Stage-specific cyanobacterial handoffs and heterotrophic subsidies underpin biocrust carbon accumulation.

Inoculating cyanobacteria is a widely adopted strategy to accelerate biocrust formation and restore dryland soil functions, yet the in situ mechanisms sustaining microbial biomass carbon (MBC) accumulation under seasonal stress remain poorly understood. Here, we combined a field inoculation experiment with multi-omic profiling (amplicon sequencing, metagenomics, metatranscriptomics, and metaproteomics) and genome-scale metabolic modeling to track the circannual development of induced cyanobacterial biocrusts in Hopq Desert, China. Although the inoculated Konicacronema strain (formerly Microcoleus) maintained significant taxonomic dominance, metatranscriptomic and metaproteomic data revealed a striking functional handoff. Microcoleus-like populations drove rapid initial biocrust formation via the oxidative pentose-phosphate pathway and enzymatic antioxidant systems, whereas Oscillatoria assumed transcriptional dominance during harsher seasonal transitions through enhanced light harvesting, cyclic electron transport, and non-enzymatic photoprotection. Genome-scale metabolic modeling predicted that dominant cyanobacteria acted primarily as net importers, receiving amino acids, vitamins, cell-wall precursors, and phosphate from heterotrophic partners, while supplying inorganic sulfur and iron-sulfur clusters. Co-occurrence networks and life-history analyses further revealed that MBC maintenance was associated with a shift from growth-oriented resource mobilization toward acquisition-oriented strategies mediated by ABC transporters. Structural equation modeling confirmed that solar radiation and soil salinity govern MBC indirectly by influencing cyanobacterial composition and the balance between phototrophic assimilation and resource-acquisition strategies. These findings demonstrate that biocrust carbon accumulation is sustained by temporal functional division among cyanobacterial guilds and metabolic subsidies from heterotrophic partners, rather than by the persistent activity of a single pioneer strain, and provide a trait-based roadmap for designing resilient, multifunctional synthetic inocula for dryland restoration.