Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Terrestrial nutrient cycling / Progressive nitrogen limitation under rising CO2
Progressive nitrogen limitation under rising CO2
Rising atmospheric CO2 boosts plant growth, which locks more nitrogen in biomass and organic matter and gradually lowers the nitrogen left for growth; plants and fungi can partly compensate by foraging for more soil nitrogen.
Boundary: where this process starts
Starts with: Elevated CO2 raises photosynthesis and net primary production
Boundary: where it ends
Ends after: Growth response to CO2 fades; Fungi and roots forage deeper and mine soil organic nitrogen
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
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.
Elevated CO2 raises photosynthesis and net primary production
Evidence (1) · added by Loopa
- Finzi 2007, Increases in nitrogen uptake rather than nitrogen-use efficiency support higher rates of temperate forest productivity under elevated CO2, PNAS, doi:10.1073/pnas.0706518104: FACE experiments found higher forest productivity under elevated CO2. (confidence 0.8)
More nitrogen is held in long-lived biomass and soil organic matter
Evidence (1) · added by Loopa
- Luo 2004, Progressive nitrogen limitation of ecosystem responses to rising atmospheric carbon dioxide, BioScience, doi:10.1641/0006-3568(2004)054[0731:pnloer]2.0.co;2: Nitrogen sequestered in long-lived pools becomes unavailable for plant growth. (confidence 0.8)
Mineral nitrogen available to plants declines
Evidence (1) · added by Loopa
- Luo 2004, Progressive nitrogen limitation of ecosystem responses to rising atmospheric carbon dioxide, BioScience, doi:10.1641/0006-3568(2004)054[0731:pnloer]2.0.co;2: Declining soil N availability is the mechanism of progressive N limitation. (confidence 0.8)
⑂ How plants meet the extra nitrogen demand
Evidence (1) · added by Loopa
- Terrer 2016, Mycorrhizal association as a primary control of the CO2 fertilization effect, Science, doi:10.1126/science.aaf4610: Mycorrhizal type controls access to soil N under elevated CO2. Shares are an estimate (range roughly 30-50 / 10-20 / 35-55 percent). (confidence 0.4)
Fungi and roots forage deeper and mine soil organic nitrogen
Evidence (1) · added by Loopa
- Finzi 2007, Increases in nitrogen uptake rather than nitrogen-use efficiency support higher rates of temperate forest productivity under elevated CO2, PNAS, doi:10.1073/pnas.0706518104: Increased N uptake rather than higher N use efficiency supported the enhanced productivity at the Duke FACE site. (confidence 0.8)
Extra nitrogen arrives by fixation or deposition
Evidence (1) · added by Loopa
- Fowler 2013, The global nitrogen cycle in the twenty-first century, Phil Trans R Soc B, doi:10.1098/rstb.2013.0165: Reactive nitrogen creation and deposition are significant inputs to terrestrial ecosystems. (confidence 0.8)
Growth response to CO2 fades
Evidence (1) · added by Loopa
- Luo 2004, Progressive nitrogen limitation of ecosystem responses to rising atmospheric carbon dioxide, BioScience, doi:10.1641/0006-3568(2004)054[0731:pnloer]2.0.co;2: Without extra N, ecosystem CO2 response declines over time. (confidence 0.8)
↘ Mycorrhizal carbon-for-nutrient exchange loop
Evidence (1) · added by Loopa
- Terrer 2016, Mycorrhizal association as a primary control of the CO2 fertilization effect, Science, doi:10.1126/science.aaf4610: Mycorrhizal type determines how strongly plants gain nutrients for carbon under elevated CO2. (confidence 0.8)