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| Ecosystems containing multiple nonnative plant species are common, but
mechanisms promoting their co-occurrence are understudied. Plant–soil interactions
contribute to the dominance of singleton species in nonnative ranges because many nonnatives
experience stronger positive feedbacks relative to co-occurring natives. Plant–soil interactions
could impede other nonnatives if an individual nonnative benefits from its soil community to a
greater extent than its neighboring nonnatives, as is seen with natives. However, plant–soil
interactions could promote nonnative co-occurrence if a nonnative accumulates beneficial soil
mutualists that also assist other nonnatives. Here, we use greenhouse and field experiments to
ask whether plant–soil interactions (1) promote the codominance of two common nonnative
shrubs (Ligustrum sinense and Lonicera maackii) and (2) facilitate the invasion of a lesscommon
nonnative shrub (Rhamnus davurica) in deciduous forests of the southeastern United
States. In the greenhouse, we found that two of the nonnatives, L. maackii and R. davurica,
performed better in soils conditioned by nonnative shrubs compared to uninvaded forest soils,
which suggests that positive feedbacks among co-occurring nonnative shrubs can promote
continued invasion of a site. In both greenhouse and field experiments, we found consistent
signals that the codominance of the nonnatives L. sinense and L. maackii may be at least
partially explained by the increased growth of L. sinense in L. maackii soils. Overall, significant
effects of plant–soil interactions on shrub performance indicate that plant–soil interactions
can potentially structure the co-occurrence patterns of these nonnatives. | |
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