Ecology of Biological Soil Crusts and Associated Microorganisms

Abstract

Biological soil crusts (BSCs) develop when surface soil particles are consolidated by microorganisms into stable surface crusts. BSC microorganisms include viruses, non-symbiotic and lichenized fungi, archaea, bacteria, cyanobacteria, terrestrial microalgae, and tiny mosses. Most early research concluded that BSCs were limited to arid areas or deserts, not because of their absence elsewhere, but because they were most visibly conspicuous there. BSC habitats were historically referred to as glades , barrens , and balds in the USA, and as inselbergs , alvars , and the Burren in Europe. Although still most evident in deserts, BSCs have been observed in most ecosystems worldwide. In mesic climes, BSCs occur where physical perturbation, fire, or some other form of disturbance has removed or significantly reduced the vascular plant overstory. Microorganisms that create BSCs are tiny, lightweight, and easily attached to windborne dust particles. They regularly fall to Earth from the upper atmosphere and outer space. In addition to the soil, BSC microorganisms are present on most exposed surfaces, including plants, animals, rocks, buildings, vehicles, gravestones, ice, snow, water, etc. BSC microorganisms have been recorded in aerial, edaphic, and aquatic environments worldwide. When inhaled by humans or other animals, they become components of the respiratory microbiome. BSCs are thought to be negatively affected by global warming, although many studies have revealed their persistence for millions of years through multiple cycles of global warming and cooling. BSC microorganisms protect Earth from the potential negative effects of global warming by sequestering atmospheric carbon dioxide into organic matter.