Widely distributed native and alien plant species differ in arbuscular mycorrhizal associations and related functional trait interactions

It is debated whether alien plants in new environments benefit from being mycorrhizal and whether widely distributed natives and aliens differ in their associations with mycorrhizal fungi. Here, we compared whether species differing in their origin status, i.e. natives, archaeophytes (alien species introduced before the year 1500) and neophytes (introduced after the year 1500), and arbuscular mycorrhizal (AM) status (obligate, facultative, non-mycorrhizal) differ in their area of occupancy in Germany (i.e. number of occupied grid cells, each similar to 130 km(2)). We used generalized linear models, incorporating main effects and up to three-way interactions combining AM status, origin status and plant functional traits. The latter were chosen to describe the possible trade-off in carbon allocation either towards the symbiosis or to other plant structures, such as storage organs (significant interactions involving traits were assumed to indicate the existence of such trade-offs). AM status significantly explained the area of occupancy of natives and neophytes - with facultative mycorrhizal species occupying the largest area in both groups - but was less pronounced among archaeophytes. Archaeophytes may have reduced dependency on AM fungi, as they are generally agricultural weeds and the symbiosis potentially becomes obsolete for plants growing in habitats providing a steady provision of nutrients. Trait interactions between AM status and other functional traits were almost exclusively detected for neophytes. While facultative mycorrhizal neophytes benefit from trade-offs with other traits related to high C cost in terms of area of occupancy, such trade-offs were almost absent among natives. This indicates that natives and neophytes benefit differently from the symbiosis and suggests that native AM fungal partners might be less important for neophytic than for native plant species or that more time is required to establish similar relationships between neophytes and native fungal symbionts.