Biological Soil Crusts in Dryland Ecosystems

Biological soil crusts, or biocrusts, are surface assemblages of microorganisms and cryptogams—including cyanobacteria, microalgae, lichens and mosses—that form a cohesive layer on arid and semi-arid soils. They occupy the interface between the soil and the atmosphere, where they stabilise sediments through filamentous networks and extracellular polymers, enhance water infiltration by modifying surface roughness, and contribute to carbon and nitrogen inputs via photosynthesis and biological fixation. Biocrust communities undergo successional development, from pioneer cyanobacterial mats to complex bryophyte- and lichen-dominated assemblages. Their global extent spans deserts, dry steppes and polar semi-deserts, making them critical modulators of soil fertility, erosion control and hydrological routing. Moreover, by altering surface albedo and soil thermal regimes, biocrusts influence local microclimates and may feed back to broader climatic processes. They also interact dynamically with vascular plants, sometimes facilitating seedling establishment and at other times inhibiting germination, depending on crust composition and plant traits. Recognition of these multifaceted roles has spurred efforts to harness biocrusts for ecosystem restoration, desertification mitigation and sustainable land management in drylands worldwide.

Research from Nature Portfolio

Recent analyses have revealed that mature biocrusts rich in late-successional cyanobacteria accumulate scytonemin, a UV-protective pigment, leading to a measurable increase in soil surface temperature of up to 10 °C. This microbial ‘sunscreen’ effect reduces albedo and reshapes microbial community composition toward thermotolerant taxa. Complementary experimental work under simulated warming and altered precipitation regimes on North American drylands has shown that disturbance-induced loss of mosses and lichens raises surface reflectance by over 30 %, indicating rapid shifts in energy balance following foundation species mortality. These findings underscore the capacity of biocrusts to mediate land-atmosphere feedbacks and suggest that climate change may trigger threshold responses with consequences for soil temperature, moisture dynamics and ecosystem resilience.

Biological Soil Crusts in Dryland Ecosystems publication trend

The graph below shows the total number of articles in biological soil crusts in dryland ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Biological soil crust (biocrust): A cohesive layer of cyanobacteria, algae, lichens and mosses on the soil surface of drylands that stabilises soil and mediates biogeochemical cycles.

Cyanobacteria: Photosynthetic bacteria that are often the initial colonisers of bare soil, producing filaments and exopolymers that bind particles and fix atmospheric nitrogen.

Exopolysaccharide (EPS): High-molecular-weight polymers secreted by microbes that enhance soil particle adhesion and water retention.

Albedo: The proportion of incoming solar radiation reflected by a surface; low albedo surfaces absorb more heat.

Diazotroph: An organism capable of converting atmospheric nitrogen into bioavailable forms through biological nitrogen fixation.

References

1. The Microbiology of Biological Soil Crusts. Annual Review of Microbiology (2023).
2. Cyanobacteria Inoculation Improves Soil Stability and Fertility on Different Textured Soils: Gaining Insights for Applicability in Soil Restoration. Frontiers in Environmental Science (2018).
3. Bacteria increase arid-land soil surface temperature through the production of sunscreens. Nature Communications (2016).
4. Albedo feedbacks to future climate via climate change impacts on dryland biocrusts. Scientific Reports (2017).
5. Towards a predictive framework for biocrust mediation of plant performance: A meta‐analysis. Journal of Ecology (2019).
6. Biological soil crust and disturbance controls on surface hydrology in a semi‐arid ecosystem. Ecosphere (2017).