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

Abstract

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.

Keywords: Ecohydrology; Eukaryotes; Forest ecology; Phyllosphere; Stemflow.

Fig. 1

Relative abundance of eukaryotic microbial phyla across ten storm events (refer to Table 1 for event details). Each bar represents the community composition of eukaryotic taxa (color-coded by phylum) for individual stemflow samples after a storm. The two columns in the legend follow the stacking order of the bars: beginning at the bottom right of the legend, then read upward and across to the top of the left column, which corresponds to the top of each stacked bar. Sample identifiers represent individual tree codes in the study plot

Fig. 2

Principal coordinates analysis (PCoA) of stemflow eukaryotic community composition categorized by (top) event and (bottom) NOAA HYSPLIT back-trajectories. Each point represents a sample, color-coded by (top) storm dates and (bottom) the back-trajectory direction of the associated storm: North (N), northwest (NW), southwest (SW), west (W), and south (S)