by Mechas
Have you ever heard of biocrusts? If not, you are not alone. I only stumbled upon this term recently and was surprised to find that it represents a growing field of research on what appear to be fragile, surface soil communities that are just the opposite. Biocrusts are incredibly resilient to inhospitable conditions.
To be clear, the definition of biocrusts, short for "biological soil crusts," is still under construction and undergoing revisions mainly because this is an evolving field of study. Biocrusts are communities of organisms that live on the surface of the soil, often forming austere and uninviting layers covering desolate and arid environments. They occur worldwide, covering about 12% of the Earth's surface, but are mostly evident in locations with limited vascular plant cover, such as deserts or polar regions. Biocrusts also have different forms and functions, depending on their location and the environmental conditions. But more importantly, they are not just any soil community. In fact, a recent effort to consolidate a definition of a biocrust pointed out several cases in which the term would not be appropriate, such as marine microbial mats.
Fig. 1. Biocrust definition illustrated in a Venn diagram. Ovals represent the four major elements of the proposed biocrust definition. Biocrusts are consistent with the region where all four overlap. Other ‘outgroups’ are also mapped and labelled on the diagram, with the main reasons for their distinction from biocrusts listed. Parenthetical numbers indicate the relevant section in the review. Source Frontispiece: Biological soil crust in Natural Bridge National Monument. Source
The identification of a biocrust depends on a few essential characteristics: their habitat and the formation of thin, hardened, layered structures, their functional properties and taxonomic composition (Fig. 1). The resulting definition, though long, broadly designates biocrusts as being mixed communities of photoautotrophic (like cyanobacteria, algae, lichens or bryophytes) and heterotrophic (other bacteria, fungi and archaea) organisms that live and form a coherent layer on the uppermost millimeters of soil.
But why do I find biocrusts interesting? Other than the fact that I had never heard of this term before, these biocrusts are important for soil vitality and productivity. Because they grow in places with little vegetation, they help stabilize the soil surface and limit erosion by wind and water. These communities also provide nutrients and influence water availability. Given the vast extensions of soils covered by these biocrusts, any disturbances resulting from changing climate conditions and land use will certainly have a deep effect on soils on a global scale. Just one more thing to worry about.
Definitions notwithstanding, these hardy and ecologically important communities awaken (again) a sense of awe at the capacity of life to adapt to less than amiable conditions on this planet. Structurally fragile yet biologically resilient, biocrusts are set to teach us more about how to withstand adversity.
Do you want to comment on this post? We would be happy about it! Please comment on Mastodon or Bluesky.
Comments