Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Soil gas exchange and redox / Soil respiration: temperature and moisture control and climate feedback
Soil respiration: temperature and moisture control and climate feedback
Soil CO2 efflux is about 98 Pg C per year and responds to temperature (Q10 about 1.5 to 3) and to water-filled pore space (optimum near 60 percent). Warming increases CO2 release and creates a positive climate feedback, partly limited by substrate depletion.
Boundary: where this process starts
Starts with: Soil CO2 efflux reaches about 98 Pg C per year globally, far above fossil emissions of about 9 Pg C
Boundary: where it ends
Ends after: Warming-driven CO2 release adds to atmospheric CO2; models suggest tens of Pg C lost by 2050 (central estimate about 55 Pg C with similar uncertainty); Rewetting dry soil causes a CO2 and mineral N pulse within hours (Birch effect) from released osmolytes and exposed organic matter
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.
Soil CO2 efflux reaches about 98 Pg C per year globally, far above fossil emissions of about 9 Pg C
Evidence (1) · added by Fern
- Bond-Lamberty & Thomson (2010), Nature 464:579-582: Global soil respiration was estimated at about 98 Pg C in 2008. (confidence 0.8)
Warming speeds enzyme and respiration rates, with Q10 typically 1.5 to 3 and higher at low temperature
Evidence (1) · added by Fern
- Lloyd & Taylor (1994), On the temperature dependence of soil respiration, Functional Ecology 8:315-323: Soil respiration follows an Arrhenius-type curve in which apparent Q10 declines as temperature rises. (confidence 0.8)
Moisture optimum near 60 percent water-filled pore space: drier soil limits substrate diffusion, wetter soil limits oxygen
Evidence (1) · added by Fern
- Linn & Doran (1984), Effect of water-filled pore space on carbon dioxide and nitrous oxide production in tilled and nontilled soils, Soil Science Society of America Journal 48:1267-1272: Aerobic microbial activity peaked at about 60 percent water-filled pore space. (confidence 0.85)
Rewetting dry soil causes a CO2 and mineral N pulse within hours (Birch effect) from released osmolytes and exposed organic matter
Evidence (1) · added by Fern
- Birch (1958), The effect of soil drying on humus decomposition and nitrogen availability, Plant and Soil 10:9-31: Drying and rewetting stimulated a flush of mineralisation compared with continuously moist soil. (confidence 0.8)
Warming-driven CO2 release adds to atmospheric CO2; models suggest tens of Pg C lost by 2050 (central estimate about 55 Pg C with similar uncertainty)
Evidence (1) · added by Fern
- Crowther et al. (2016), Quantifying global soil carbon losses in response to warming, Nature 540:104-108: A warming of about 1 degree was estimated to cause a loss of about 55 Pg C by 2050, with an uncertainty of similar magnitude. (confidence 0.6)
Labile carbon is used up, so respiration per unit soil falls after several years of warming (Harvard Forest soil warming, 5 degrees)
Evidence (1) · added by Fern
- Melillo et al. (2002), Soil warming and carbon-cycle feedbacks to the climate system, Science 298:2173-2176: Extra soil CO2 release under warming lasted about 6 years and then declined as labile carbon was depleted. (confidence 0.8)