Fungi from a non-native invasive plant increase its growth but have different growth effects on native plants

Non-native invasive plants can associate with and accumulate microbes in their introduced range, which may transfer to native plants and potentially exert pathogenic effects. In these cases, the invasive plant can act as a pathogen reservoir. However, little is known about this as a possible plant invasion mechanism. We isolated fungi from the roots of 32 Vincetoxicum rossicum (Apocynaceae) plants collected across Ontario, Canada, where it is highly invasive. The growth effects of known pathogenic fungi were tested on V. rossicum and two commonly co-occurring native plants, Asclepias syriaca (Apocynaceae) and Solidago canadensis (Asteraceae). We hypothesised that these fungi would reduce the growth of native plants more than that of V. rossicum. Of the18 fungal taxa isolated from V. rossicum roots, 15 were previously reported as pathogens on other plants and 16 represent new records on this plant. Four of the seven fungi tested on V. rossicum increased its total biomass and/or root-shoot ratio compared to uninoculated controls. When inoculated individually, three of these fungi had neutral growth effects on the native plants. However, when inoculated together, Cadophora sp., Ilyonectria radicicola, and Macrophomina phaseolina reduced the total biomass of S. canadensis. These results support that at least in some cases non-native invaders may benefit from associating with soil microbes that can function as pathogens on native plants. These differential functional outcomes between non-native invasive and native plants may be important for mediating plant community structure and the persistence of invasive plants.