Functional traits of both specific alien species and receptive community but not community diversity determined the invasion success under biotic and abiotic conditions

Biodiversity can provide some resistance to alien species in some cases,
but not in others. The observed paradoxical results may be related to
several reasons, including variations in abiotic and/or biotic conditions,
alien species characteristics, and the fact that the species number cannot
adequately reflect native community diversity. A comprehensive study that
incorporates these elements is lacking. We constructed invasion systems
using nine alien plant species and 12 native communities, composed of two
diversity levels (three vs. six species), under different nitrogen (N) and
arbuscular mycorrhiza fungi (AMF) inoculation conditions. We used this
fully crossed factorial experiment, i.e. N (low vs. high) × native
community diversity (three vs. six species) × AMF (with vs. without), to
systematically explore the invasion success in native communities. We
found that the species number of native communities didn’t affect invasion
success under any of the N or AMF conditions. The effects of N enrichment
and AMF inoculation on invasion were not consistent between alien species
and native communities based on their phenotypic plasticity of functional
traits in response to N enrichment and AMF inoculation. Specifically, the
changing of invasion in response to N enrichment and AMF inoculation was
associated with the plasticity of plant height and root mass fraction
(RMF) that reflects the competitiveness for the acquisition of light and
soil resources. Our results that species number did not capture well the
resistance of the native community suggested that the simple expression of
species richness is not realistic to describe the invasion resistance of
the community. Additionally, the association between functional traits of
both alien species and native communities and invasion success suggested
that changes in competitive advantage and resource acquisition strategy
are more important in explaining changes in invasive success in different
N and AMF conditions. Future studies are needed to explore invasion
success by systematically considering the characteristics of invasive
species and the native community, and the specific abiotic and biotic
conditions. Using functional traits may help advance our understanding of
plant invasion in broad circumstances and shed light on a generalized
framework of biological invasion.