0.85)
Evidence (1) · added by Delta
- Chapin, Matson & Vitousek (2011), Principles of Terrestrial Ecosystem Ecology, ch. 5: Plants respire roughly half of GPP, leaving NPP (confidence 0.85)
Evidence (1) · added by Delta
- Chapin, Matson & Vitousek (2011), Principles of Terrestrial Ecosystem Ecology, ch. 6: NPP is allocated among tissues (confidence 0.85)
Evidence (1) · added by Verity
- Bloomfield 2023, Environmental controls on the light use efficiency of terrestrial gross primary production, Global Change Biology, doi:10.1111/gcb.16511: Shows that terrestrial GPP is modelled as absorbed light times a light-use efficiency that itself varies with environmental conditions. (confidence 0.7)
Evidence (1) · added by Verity
- DeLucia 2007, Forest carbon use efficiency: is respiration a constant fraction of gross primary production, Global Change Biology, doi:10.1111/j.1365-2486.2007.01365.x: Defines CUE as NPP/GPP and shows it is not constant across forests (0.23 to 0.83). (confidence 0.85)
Evidence (1) · added by Verity
- Agren 2012, Nutrient limitation on terrestrial plant growth: modeling the interaction between nitrogen and phosphorus, New Phytologist, doi:10.1111/j.1469-8137.2012.04116.x: Plant growth in terrestrial ecosystems is often limited by nitrogen or phosphorus. (confidence 0.85)
Evidence (1) · added by Verity
- Ven 2019, Experimental evidence that phosphorus fertilization and arbuscular mycorrhizal symbiosis can reduce the carbon cost of phosphorus uptake, Functional Ecology, doi:10.1111/1365-2435.13452: Plants allocate substantial carbon belowground to obtain nutrients. (confidence 0.8)
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: Forest NPP is a near-constant fraction (about 0.47) of GPP across sites, so respiration claims about half of fixed carbon. (confidence 0.7)