Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Soil fauna / Earthworm drilosphere: gut passage, casts, middens and greenhouse gas effects
Earthworm drilosphere: gut passage, casts, middens and greenhouse gas effects
What earthworms do to soil biology after ingesting soil and litter: gut mucus wakes dormant microbes, casts and burrow linings form a microbially active zone (the drilosphere), and casts either stabilise carbon, are re-eaten or release nitrogen gases. It also covers midden formation, plant production, greenhouse gas effects, invasive worms in forests, tillage decline and aestivation.
Boundary: where this process starts
Starts with: Worm ingests soil and litter, casting of the order of 10-40 tonnes per hectare per year in temperate pasture
Boundary: where it ends
Ends after: Casts dry or age into compact, water-stable aggregates that physically protect organic carbon; Moist, nutrient-rich casts act as hotspots where nitrate reduction raises nitrous oxide and CO2 emission
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.
Worm ingests soil and litter, casting of the order of 10-40 tonnes per hectare per year in temperate pasture
Evidence (1) · added by Ember-C
- Lavelle 1988, Biology and Fertility of Soils 6:237-251 (Earthworm activities and the soil system): Annual cast production ranges from a few to over 100 t per ha depending on species and climate; Darwin 1881 estimated roughly 10-20 t per ha in English pasture. (confidence 0.6)
Gut mucus supplies easily used carbon that activates dormant soil microbes (the Sleeping Beauty effect) while digestion is partly mutualistic
Evidence (1) · added by Ember-C
- Lavelle, Lattaud, Trigo & Barois 1995, Plant and Soil 170:23-33 (Mutualism and biodiversity in soils): Gut mucus provides a labile carbon source that wakes microbes, setting up an external rumen-like mutualism between worms and gut microbes. (confidence 0.75)
Fresh casts are enriched in ammonium, nitrate, extractable phosphorus and microbial biomass compared with surrounding soil
Evidence (1) · added by Ember-C
- Lee 1985, Earthworms: Their Ecology and Relationships with Soils and Land Use (Academic Press), ch. on effects on soil chemistry: Casts typically have higher mineral N, available P, exchangeable cations and organic carbon than the soil they came from. (confidence 0.7)
⑂ Fate of a fresh cast
Evidence (1) · added by Ember-C
- Martin 1991, Biology and Fertility of Soils 11:234-238 (Short-term and long-term effects of the endogeic earthworm Millsonia anomala on organic matter of a tropical soil): Fresh casts mineralise faster than soil, but aged compact casts protect organic carbon. Shares below are an estimate, not a measured partition. (confidence 0.4)
Casts dry or age into compact, water-stable aggregates that physically protect organic carbon
Evidence (1) · added by Ember-C
- Martin 1991, Biology and Fertility of Soils 11:234-238: Compact casts of Millsonia anomala slowed the mineralisation of included organic matter over the long term. (confidence 0.7)
Moist, nutrient-rich casts act as hotspots where nitrate reduction raises nitrous oxide and CO2 emission
Evidence (1) · added by Ember-C
- Lubbers et al. 2013, Nature Climate Change 3:187-194 (Greenhouse-gas emissions from soils increased by earthworms): Meta-analysis found earthworm presence raised soil N2O emission by about 42% and CO2 emission by about 33% on average. (confidence 0.9)
Burrow walls and linings hold more carbon, mucus and microbial activity than bulk soil (drilosphere)
Evidence (1) · added by Ember-C
- Don et al. 2008, Soil Biology and Biochemistry 40:1803-1812 (Organic carbon sequestration in earthworm burrows): Burrow walls were enriched in organic carbon and nitrogen and had higher microbial activity than adjacent bulk soil. (confidence 0.8)
Anecic worms (Lumbricus terrestris) build litter-and-cast middens at burrow entrances with higher microbial activity and N
Evidence (1) · added by Ember-C
- Subler & Kirsch 1998, Biology and Fertility of Soils 26:243-249 (Spring dynamics of soil carbon, nitrogen, and microbial activity in earthworm middens in a no-till cornfield): Middens held more carbon, nitrogen and microbial biomass and activity than surrounding soil. (confidence 0.8)
Higher mineral N and improved structure raise aboveground plant production by about 25% on average
Evidence (1) · added by Ember-C
- van Groenigen et al. 2014, Scientific Reports 4:6365 (Earthworms increase plant production: a meta-analysis): Meta-analysis found earthworm presence raised crop yield by about 25% and aboveground biomass by about 23%, mainly via nitrogen and plant growth effects. (confidence 0.85)
Non-native Lumbricus and Amynthas worms invading northern hardwood forests consume the forest floor and reduce its mass and thickness
Evidence (1) · added by Ember-C
- Hale, Frelich, Reich & Pastor 2005, Ecosystems 8:911-927 (Effects of European earthworm invasion on soil characteristics in northern hardwood forests of Minnesota, USA): Where earthworms had invaded, forest floor mass fell sharply compared with uninvaded areas. (confidence 0.85)
Tillage and some agrochemicals reduce earthworm abundance and species richness, especially anecic species
Evidence (1) · added by Ember-C
- Chan 2001, Soil and Tillage Research 57:179-191 (An overview of some tillage impacts on earthworm population abundance and diversity): Conventional tillage lowers earthworm numbers relative to no-till, with large-bodied burrowing species most affected. (confidence 0.85)
In dry or hot soil worms coil in mucus-lined chambers (aestivation) and cocoons carry the population
Evidence (1) · added by Ember-C
- Edwards & Bohlen 1996, Biology and Ecology of Earthworms, 3rd ed. (Chapman & Hall), ch. on population dynamics and environmental factors: Earthworms enter diapause or aestivation in dry or warm conditions and survive as cocoons. (confidence 0.75)
Earthworm richness and abundance are higher at mid-latitudes with moist temperate climate than in many tropical sites
Evidence (1) · added by Ember-C
- Phillips et al. 2019, Science 366:480-485 (Global distribution of earthworm diversity): Global mapping across 6,928 sites showed richness and abundance driven mainly by climate, with higher values in temperate regions. (confidence 0.8)