Fungal Endophyte-Infected Leaf Litter Alters In-Stream Microbial Communities and Negatively Influences Aquatic Fungal Sporulation

Endophytes are ubiquitous plant‐associated microbes and although they have the potential to alter the decomposition of infected leaf litter, this has not been well‐studied. The endophyte Rhytisma punctatum infects the leaves of Acer macrophyllum (bigleaf maple), causing the appearance of black ‘tar spots’ that persist in senesced leaves. Other foliar fungi also cause visible damage in healthy tissues of this host plant system including an unidentified bullseye‐shaped lesion, common in western Washington. Using three treatments of endophyte infection status in leaf tissue (R. punctatum‐infected, bullseye‐infected, lesion‐free), leaf litter discs were submerged in a third‐order temperate stream using mesh litter bags and harvested periodically over two months to determine the effects of litter treatment and incubation time on litter mass loss, fungal sporulation, and microbial community colonization. Litter containing symptomatic endophyte infections (Rhytisma or bullseye) had reduced sporulation of aquatic hyphomycetes, but decomposed significantly faster than lesion‐free or bullseye‐infected litter. Using amplicon‐based sequencing, we found a significant difference in bacterial communities colonizing Rhytisma‐infected and bullseye‐infected leaf litter, a significant difference in fungal communities colonizing Rhytisma‐infected leaf litter compared to the two other treatments, and a change in both community structure and relative abundances of bacterial and fungal taxa throughout the study period. Indicator Species Analysis clarified the drivers of these community shifts at the genus level. Our results show that endophyte‐associated, in‐stream sporulation and microbial community effects are observable within one species of leaf litter