Native and exotic grasses share generalist foliar fungi in a Canterbury high country grassland

Communities of foliar fungal pathogens and endophytes can influence the success and impacts of exotic plants. A key unresolved question concerns how these foliar fungal communities are structured, including whether they systematically differ between native and exotic plants, or are influenced by plant phylogeny and host abundance. To address these questions, we used culturing and Sanger sequencing to characterise the culturable foliar fungal communities of three native and seven exotic grass species that co-occurred in a high-country grassland in Canterbury, Aotearoa New Zealand. We tested the following predictions: Diversity and community composition of culturable foliar fungi differs (1) between native and exotic grass species, (2) between common and rare grass species, and (3) more closely related grass species host more similar fungal communities. We identified 39 fungal operational taxonomic units (OTUs) from 201 isolates. Overall, native and exotic grass species did not differ in their foliar fungal diversity, community composition, or the relative isolation frequency (i.e. abundance) of potential pathogens. However, native grasses hosted a higher proportion of foliar fungi that were isolated from only one host species than exotics (i.e. rare or specialist fungi), possibly due to their longer coevolutionary history with resident fungi. Common grass species (three exotics and two natives) also hosted more fungi that were isolated from only one host species than rare grasses, potentially driven by their greater connectivity and reduced dispersal limitation of foliar fungi. Closely related grass species did not host more similar fungal communities, indicating that host species phylogeny was not a useful predictor of foliar fungal community structure in this high-country grassland. Taken together, our results suggest that exotic grasses have integrated into the resident community via generalist foliar fungi and do not escape from foliar fungal pathogens, with potential for indirect impacts of exotics on co-occurring native plants.