Many legumes (family Fabaceae) are dependent on symbiosis with nitrogen-fixing bacteria (rhizobia) for growth and reproduction, a trait evolved from a single origin almost 60 million years ago. The extent to which this microbial symbiosis either promotes or impeeds plant distribution is unknown.
In this study, researchers investigated and compared non-native establishment patterns of 3,500 species of symbiotic and non-symbiotic legumes. Relying on GBIF-mediated occurrences, the researchers verified legume range data from the International Legume Database and Information Service (ILDIS). By applying the nitrogen-fixation status of each species, their data revealed a significantly lower probability of symbiotic legumes occurring in non-native regions, suggesting symbiosis as a limiting factor. The authors point to lack of compatible bacterial species or inappropriate environmental conditions for nitrogen fixation as likely explanations.
While other factors (e.g latitude of origin, woodiness and human uses) also appeared important, their effects did not eliminate symbiosis as a key determinant of establishment in novel ranges. The study highlights the importance of mutualisms and other species interactions in predicting species invasiveness.