The ability of foliar fungal endophytes to modify leaf litter decomposition following host senescence has been empirically demonstrated, but how this manipulation affects nutrient cycling and host plant competitive outcomes is poorly understood. Additionally, the ability of endophytic taxa to alter realized microbial community composition in leaf litter through priority effects is little explored. Previously, we demonstrated the existence of a highly-specialized symbiosis between a new family of fungi, Catenasporaceae, and a temperate fern host in the Pacific Northwest. These fungi colonize fern tissue as endophytes through aerial sporulation events. When host leaves senesce, the fungi undergo sexual reproduction and recolonize tissue of the same host in a process we call gyrofolius transmission. Since we observed a strong association between the abundance of these fungi and the presence of recalcitrant fern litter in natural habitats, we examined whether Catenasporaceae is indeed responsible for slowing litter decomposition around fern hosts and how this litter affects the recruitment of interspecific competitor plants. In a separate but related study, we explored how the incidence of two symptomatic foliar fungi that colonize Acer macrophyllum alter litter decomposition rates in a freshwater stream and how their presence affects realized microbial community composition, through culture-independent work.
Results/Conclusions
In the A. macrophyllum study, the presence of the two symptomatic foliar fungi significantly increased litter decomposition rates and decreased fungal spore production. Additionally, these fungi had a significant effect on realized bacterial community composition in a freshwater habitat. These results suggest that stochastic colonization processes of foliar fungi can lead to priority effects following host leaf senescence, thereby altering rates of nutrient cycling and litter microbial community composition. Further, we discuss the implications of altered litter decomposition rates in the Catenasporaceae-fern symbiosis and how this affects host fitness. Specifically, prolonged litter decomposition may be an unexplored mechanism that plants exploit to reduce competition from neighboring plants when senescent foliar tissue remains attached for several years. Preliminary work suggests that a newly-discovered mutualism exists between fern hosts and Catenasporaceae in which the host strongly filters fungal colonists, providing a niche for this family of fungi to undergo sexual reproduction and host recolonization, all while prolonging litter decomposition to the benefit of the fern. We argue that the modification of litter decomposition should be examined as a standard phenotype of fungal endophytes as it may greatly impact both nutrient cycling and host fitness.