Sporecasting Biogeography Across Scales: Continental Patterns and Local Constraints on Macrofungal Dispersal.

Understanding how aerial fungal diversity varies across space, habitat, and disturbance is key to linking local-scale sporocarp (fruiting body) reproduction with continental-scale biogeography. In this study, we combined passive spore trap metabarcoding with macrofungal sporocarp records from 31 plots in eight sites across North America to quantify how site, habitat, and fire history shape aerial macrofungal communities. From 823 samples, we recovered 7572 OTUs, nearly half belonging to macrofungi. Macrofungal aerial DNA abundance and OTU richness varied strongly among sites and increased significantly with both temperature and precipitation. Across sites, forest habitats had significantly greater macrofungal aerial DNA abundance than grassland habitats, while conifer forests supported significantly higher OTU richness than oak forests or grasslands. Burn history, likely due to lags in the sampling time following fire, did not significantly impact macrofungal aerial DNA abundance and OTU richness and also had limited effects on community composition. Aerial macrofungal community similarity declined with geographic distance, with geography explaining the most variation (16%). Functional guild composition varied across habitats, shifting from higher ectomycorrhizal prevalence in forest habitats to higher soil saprotroph prevalence in grassland habitats, although wood saprotrophs were the most abundant guild across all habitats. Integration with iNaturalist sporocarp records indicated a mean effective spore trap input range of ~3 km, consistent with strong local dispersal limitation. Together, these findings demonstrate that aerial macrofungal assemblages exhibit pronounced continental-scale structure yet remain locally heterogeneous, shaped primarily by environmental filtering, functional guild association, and limited dispersal.