It is still debated whether alien plants benefit from being mycorrhizal, or if engaging in the symbiosis constrains their establishment and spread in new regions. We analyzed the association between mycorrhizal status of alien plant species in Germany and their invasion success. We compared whether the representation of species with different mycorrhizal status (obligate, facultative, or non-mycorrhizal) differed at several stages of the invasion process. We used generalized linear models to explain the occupied geographical range of alien plants, incorporating interactions of mycorrhizal status with plant traits related to morphology, reproduction, and life-history. Non-naturalized aliens did not differ from naturalized aliens in the relative frequency of different mycorrhizal status categories. Mycorrhizal status significantly explained the occupied range of alien plants; with facultative mycorrhizal species inhabiting a larger range than non-mycorrhizal aliens and obligate mycorrhizal plant species taking an intermediate position. Aliens with storage organs, shoot metamorphoses, or specialized structures promoting vegetative dispersal occupied a larger range when being facultative mycorrhizal. We conclude that being mycorrhizal is important for the persistence of aliens in Germany and constitutes an advantage compared to being non-mycorrhizal. Being facultative mycorrhizal seems to be especially advantageous for successful spread, as the flexibility of this mycorrhizal status may enable plants to use a broader set of ecological strategies.

Berlin Brandenburg Institute of Advanced Biodiversity Research 14195 Berlin Germany

Department of Botany and Zoology Centre for Invasion Biology Stellenbosch University Matieland 7602 South Africa

Department of Community Ecology Helmholtz Centre for Environmental Research UFZ Theodor Lieser Strasse 4 06120 Halle Germany

Department of Ecology Faculty of Science Charles University Viničná 7 CZ 128 44 Prague 2 Czech Republic

Department of Invasion Ecology Institute of Botany The Czech Academy of Sciences CZ 252 43 Průhonice Czech Republic

German Centre for Integrative Biodiversity Research Halle Jena Leipzig Deutscher Platz 5e 04103 Leipzig Germany

Institute of Biology Dahlem Center for Plant Sciences Freie Universität Berlin Altensteinstraße 6 14195 Berlin Germany

Institute of Biology Geobotany and Botanical Garden Martin Luther University Halle Wittenberg Am Kirchtor 1 06108 Halle Germany

Institute of Ecology and Earth Sciences University of Tartu 40 Lai Street Tartu 51005 Estonia

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Arbuscular mycorrhizal fungi favor invasive Echinops sphaerocephalus when grown in competition with native Inula conyzae