Soil Crust

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Introduction

Biological soil crusts (BSC) are large complex communities of cyanobacteria, algae, bryophytes, [Lichens], mosses, [bacteria], and fungi. These diverse collections of microbes occur all over the world in arid and semi-arid regions, which comprise more than 35% of all terrestrial land. The microbial community that inhabits the upper and bottom few millimeters of soil can comprise up to 70% of the living cover in arid regions. BSC can play an important role in desert environments as they increase the nutrient content of soils, stabilizing soil surfaces, as well as prevent soil erosion.

Environment

BSC are a key component of stabilizing mobile surfaces by binding soil particles together with polysaccharide exudates, and a matrix of fibers. The binding of the surface particles help protect from wind and water erosion as well as cryoturbation.


Physical

Formation of these soil crusts begin with interactions between colonizing fungi and cyanobacteria. Microcoleus is a type of cyanobacteria that will form filaments surrounded by extracellular sheats. The filaments are mobile through the moist soil. Filaments are of this cyanobacteria are in constant regeneration creating stable soil aggregates. Other common cyanobacteria found in BSC are [Nostoc ], Scytonema, Calothrix, and Gloeocapsa. Once cyanobacteria and fungi have created a stable platform, other organisms such as lichens, algae, and mosses will begin a secondary succession.


Biological interactions

The changes these microbes make to the soil structure create a more suitable habitat and enhance the ability of vascular plant species to reproduce in arid environments. Organisms in the BSC increase moisture, organic matter, and nutrient content. This is important in arid regions as all those variables are the limiting factor in plant growth.

BSC are highly sensitive to water content. Larger concentrations of water increase the diffusion of CO2 and O2 disturbance by surface water. Decrease in amounts of water cause algae to be less productive causing an overall drop of photosynthesis in BSC. An increase in temperature has also shown decreases in photosynthesis production.


Microbial processes

Cyanobacteria

BSC that have a large amount of cyanobacteria present are generally expected to have higher nitrogen content due to the N-fixation of cyanobacteria .

Lichens and Arthropods

Lichens are an important component to the food web of soil crusts. Many types of arthropods use lichens as a food source. Microarthropods are essential to nutrient cycling as the contribution they have in BSC increases the microbial turnover. Microarthropods enhances leaching of soluble materials that promotes microbial colonization by increasing surface area. Some of the more commonly found microarthropods in warm deserts are Acari and Prostigmata. Disturbances to lichen communities are difficult to recover. Lichens are slow to grow with recovery spaning from 5 to over 500 years making lichens a fragile species to BSC.

Organism

Protozoa

Nematodes

Cyanobacteria

[Lichens]

Algae

Ahtropods

Bryophytes

Mosses

Fungi

Current Research

Enter summaries of recent research here--at least three required

References