4. Discussion
Human activities are profoundly reshaping the Earth to the point that
scientists proposed to define a new geological epoch, the Anthropocene
(Lewis & Maslin, 2015). The continuous global emission of highly toxic
pollutants taking place during this epoch (Vallack & Rypdal, 2019),
challenges the capacity of plants to respond to the rapid shifts in
environmental conditions. Organisms can accommodate to challenging
environmental conditions through phenotypic plasticity (Bradshaw, 2006;
Nicotra et al., 2010), i.e. the ability of a single genotype to express
different phenotypes under diverse environmental conditions (Bradshaw
1965, 2006; Kelly, Panhuis, & Stoehr, 2012; Schlichting, 1986; Sultan,
1987, 2000). Indeed, a now classic expectation is that plasticity of
functional traits may contribute to the survival of plants in highly
heterogeneous environments and changing environmental conditions (e.g.
Henn et al., 2018; Lázaro-Nogal et al., 2015; McIntyre & Strauss, 2014;
Richards et al. 2010;), particularly in clonal plants or during the
invasion of new habitats where genetic diversity can be limited (e.g.
Drenovsky et al., 2012; Geng et al. 2007; Richards, Bossdorf, Muth,
Gurevitch, & Pigliucci, 2006; Richards et al., 2008; Turner, Fréville,
& Rieseberg, 2015; Williams, Mack, & Black, 1995). Hence, plasticity
could be a critical component of population and, ultimately, species
persistence under the current context of global change (Nicotra et al.
2010; Parmesan & Hanley 2015).
In order to understand whether phenotypic plasticity contributes to
individual, population and/or species survival, we need to better
understand the levels of phenotypic variation in response to specific
environmental drivers in different plant taxa (Arnold, Kruuk, &
Nicotra, 2019; Nicotra et al. 2010; Parmesan & Hanley 2015). In this
context, we investigate the patterns of intraspecific variation for
heavy metal accumulation and tolerance in two bryophyte species with
contrasting affinity for heavy metals and discuss the mechanistic basis
for such differences. The present investigation adds to current
knowledge on the extent and patterns of phenotypic variation in a group
of plants highly tolerant to environmental stress but whose response
mechanisms are relatively understudied.