Introduction
Invasive plant species are those that spread beyond their native range,
successfully colonizing a great diversity environments (sensuRejmánek et al. 2005). In their new distributional range, invasive
species are often exposed to environmental conditions that can be
different from those in their original geographic range. Their success
may be attributed to rapid ecotypic differentiation (Matesanz et al.
2010, Marchini et al. 2019) and/or adaptive phenotypic plasticity (Geng
et al. 2007, Gentili et al. 2021). Since plant phenotypic plasticity can
be positively modulated by symbiotic microorganisms (Goh et al. 2013,
Petipas et al. 2021), the ability to establish symbiotic associations
with local soil microorganisms may serve as a mechanism of invasive
plants to overcome the novel limitations. Still, populations of an
invasive species, whether from outside or inside the original
distributional range, may differ in their ability to recruit the local
soil microbiota and obtain benefits from it.
Plants associate with soil beneficial microorganisms and the evidence
shows that these symbiotic associations confer several eco-physiological
benefits to hosts, including improved nutrient uptake and increased
tolerance to biotic and abiotic conditions (Acuña‐Rodríguez et al. 2020,
Liu et al. 2020). Soil microorganisms can also play a crucial role in
both plant invasion success as well as expansion of species distribution
range (Reinhart and Callaway 2006, Traveset and Richardson 2014, Dawson
and Schrama 2016, Ramirez et al. 2019). Previous studies have focused on
specific components on the soil microbiome such as pathogens or
mutualists, and how they differentially modulate the performance of
invasive versus native species (Dawson and Schrama 2016, Dickie et al.
2017). For example, Shelby et al. (2016) found little support for the
prediction that the ability of Trifolium plants from the
introduced range (i.e., New Zealand) to establish associations with
beneficial microorganisms (rhizobia and arbuscular mycorrhizal fungi)
from the native-range soil would be limited compared with their native
counterparts. However, since the soil microbiota is made up of complex
communities of bacteria, archaea, and fungi (Hartmann and Six 2023),
plants can still fulfill a versatile range of functions due to
redundancy and complementarity. For example, the invasive Poa
annua exhibited higher competitive ability against the local Antarctic
species Deschampsia antarctica in the presence of root fungal
endophytes, and this effect was related to an endophyte-mediated
increase in the allelopathic compounds in the rhizospheric soil
(Ballesteros et al. 2022). However, few studies have considered how the
importance of the soil microbiome for plant performance can vary among
populations that, within the introduced or the native range, occur in
habitats with contrasting environmental conditions.
In this study, we posit that soil microorganisms may positively
influence traits linked with higher plant performance and invasion
success (i.e., survivorship, plant biomass and flower production) and
predict that their relative significance will be more pronounced
(i ) in invasive than native ranges, and (ii ) locations
with more stressful environmental conditions. To test these predictions,
we conducted two complementary experiments using the widely distributed
species Taraxacum officinale L. (dandelion) as study system.
First, we carried out a cross-transplant experiment to compare the
effects of the soil microbiomes from the native (Europe) and invasive
(South America) ranges on the invasion-related traits of T.
officinale . Second, we compared the relative importance of the soil
microbiome in influencing invasion-related traits in nine populations ofT. officinale distributed along a latitudinal gradient within its
invasive range (South America), which encompasses varying levels of
environmental stress.