Haytham Salem, Tong Li, Benfeng Yin, Yuanming Zhang
Biological soil crusts (biocrusts) are photosynthetic soil-surface consortia that stabilize dryland soils, regulate hydrological fluxes, support nutrient cycling, and promote ecosystem recovery. However, inoculation often performs inconsistently because propagules must withstand desiccation, ultraviolet radiation, erosion, transport stress, and repeated wet-dry cycles before functional cover develops. This review evaluates encapsulated carrier-based bioformulation as a microbial delivery strategy for biocrust inoculants. It compares six platform families: dripping ionic gelation, reverse ionic gelation, spray drying, complex coacervation, emulsion or layer-by-layer systems, and capsule, pellet, or seed-ball approaches. Evidence is classified into three levels: direct biocrust delivery studies, close dryland restoration analogues, and transferable microbial encapsulation evidence from biocontrol, probiotic delivery, environmental biotechnology, and agricultural bioformulation. The synthesis supports platform matching rather than a universal carrier. Alginate beads provide the strongest direct support for mixed or fragile biocrust inocula because mild aqueous gelation can accommodate complex propagules and create hydrated microsites. Capsules and pellets offer advantages for handling, microsite placement, delayed release, and co-delivery with seeds or amendments. Spray drying appears more suitable for robust cyanobacterial or algal starter cultures than for intact mixed fragments, whereas reverse ionic gelation, coacervation, emulsion-derived systems, and multilayer coatings remain transferable design concepts. Representative direct studies report controlled-condition establishment within weeks and more than 70% viability after 12 months in selected bead-based systems. Key gaps remain in multi-season field validation, carrier breakdown, residue effects, native-community responses, and platform comparability. Encapsulated biocrust bioformulations should be treated as emerging, evidence-matched restoration tools rather than universal field solutions.