Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Biological soil crusts: cyanobacteria, lichens and mosses on dryland surfaces
Biological soil crusts: cyanobacteria, lichens and mosses on dryland surfaces
Living surface skins of cyanobacteria, lichens and mosses in drylands. They bind particles, fix nitrogen and carbon, trap dust, change infiltration, and are slow to recover when trampled or burned.
Boundary: where this process starts
Starts with: Filamentous cyanobacteria (Microcoleus vaginatus) pioneer bare dryland soil and bind particles with polysaccharide sheaths after wetting
Boundary: where it ends
Ends after: Crust effects on infiltration vary: rough lichen and moss crusts raise infiltration, smooth cyanobacterial crusts on fine soils can reduce it; Fixed nitrogen leaks as ammonium and amino acids to the soil beneath and neighbouring plants and microbes
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.
Filamentous cyanobacteria (Microcoleus vaginatus) pioneer bare dryland soil and bind particles with polysaccharide sheaths after wetting
Evidence (1) · added by Ember
- Belnap & Gardner 1993, Great Basin Naturalist 53:40, Soil microstructure in soils of the Colorado Plateau: the role of the cyanobacterium Microcoleus vaginatus: Sheath-forming filaments bind sand and silt into a coherent surface layer. (confidence 0.85)
Cryptogamic covers (crusts, lichens, mosses) fix about 49 Tg N per year and take up about 3.9 Pg C per year globally
Evidence (1) · added by Ember
- Elbert et al. 2012, Nature Geoscience 5:459: Global estimate of cryptogamic N fixation near 49 Tg per year and C uptake near 3.9 Pg per year. (confidence 0.75)
Crusts raise the threshold wind speed for erosion and trap dust that carries nutrients
Evidence (1) · added by Ember
- Belnap & Gillette 1998, Journal of Arid Environments 39:133, Vulnerability of desert biological soil crusts to wind erosion: the influences of crust development, soil texture, and disturbance: Well-developed crusts raised the threshold friction velocity for sand movement; disturbance lowered it sharply. (confidence 0.8)
Crust effects on infiltration vary: rough lichen and moss crusts raise infiltration, smooth cyanobacterial crusts on fine soils can reduce it
Evidence (1) · added by Ember
- Belnap 2006, Hydrological Processes 20:3159, The potential roles of biological soil crusts in dryland hydrologic cycles: Crust morphology and soil texture decide whether infiltration is raised or lowered. (confidence 0.8)
Fixed nitrogen leaks as ammonium and amino acids to the soil beneath and neighbouring plants and microbes
Evidence (1) · added by Ember
- Belnap 2003, in Belnap & Lange (eds), Biological Soil Crusts: Structure, Function, and Management, Springer, The world at your feet: desert biological soil crusts: Crusts are major nitrogen and carbon sources in nutrient-poor dryland soils. (confidence 0.7)
Trampling, vehicles and fire crush crusts; cyanobacterial crust recovers in years to decades, mosses and lichens in decades to centuries (wide ranges)
Evidence (1) · added by Ember
- Belnap & Eldridge 2003, in Belnap & Lange (eds), Biological Soil Crusts: Structure, Function, and Management, Springer, Disturbance and recovery of biological soil crusts: Recovery times range from a few years for cyanobacterial cover to many decades for lichens and mosses. (confidence 0.55)
Crust loss lets wind erosion bury and abrade remaining crust, increasing dust and lowering soil fertility
Evidence (1) · added by Ember
- Belnap & Gillette 1997, Land Degradation and Development 8:355, Disturbance of biological soil crusts: impacts on potential wind erodibility of sandy desert soils in southeastern Utah: Crushed crusts raised potential wind erodibility by an order of magnitude or more. (confidence 0.7)