Construction of composite biological soil crusts accelerates early-stage soil restoration in karst rocky desertification areas

Karst rocky desertification (KRD) represents one of the most severe forms of land degradation globally. Soils in these regions are characterized by structural instability, severe nutrient depletion, and fragmented microbial networks, all of which collectively impose formidable constraints on natural biogeochemical recovery. In this study, we experimentally induced biological soil crusts (BSCs) through the use of moss, algae, and their co-inoculation, which represents a composite BSCs construction strategy, under both controlled and field conditions. We specifically examined how inoculation strategy regulates carbon–nitrogen coupling, nutrient pools, enzyme activities, dissolved organic matter transformation, and microbial community reorganization over 90 days. Results showed that co-inoculation acted as the dominant driver of early-stage ecosystem restoration. It increased Chl a up to tenfold, enhanced total organic carbon, and elevated nitrate concentrations by up to fivefold under controlled conditions, accompanied by a 40–43% rise in urease activity. Coordinated increases in sucrase, urease, and alkaline phosphatase indicated enhanced microbial C-N-P acquisition. Concurrently, DOM shifted toward greater microbial contribution with early-stage humification signals. Microbial richness more than doubled, communities transitioned from unicellular to filamentous nitrogen-fixing cyanobacteria, and saprotrophic Ascomycota became dominant, alongside enrichment of nitrogen-reduction and complex carbon-degradation pathways. Collectively, these findings demonstrate that induced BSCs promote early-stage nutrient accumulation and microbial community reorganization in soils within KRD areas. Moss-cyanobacterial co-inoculation consistently outperformed single inoculation treatments under both indoor and field conditions. The study underscores the potential of induced BSCs technology as a promising ecological strategy for the early restoration of degraded soils within KRD area.