A Comprehensive Review of the Role of Biological Soil Crusts in Enhancing Soil Fertility, Moisture Conservation, Erosion Control, and Ecosystem Resilience

This review article analyzes research studies conducted between 1980 and 2025, examining the role of biological soil crusts (BSCs) in improving soil fertility, regulating hydrological processes, and reducing soil erosion in arid and semi-arid ecosystems, with special emphasis on the effectiveness of artificial inoculation approaches. Quantitative evidence indicates that BSCs significantly reduce erosion depending on crust type, successional stage, coverage percentage, and spatial scale. Cyanobacterial crusts have achieved approximately 77-99% reduction in erosion in many field and laboratory experiments, while moss crusts with adequate coverage have resulted in nearly 100% reduction in surface erosion and, in some cases, dust emission. At various scales, this function depends on microtopography, within-community heterogeneity, and establishment patterns. During early successional stages, cyanobacteria and bacteria provide the initial core of the surface restoration process through the production of extracellular polysaccharides, nitrogen fixation, soil aggregate formation, and increased soil structural cohesion. A comprehensive review of experimental studies demonstrates that single-application of artificial inoculation of these microorganisms during late summer on loose, erosion-prone soils, while substantially reducing runoff and sediment, enables faster formation of stable crusts and reduces recovery time from natural multi-decadal periods to approximately 5-10 years. The implementation cost of this approach is typically reported to be around $350 per hectare. In advanced successional stages, mosses, upon achieving coverage greater than approximately 36%, become the most effective factor in reducing erosion and improving surface stability. Simultaneously, by altering the moisture and thermal regimes of the surface layer, they affect evaporation, infiltration, and water redistribution at both patch and bulk scales. These results indicate that targeted use of artificial BSC inoculation, combined with moss cover management, represents an efficient and accelerating approach for erosion control, enhanced fertility, and optimization of soil hydrological behavior in land restoration programs. Given the moisture-thermal regimes of Iran, the inoculation of native cyanobacteria, such as Phormidium spp. and Scytonema spp. , at an optimal concentration of 100 million cells per liter (10⁸ cells L⁻¹) during late autumn is proposed as a practical operational strategy. This approach establishes an appropriate balance among cost, microbial survival, restoration efficiency in arid climates, and ecosystem equilibrium.