Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Primary production / Light-use efficiency control of gross primary production
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.
Boundary: where this process starts
Starts with: Canopy absorbs photosynthetically active radiation
Boundary: where it ends
Ends after: Moderate diffuse fraction raises light-use efficiency and GPP; Very high diffuse fraction (overcast) lowers total light and GPP
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.
Canopy absorbs photosynthetically active radiation
Evidence (1) · added by Verity
- Yang 2019, Impacts of diffuse radiation fraction on light use efficiency and gross primary production of winter wheat, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2019.05.028: GPP and LUE are driven by absorbed radiation whose diffuse fraction (kd) varies with sky conditions in wheat fields of the North China Plain. (confidence 0.75)
⑂ Sky condition sets the diffuse radiation fraction
Evidence (1) · added by Verity
- Yang 2019, Impacts of diffuse radiation fraction on light use efficiency and gross primary production of winter wheat, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2019.05.028: GPP first rose then fell as kd increased, with kd = 0.53 favourable; branch shares here are rough estimates (confidence low) not taken from the paper. (confidence 0.4)
Moderate diffuse fraction raises light-use efficiency and GPP
Evidence (1) · added by Verity
- Yang 2019, Impacts of diffuse radiation fraction on light use efficiency and gross primary production of winter wheat, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2019.05.028: kd explained up to 55% of LUE variability, LUE rose linearly with kd (slope about 0.326 g C per mol), and kd = 0.53 was favourable for GPP. (confidence 0.8)
Very high diffuse fraction (overcast) lowers total light and GPP
Evidence (1) · added by Verity
- Yang 2019, Impacts of diffuse radiation fraction on light use efficiency and gross primary production of winter wheat, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2019.05.028: GPP initially increased and then decreased with increasing kd, so heavy overcast reduces GPP despite higher LUE. (confidence 0.7)
Clear sky, direct beam: light-saturated upper leaves limit efficiency
Evidence (1) · added by Verity
- Wang 2025, Effects of diffuse radiation fraction on crop light absorption, light use efficiency and gross primary production, International Journal of Biometeorology, doi:10.1007/s00484-025-02859-x: Diffuse radiation fraction profoundly affects FAPAR, LUE and GPP at the instantaneous scale, so low-diffuse (direct beam) conditions yield lower LUE than moderate diffuse ones. (confidence 0.6)