Discussion
Our results demonstrate positive effects of soil microbiome on several
plant performance traits for most of the evaluated populations ofT. officinale . However, the soil microbiome appeared to be
particularly relevant for T. officinale plants in the introduced
range, as indicated by its higher impact on plant performance in the
introduce versus native distribution range. Additionally, it played a
more significant role under stressful conditions, as indicated by its
higher influence on plant performance at the extremes of the latitudinal
gradient within the introduced range.
Taraxacum officinale is considered a serious invasive species in
their introduced range due its great environmental tolerance, higher
plasticity and/or ecotypic differentiation (Molina-Montenegro et al.
2012b, 2014). In fact, T. officinale plants from Chilean
populations have shown to possess higher performance than plants from
European populations (Molina-Montenegro et al. 2010, 2011), and to have
negative impacts on local plant communities (Muñoz and Cavieres 2008).
Although previous studies have shown the T. officinale display
several traits related to higher invasive capacity (Pysek and Richardson
2007), none have evaluated whether the soil microbiome can modulate -at
least in part- such traits. For example, accumulating evidence supports
that soil microbiome exerts positive effects on several fitness-related
traits in weeds and invasive species (Trognitz et al. 2016). In
addition, soil microbiome has been suggested to increase growth rate,
improve defense against native herbivores and enhance the competitive
ability of invasive species (Matos et al. 2019, Kalske et al. 2022). In
agreement with these previous findings, we showed that different traits
in T. officinale plants from most of the evaluated populations
were positively affected by soil microbiome. Since the disruption of the
soil microbiome was more severe for the introduced plants, it suggests a
pivotal role for the soil microbiome in the invasion success in the
introduced range.
The level of environmental stress can determine the relative importance
of soil microbiome as a driver of plant performance. In our study, the
soil microbiome had the most positive impact on plants from the northern
and southern populations, with plants from the central populations
showing a lesser effect. Depending on the range of environments they
cover, long latitudinal gradients often exhibit higher levels of abiotic
stress at their extremes (De Frenne et al. 2013). Therefore, the pattern
we observed could be due to an increased dependence on beneficial biotic
interactions as environmental stress increases, as stated by the stress
gradient hypothesis (sensu Betness and Callaway 1994). In our
study, the primary factor contributing to stress differs between the
northern and southern extremes of the latitudinal gradient. In northern
Chile, precipitations are very scarce and temperatures high, while in
the south, temperatures can be extremely low, often dropping below
freezing in winter (Di Castri and Hajek 1976). Although soil
microorganisms are likely to play a crucial role in assisting plants to
cope with water scarcity and high temperatures in the north while with
low temperatures in the south (Acuña‐Rodríguez et al. 2020, Liu et al.
2020), our results showed that the plant performance variables were more
sensitive to environmental conditions in the northern positions of the
latitudinal gradient and to disruptions in the soil microorganism
community. Therefore, soil microorganisms appear to be crucial for the
invasive T. officinale plants to thrive with the dry and warm
environmental conditions.
The soil microbiome can play a critical role in mediating interactions
between native and invasive plant species in a variety of ways. Since
plants recruit the associated soil microbiome from the surrounding soil,
invasive plants could be generalists but able to create a positive
rhizosphere environment, diversifying phenotypes, and functions (Coats
and Rumpho 2014). It is not surprising then, that several hypotheses
that attempt to explain success of plant invasion point out to processes
that occur (or can occur) in the rhizosphere microbiome (enemy release
hypothesis; accumulation of local pathogens, enhanced mutualist
hypothesis, and plant–soil feedback) (see e.g. , Eppinga et al.
2006, Callaway et al. 2008, Blumenthal et al. 2009). Thus, the
biological interactions that result from plants and microorganisms,
either bacteria or fungi, in the rhizosphere soil (whether mutualistic
or pathogenic) are crucial in determining the invasive capacity of plant
species worldwide (Traveset and Richardson 2014, Dickie et al. 2017). In
our study, it is evident that the invasion success of T.
officinale plants in the introduced range could be mediated by a net
positive interaction with soil microorganisms. However, the evidence for
specificity in the effect of soil microorganisms and plants from the
native and introduced range is limited. Rather, our results suggest that
the success of T. officinale is linked to an intrinsic capacity
to recruit microorganisms that exert positive phenotypic effects
associated to increased tolerance on a variety of environmental
conditions.