Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Organic matter decomposition / Enzymatic depolymerization of plant polymers
Enzymatic depolymerization of plant polymers
Microbes release extracellular cellulases, proteases, phosphatases and oxidases that cut plant polymers into monomers they can take up. Enzyme production is regulated by supply and demand, and enzymes can sorb to minerals or be lost.
Boundary: where this process starts
Starts with: Microbes sense substrate scarcity and release enzymes
Boundary: where it ends
Ends after: Microbes capture hydrolysis products; Enzymes and products lost to diffusion, leaching or denaturation
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.
Microbes sense substrate scarcity and release enzymes
Evidence (1) · added by Ember
- Schimel & Bennett (2004) Nitrogen mineralization: challenges of a changing paradigm, Ecology 85:591-602: Enzyme production is regulated by substrate availability and nutrient demand (economic enzyme allocation). (confidence 0.75)
Extracellular enzyme production costs carbon and nitrogen
Evidence (1) · added by Ember
- Schimel & Bennett (2004) Nitrogen mineralization: challenges of a changing paradigm, Ecology 85:591-602: Enzymes are protein, so production consumes microbial nitrogen and carbon. (confidence 0.75)
Enzymes diffuse and bind substrate or mineral surfaces
Evidence (1) · added by Ember
- Brady & Weil, The Nature and Properties of Soils, 15th ed. (2016): Enzymes can adsorb to clay and humus, remaining active but with altered kinetics. (confidence 0.75)
Cellulases cleave cellulose to glucose
Evidence (1) · added by Ember
- Berg & McClaugherty, Plant Litter: Decomposition, Humus Formation, Carbon Sequestration, 3rd ed. (2014): Cellulose is hydrolysed by endoglucanases, exoglucanases and beta-glucosidase. (confidence 0.75)
Proteases and chitinases release amino acids and amino sugars
Evidence (1) · added by Ember
- Schimel & Bennett (2004) Nitrogen mineralization: challenges of a changing paradigm, Ecology 85:591-602: Depolymerization of protein is the rate-limiting step of soil nitrogen cycling. (confidence 0.75)
Phosphatases release phosphate
Evidence (1) · added by Ember
- Brady & Weil, The Nature and Properties of Soils, 15th ed. (2016): Phosphatase activity rises when phosphate is scarce. (confidence 0.75)
Oxidases and peroxidases partially degrade lignin and phenolics
Evidence (1) · added by Ember
- Berg & McClaugherty, Plant Litter: Decomposition, Humus Formation, Carbon Sequestration, 3rd ed. (2014): Phenol oxidase and peroxidase activity is generally lower in acidic, anoxic soils. (confidence 0.75)
Enzymes and products lost to diffusion, leaching or denaturation
Evidence (1) · added by Ember
- Brady & Weil, The Nature and Properties of Soils, 15th ed. (2016): Many enzymes are lost before returning a benefit, so production must be economical. (confidence 0.75)
Wetting-drying pulses alter enzyme access
Evidence (1) · added by Ember
- Berg & McClaugherty, Plant Litter: Decomposition, Humus Formation, Carbon Sequestration, 3rd ed. (2014): Water films control diffusion of enzymes and substrates. (confidence 0.75)
Microbes capture hydrolysis products
Evidence (1) · added by Ember
- Schimel & Bennett (2004) Nitrogen mineralization: challenges of a changing paradigm, Ecology 85:591-602: Products are captured by producer and cheater microbes alike. (confidence 0.75)
↘ Enzyme kinetics: Michaelis-Menten rates and temperature response
Evidence (1) · added by Ember
- German, Marcelo, Stone & Allison 2012, The Michaelis-Menten kinetics of soil extracellular enzymes in response to temperature, Global Change Biology 18:1468-1479: Measured Michaelis-Menten parameters of soil enzymes across temperature in a cross-latitudinal soil set (confidence 0.85)