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Biosphere as a Living Place


Biological Soil Crusts
The Hidden Biome

 

A very common biome exists all over the world that is very good at being unnoticeable. This biome is part of dry places all over the world. We call such places arid or semi-arid; they don't get much rain. The common name is desert. The biome is called Biological Soil Crust, which means the crust is alive and vulnerable, like every living thing. But it often does not look alive. It may often look dry, dead and immobile, but it is not. The only times it may look alive is after it rains, which seldom happens in deserts. This bilogical community is dormant most of the time. When it gets wet, the bilogical soil crust metabolizes and kicks into high gear.

Biological soil crusts are communities of life, a crust of soil particles bound together by organic materials.They are miniature ecosystems that are the interface between air and soil, a kind of ecotone. Living crusts provide much of the usable nitrogen that deserts generate, crucial to all vegetation. Check out Crust 101: http://www.soilcrust.org/crust101.htm


     
  Under 6" soil depth stabilized by crust in rock Image© USGS Canyonlands     Desert pavement in the Mojave Desert, CA
Image courtesy Wikipedia
     
  biological soil crust crushed by tires
Image© USGS Canyonlands
    one kind of physical soil crust
image credit Portland State University


Some soil crusts are inorganic, purely physical. Many physical crusts develop over a long time by raindrops hitting soils. Some are formed by crushing or trampling by tires and animal hooves. Salt flats form chemically, often as pooled water evaporates. Desert pavement (above) is a crust formed of small stones under flowing water. Most Physical crusts are hard and smooth. Pressure seals soil surfaces. Windblown organic matter does not stay. Water runs off instead of sinking in, encouraging erosion and flooding. Seeds don't germinate.

Living soil crusts are rough rather than smooth. Organic matter that blows in is welcome to stay, decay and make more soil. Rain percolates down rather than running off. Although living crusts often cover the spaces between spaced desert plants, seeds are welcome to take their chances.

How is a soil crust structured? What does it look like inside?

3D soil crust schematic --- Click to enlarge Key to common names for diagram left,
clockwise from top

Bryum


Moss

Peltigera

Lichen

Fulgensia

Lichen

Nostoc


Cyanobacteria

Calothrix

 

Cyanobacteria

Endocarpon


Lichen

Catapyrenium



Lichen

Nostoc

 

Cyanobacteria

Macrochloris

 

Green algae

Microcoleus

Cyanobacteria

Who are the fundamental community members in a living soil crust?

 

Member Name  

Process

 

Provides to crust community

  Cyanobacteria   photosynthesis; releases minerals
fixes nitrogen, binds soil
  Nitrogen, carbon (food),oxygen, and glues soil together with its sticky filaments. Releases acids that degrade minerals and make them available
  Green Algae   photosynthesis   carbon compounds (food), oxygen
  Fungi   decays dead tissues so nutrients cycle, bind soil   defense and re-cycling nutrients: carbon, nitrogen, more
  Lichen   photosynthesis, sometimes nitrogen fixing   carbon compounds (food), oxygen, nitrogen if the partner is cyanobacteria
  Moss and Liverworts   photosynthesis, binds soil   carbon compounds, oxygen, provide nitrogen at death
  Soil protists   graze excess bacteria and other protists   balance in the trophic web (feeding network),
provide nitrogen at death

Most biological soil crusts begin with a cyanobacterium spreading its sticky filaments through the local soil. Soil fungi quickly join, as will local chlorophyte algae and diatoms in the neighborhood. Bacteria are everywhere and quickly sort out what kinds best flourish here. Like all communities, biological soil crusts develop through ecologicl succession. The dominant members of early communities usually are cyanobacteria. As they mature, living crusts tend to be dominated by lichens and with them, mosses and liverworts. Varying microclimates and climate changes alter alternative patterns of maturity.

Biological soil crust types in North American deserts. Click to enlarge.

fishook cactus seedling in pinnacle soil crust in Utah
image credit USGS Canyonlands

seedling cactus next to rugose-type soil crust in Baja Mexico Sonoran desert
image credit John Caddy

Mature scale lichen bio-soil crust in Baja Mexico Sonoran desert
image credit John Caddy

Pinnacle-type soil crust in cool desert
image credit University of Arizona
Rugose bio-soil crust covers space between plants
image credit Neal Herbert, NASA
Mature scale-lichen biological soil crust in Utah desert
image credit USGS Canyonlands
Grand Canyon pinnacle soil crust
image credit USGS Canyonlands
Blushing scale mini-lichen mature soil crust, Utah
image credit USGS Canyonlands
Mature bio-soil crust dominated by moss
image credit USGS Canyonlands
Rugose-type bio-soil crust begins to bury land snail shells in Baja, Mexico desert
image credit John Caddy
seedling takes root in pinnacled bio-soil crust
image credit Neal Herbert NASA
Colorfull mini-lichens shape a mature
bio-soil crust in Utah desert
image credit USGS Canyonlands

Many Australian mature biological soil crusts are lichen and moss dominated. Notice the dramatic difference below between the dry crust and the crust wetted, two minutes later.
Water jump-starts metabolism Click to enlarge

biological soil crust in normal dry state
© 2012 Australian National Botanic Gardens and Australian National Herbarium, Canberra

biological soil crust wthin two minutes of wetting
© 2012 Australian National Botanic Gardens and Australian National Herbarium, Canberra
This diagram helps explain what is shown in the two photos above. Yellow dots show lichens, blue dots show mosses and the one liverwort is marked by red .
© 2012 Australian National Botanic Gardens and Australian National Herbarium, Canberra

 

Explore Further in the Biosphere

 
Biosphere: Introduction
 
Biosphere as Place: Introduction
 
Biosphere as Ocean: Life Zones
 
Biosphere as Ocean Floor: Benthic Biomes One
 
Biosphere as Ocean Floor: Benthic Biomes Two
 
Biosphere on Land: Terrestrial Biomes
    Biosphere on Land: Biological Soil Crusts
 
Biosphere on Land: Anthropogenic Biomes
 
Biosphere as Process: Introduction
 
Biosphere Process: Floating Continents, Tectonic Plates
 
Biosphere Process: Photosynthesis
 
Biosphere Process: Life Helps Make Earth's Crust
 
Biosphere Process:
Rock Cycle--Marriage of Water and Rock
 
Biosphere Process: Marriage of Wind and Water
   
Biosphere Process: Gas Exchange
 
Biosphere as An Expression of Spirit
 
The Ecological Function of Art
 
The Earth Goddess
 
The Tree of Life
 
The Green Man
 
Earth Art
 
Biosphere as Community
 
Biosphere Microcosm: Bacteria and Archaea
The Procaryote Domain
 
Biosphere Microcosm: Germs
 
Biosphere Community: The Eucaryote Domain
 
Biosphere Community: Protists 1: Algae
 
  Biosphere Community: Protists 2: Protozoa
 
Biosphere Community: Plants: What's New?
 
Biosphere Community: Plant Diversity--Major Groups
 
Biosphere Community: Plant Defense
 
Biosphere Community: Plant Pollination
   
Biosphere Community: Plant Seed Dispersal
 
Biosphere Community: Kingdom Animals
 
Biosphere Community: Kingdom Fungi
 
Biosphere Community: Six Great Extinctions
 
Return to Ecology Index

 

copyright © Morning Earth 2013

 

 

 




 

 

 

 

 

 

 

 

 

 

 

Explore Further in Biosphere

 
Biosphere: Introduction
 
Biosphere as Place: Introduction
 
Biosphere as Ocean: Life Zones
 
Biosphere as Ocean Floor: Benthic Biomes One
 
Biosphere as Ocean Floor: Benthic Biomes Two
 
Biosphere on Land: Terrestrial Biomes
 
Biosphere on Land: Anthropogenic Biomes
 
Biosphere as Process: Introduction
 
Biosphere Process: Floating Continents, Tectonic Plates
 
Biosphere Process: Photosynthesis
 
Biosphere Process: Life Helps Make Earth's Crust
 
Biosphere Process:
Rock Cycle--Marriage of Water and Rock
 
Biosphere Process: Marriage of Wind and Water
   
Biosphere Process: Gas Exchange
 
Biosphere as An Expression of Spirit
 
The Ecological Function of Art
 
The Earth Goddess
 
The Tree of Life
 
The Green Man
 
Earth Art
 
Biosphere as Community
 
Biosphere Microcosm: Bacteria and Archaea
The Procaryote Domain
 
Biosphere Microcosm: Germs
 
Biosphere Community: The Eucaryote Domain
 
Biosphere Community: Protists 1: Algae
 
  Biosphere Community: Protists 2: Protozoa
 
Biosphere Community: Plants: What's New?
 
Biosphere Community: Plant Diversity--Major Groups
 
Biosphere Community: Plant Defense
 
Biosphere Community: Plant Pollination
   
Biosphere Community: Plant Seed Dispersal
 
Biosphere Community: Kingdom Animals
 
Biosphere Community: Kingdom Fungi
 
Biosphere Community: Six Great Extinctions
 
Return to Ecology Index

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