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.