Invasive ectomycorrhizal fungi species do not grow better in culture than non-invasive species without their hosts

Abstract

Progress has been made in describing invasion patterns of invasive ectomycorrhizal fungi (EMF), yet their ecological characteristics and implications remain poorly understood. Invasive EMF are able to disperse from the initial points of introduction and persist in the soil, generally as spore banks, until their plant hosts invade. The capacity to survive and grow in the absence of a plant host could be a key trait associated with their invasion capacity. While many EMF do not grow in the absence of their hosts, there is a subgroup that can do so in axenic culture. Here we explored the relationship between invasiveness and in-vitro culturability for pine-associated obligate EMF symbionts. We conducted a global literature survey to determine the culturability (culturable/non-culturable) of different EMF species and, when available, their mean growth rates in culture media. We tested the association between in-vitro growth properties and EMF invasiveness (invasive/non-invasive) for 85 EMF species. Surprisingly, we found that EMF culturability (growth without a host in lab conditions) is not associated with their invasiveness, but there are more culture reports for invasive EMF species than for non-invasive species. Vegetative growth rates are not associated with invasiveness either. Mutualistic interactions may be crucial for the success of biological invasions. While for plants, less reliance on mutualists could promote invasions our study sheds light on the ecological characteristics of invasive ectomycorrhizal fungi by suggesting that a relative host autonomy may not be a necessary trait for succeeding as an invasive species.