- Also called:
- cryptobiotic soil crust, microbiotic soil crust, or cryptogamic soil crust
- Related Topics:
- Bacteria
- soil
- Algae
- Blue-green algae
- microfungus
Biological soil crust
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What is a biological soil crust?
A biological soil crust is a thin layer of living material that inhabits the uppermost millimeters of soil. It is composed of specialized organisms that bind soil particles together. These crusts are typically found in open, dry, and extremely cold regions across continents, where harsh conditions limit the growth of vascular plants.
Key functions of biological soil crusts:
* Soil stabilization
* Water retention
* Soil fertility
* Carbon fixing
* Nitrogen fixingThe organisms within these crusts have adaptive strategies, such as low moisture requirements and tolerance to extreme temperatures, that enable them to thrive in harsh environments. However, these crusts are fragile and susceptible to mechanical disturbances, with recovery taking decades to centuries.
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Which organisms make up a biological soil crust?
Biological soil crusts are thin layers of living material in the uppermost soil, crucial for soil stabilization, water retention, and fertility. They're found in dry and cold regions, where they can constitute over 70% of ground cover.
These crusts are composed of various organisms, including cyanobacteria and other bacteria, microfungi, algae, lichens, and mosses. Cyanobacteria and green algae are typically the first to colonize bare ground, followed by lichens and mosses once the soil is more stable. Microcoleus, a filamentous cyanobacteria, is a common genus that provides the crusts' cohesive quality by secreting a sticky mucilage that binds soil particles.
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Where are biological soil crusts usually found?
Biological soil crusts are typically found in open spaces within dry and extremely cold regions across all continents, where harsh conditions limit the growth of vascular plants. These crusts are especially well-developed in many areas, often constituting over 70 percent of the living ground cover. They play a crucial role in soil stabilization, water retention, and overall soil fertility, significantly influencing global ecosystems.
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How do biological soil crusts help prevent soil erosion?
Biological soil crusts prevent soil erosion through the combined actions of their living organisms. Filamentous cyanobacteria, a common component of soil, generate much of the crusts' cohesive nature. These microbes move through the soil when moistened and leave behind a sticky trail of mucilage that binds soil particles together. Additionally, the rough surfaces of these crusts slow rainwater runoff, which boosts water infiltration into the soil. These crusts can absorb up to 10 times their volume in water and slowly release it into the soil.
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How do biological soil crusts contribute to a desert ecosystem?
Biological soil crusts are essential to desert ecosystems, as they help with soil stabilization, water retention, and fertility in harsh environments that inhibit plant production. Composed of cyanobacteria, microfungi, algae, lichens, and mosses, these crusts can cover over 70% of the ground in dry regions.
Notably, the crusts convert atmospheric nitrogen into organic compounds, which enriches the soil, and their rough surfaces slow rainwater runoff, improving water infiltration. They also absorb and slowly release water, holding up to 10 times their volume, which is vital in deserts where water is scarce. However, these crusts are fragile and slow to recover from disturbances.
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What threats do biological soil crusts face, and how can we protect them?
Biological soil crusts, vital for soil stabilization and fertility, face significant threats, primarily from mechanical disturbances like vehicles and trampling by people or animals. When dry, the cyanobacterial filaments, mosses, and lichens that make up these crusts are brittle and easily crushed.
Protection measures include reducing greenhouse gas emissions through economic policies and technical measures, as climate change and desertification are closely related. On a local scale, solutions involve sustainable land and soil management, such as cover crops, crop rotation, and rotational grazing. These practices help maintain soil productivity and prevent erosion. It's important to note that recovery of damaged crusts can take decades to centuries, highlighting the need for proactive conservation.
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Biological soil crust, thin layer of living material formed in the uppermost millimetres of soil where soil particles are aggregated by a community of highly specialized organisms. Biological soil crusts are found primarily in open spaces in the dry and extremely cold regions of all continents, where harsh conditions inhibit vascular plant production. In many areas the crusts are extraordinarily well developed and can represent more than 70 percent of the living ground cover. Biological soil crusts are key for soil stabilization, water retention, and soil fertility and are recognized as having a major influence on global ecosystems.
Biological components of the crusts include cyanobacteria and other bacteria, microfungi, algae, lichens, and mosses. Cyanobacteria and green algae are generally the first to colonize bare ground, followed by lichens and mosses, which require stable soil strata for growth. The filamentous cyanobacteria of genus Microcoleus, which are commonly found in soil, provide much of the cohesive quality of the crusts. Those microbes secrete sticky mucilage around their cells and filaments. When moistened, they move through the soil and leave a trail of sticky mucilaginous sheath material behind that glues soil particles in place.
Biological soil crusts can be classified into four categories based on crust morphology: (1) flat, which occur in areas where freezing is rare and cyanobacteria dominate, (2) rugose, which occur in areas where freezing is rare and lichens or mosses dominate, (3) pinnacled, which are found in areas where freezing and frost heaving are common and cyanobacteria dominate, and (4) rolling, which prefer areas where freezing and frost heaving are common but lichens or mosses dominate.
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Biological crust organisms possess adaptive strategies that allow them to survive in extreme habitats on Earth. For example, they have low moisture requirements and can survive on small amounts of rainfall, fog, and dew as water sources. They are poikilohydric (capable of drying out and suspending respiration for an extended period of time); when wet, their metabolic functions begin almost immediately. They also can tolerate extreme temperatures in a desiccated state.
Biological crusts carry out myriad ecological roles. They are important sources of fixed carbon in sparsely vegetated areas. Cyanobacteria and cyanolichens in the crusts convert atmospheric nitrogen into organic compounds that leak into surrounding soil, which is especially important in desert ecosystems where low soil nitrogen levels often limit plant growth. Crusts with roughened surfaces slow rainwater runoff and increase water infiltration into the soil. After sporadic rainfall, crust organisms and their mucilage absorb up to 10 times their volume in water and later release the water slowly into the soil.
When dry, cyanobacterial filaments, mosses, and lichens are brittle and crush easily. As a result, mechanical disturbances, such as from vehicles and trampling by people or animals, pose significant threats to biological crusts. After disturbance, biological crust recovery may take 250 to 1,000 years in very dry regions; even in places that are relatively moist, recovery can take 20 years.