Aim Recent research has highlighted that the relationship between species interactions and latitude can differ between native and invasive plant taxa, generating biogeographical heterogeneity in community resistance to plant invasions. In the first study with foliar pathogens, we tested whether co-occurring native and invasive lineages of Phragmites australis exhibit nonparallel latitudinal gradients in foliar fungi communities, pathogen susceptibility and damage, and whether these biogeographic patterns can influence invasion success.
Location North America.
Time period 2015-2017.
Major taxa studied Perennial grass Phragmites australis.
Methods We surveyed 35 P. australis field populations, spanning 17° latitude and comprising four phylogeographic lineages, including one endemic to North America and one invasive from Europe. For each population, we quantified percent leaf pathogen damage and cultured fungi from diseased leaves, that we identified using molecular tools. To assess whether latitudinal gradients in pathogen damage were genetically-based, we inoculated plants from 73 populations with four putative pathogens in a complementary common garden experiment, and measured P. australis susceptibility (i.e., diseased leaf area).
Results We isolated 84 foliar fungi morphospecies. Phragmites australis lineage correlated with fungal community composition but not abundance, richness or diversity. Despite the invasive European P. australis lineage being the least susceptible to three of the four pathogens tested in the common garden experiment, pathogen damage in the field was similar between native and invasive lineages, providing no evidence that release from foliar pathogens contributes to invasion success. Regardless of lineage, pathogen damage in the field was threefold higher for northern than southern populations, where local environmental conditions likely obscured genetically-based gradients in pathogen susceptibility.
Main conclusions Our results highlight that host plant lineage and genetically-based biogeographic gradients strongly influence foliar fungi community structure and pathogen susceptibility, but do not translate to differences in pathogen damage observed in the field.
Keywords: biotic resistance, diversity, endophytes, enemy release, genotype, invasive plant, latitudinal gradients, native plant, plant-fungi interactions, Phragmites australis