Community Composition of Microbial Eukaryotes Transported by Stemflow from Fagus grandifolia Ehrh. (American Beech) Trees in Northeastern Ohio (USA)

Stemflow, the concentrated fraction of rainfall that drains down tree trunks, can translocate canopy biota to the forest floor, but its eukaryotic composition remains uncharacterized via eDNA methods. We collected stemflow from 18 Fagus grandifolia (American beech) trees during ten storms in northeastern Ohio (USA) and analyzed 18S rRNA eDNA to resolve transported microbial-eukaryote communities. Over 12 million reads (83 samples) revealed 920 zero-radius OTUs spanning fungi, algae, protists, and metazoans. Community composition differed significantly among storm events (PERMANOVA F = 3.6, r² = 0.31, p < 0.001) and among NOAA HYSPLIT modeled air-mass back-trajectories (F = 8.9, r² = 0.36, p < 0.001). Summer storms were dominated by fungal taxa (Entomophthoromycota, Basidiomycota, and Ascomycota comprised up to 90% of reads), whereas late-autumn and winter storms carried mainly algal stramenopiles (Ochrophyta). Large storms (> 60 mm event^-1) mobilized conspicuously higher relative abundances of larger metazoans (tardigrades and arthropods). We infer from stemflow eDNA that (i) seasonal resource shifts in tree canopies favor parasitic fungi in summer and saprotrophic fungi in autumn; (ii) northerly winter storms entrain Great Lakes aerosol algae that deposit onto canopies; (iii) rainfall intensity and duration jointly control the detachment of well-attached canopy eukaryotes. Together, our results establish stemflow eDNA as a non-invasive window into storm-mediated linkages between above- and below-ground biodiversity, offering new scope for monitoring canopy microbiomes under intensifying hydro-climatic regimes.