DOI: 10.5061/dryad.hdr7sqvdg
title: Patterns of plant naturalization show that facultative mycorrhizal plants are more likely to succeed outside their native Eurasian ranges

description: The naturalization of an introduced species is a key stage during the
 invasion process. Therefore, identifying the traits that favor the
 naturalization of non-native species can help understand why some species
 are more successful when introduced to new regions. The ability and the
 requirement of a plant species to form a mutualism with mycorrhizal fungi,
 together with the types of associations formed may play a central role in
 the naturalization success of different plant species. To test the
 relationship between plant naturalization success and their mycorrhizal
 associations we analysed a database composed of mycorrhizal status and
 type for 1981 species, covering 155 families and 822 genera of plants from
 Europe and Asia, and matched it with the most comprehensive database of
 naturalized alien species across the world (GloNAF). In mainland regions,
 we found that the number of naturalized regions was highest for
 facultative mycorrhizal, followed by obligate mycorrhizal and lowest for
 non-mycorrhizal plants, suggesting that the ability of forming mycorrhizas
 is an advantage for introduced plants. We considered the following
 mycorrhizal types: arbuscular, ectomycorrhizal, ericoid and orchid
 mycorrhizal plants. Further, dual mycorrhizal species were those that
 included observations of arbuscular mycorrhizas as well as observations of
 ectomycorrhizas. Naturalization success (based on the number of
 naturalized regions) was highest for arbuscular mycorrhizal and dual
 mycorrhizal plants, which may be related to the low host specificity of
 arbuscular mycorrhizal fungi and the consequent high availability of
 arbuscular mycorrhizal fungal partners. However, these patterns of
 naturalization success were erased in islands, suggesting that the ability
 to form mycorrhizas may not be an advantage for establishing
 self-sustaining populations in isolated regions. Taken together our
 results show that mycorrhizal status and type play a central role in the
 naturalization process of introduced plants in many regions, but that
 their effect is modulated by other factors.
description: We compiled information on
 mycorrhizal status and mycorrhizal type from different sources: a database
 on mycorrhizal occurrence on vascular plant species across eastern Europe
 and north Asia (Akhmetzhanova et al. 2012), a database on mycorrhizal
 associations for plant species in central Europe (Hempel et al. 2013), a
 database on mycorrhizal associations for plants across Europe (Bueno et
 al. 2017) and a database on mycorrhizal occurrence on vascular plants from
 Europe and north Asia (Correia et al. 2018). We checked entries in several
 databases and their cited references to minimize errors. We included three
 mycorrhizal statuses: non-mycorrhizal, obligate mycorrhizal and
 facultative mycorrhizal. We classified each plant species into one
 mycorrhizal status according to observations of mycorrhizal associations
 (or the absence of mycorrhizal associations) directly on plant roots, at
 the individual plant level, following an approach repeatedly used in
 previous studies (Hempel et al. 2013, Bueno et al. 2017, Menzel et al.
 2017, Correia et al. 2018). Non-mycorrhizal species were those that
 included only observations (on individual plants) of absence of
 mycorrhizal associations, and obligate mycorrhizal species were those that
 included only observations of mycorrhizal associations. Facultative
 species were those that included observations of mycorrhizal associations
 (either with arbuscular mycorrhizal or ectomycorrhizal fungi) as well as
 observations of absence of mycorrhizal associations. We considered a
 minimum of two independent observations for each mycorrhizal status
 (mycorrhizal associations and absence of mycorrhizal associations) to
 classify a species as facultative mycorrhizal in order to reduce the
 influence of observer errors. The number of species with observations of
 facultative ericoid mycorrhizal associations or facultative orchid
 mycorrhizal associations was too low to consider them in our analyses. It
 is important to note that these three mycorrhizal categories only indicate
 observed root colonization status and do not include information about
 functionality, such as mycorrhizal dependence. There were some cases of
 conflicting databases, which were caused by Correia et al. (2018) not
 including facultative ectomycorrhizal and dual mycorrhizal categories. In
 this regard, Correia et al. (2018) considered as obligate ectomycorrhizal
 plants those with observations of this mycorrhizal type, without any
 regard on facultative ectomycorrhizal species (ectomycorrhizal -
 non-mycorrhizal) or dual mycorrhizal species (arbuscular -
 ectomycorrhizal). Therefore, we checked every plant species classified as
 obligate ectomycorrhizal according to Correia et al. (2018) in their
 original data source and in other mycorrhizal databases to evaluate if any
 plant species was originally classified as facultative ectomycorrhizal or
 as dual mycorrhizal. We considered
 five mycorrhizal types within the obligate mycorrhizal status: arbuscular
 mycorrhizal, ectomycorrhizal, ericoid mycorrhizal, orchid mycorrhizal and
 dual mycorrhizal (Smith and Read 2008, Moora 2014, Correia et al. 2018).
 Dual mycorrhizal species were those that included observations of
 arbuscular mycorrhizas as well as observations of ectomycorrhizas (at
 least two independent observations of each mycorrhizal type). The number
 of plant species with observations of dual mycorrhizal associations
 involving either ericoid or orchid mycorrhizal types was too low to
 consider them in our analyses. We standardized species names according to
 The Plant List (www.theplantlist.org) using the TPL function from the
 “taxonstand” package (Cayuela et al. 2012)                  We use data on
 naturalization of vascular plant species from the GloNAF database version
 1.2 (van Kleunen et al. 2019). The GloNAF database is the most
 comprehensive data source on naturalized vascular alien plant species.
 This database includes information of 13,939 taxa and 1029 regions, based
 on 210 data sources (van Kleunen et al. 2019). A region is defined here as
 the smallest geographic area for which a list of alien plant species is
 available. From the total number of regions a subset of 648 are considered
 as mainland regions and a subset of 381 as island regions. Both mainland
 and island regions vary widely in their surface area. Species names in the
 GloNAF database are already standardized according to The Plant List. We
 merged our database on mycorrhizal status and type with the GloNAF
 database. From the 3719 species in our mycorrhizal database 1981 were
 recorded as naturalized in at least one region according to the GloNAF
 database. For these 1981 species we calculated naturalization success as
 the number of regions where each species is reported to be naturalized.
 This would be an indicator of the tendency to spread, or invasiveness, of
 a plant species belonging to a particular group. We also calculated
 naturalization success as the area where each species is naturalized
 (adding up the areas of all the regions where the species is reported to
 be naturalized) to evaluate if we obtained the same patterns of
 naturalization success.   References Akhmetzhanova,
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