Clonal and non-clonal edaphic island plants have different
persistence strategies
Except for plant height and BDMC, we assessed different traits for
clonal and non-clonal species, mainly because i) collecting anatomical
traits for clonal plants is challenging and destructive (the oldest part
of the rhizome is necessary but often out-of-reach or decomposed), and
ii) some traits may be measured only for one group, such as lateral
spread for clonal plants (Klimešová et al., 2019). Yet, all the traits
included in this study capture different dimensions associated with
non-acquisitive functions shaping species persistence strategies. These
are: 1) resource conservation represented by BDMC and storage tissue, 2)
plant growth associated with plant height, lateral spread, radial
growth, and vessel size, and 3) plant lifespan linked to plant age. Not
all traits, however, proved to have the same responsiveness. BDMC
emerged as the most responsive and consistent trait across species,
especially for clonal plants – the only case where the considerable
portion of the explained variability in the model was attributable to
predictors only (and no effect of species identity was detected; Table
2). This trait is the belowground coarse organ parallel to LDMC and
mainly linked to resource conservation function and carbohydrate
storage. BDMC can provide insights also into plant ability to
overwinter, store water, and multiply clonally – similarly to LDMC
reflecting leaf longevity (de Bello et al., 2012; Pérez-Harguindeguy et
al., 2013). The functional significance of BDMC and its relationship
with other traits would deserve further investigation in different
ecological contexts; BDMC may serve as an easy surrogate for other
belowground traits and functions that are more laborious to gather data
for.
By treating clonal and non-clonal species separately, we were able to
detect similarities as well as differences within and among perennial
species forming temperate dry grasslands. Clonal species, capable of
both vegetative and sexual reproduction, exhibited consistently similar
trait responses to variations in environmental conditions and
insularity. In temperate grasslands, clonal species tend to prefer moist
and nutrient-rich environments (Klimešová et al., 2016b, 2018).
Therefore, clonal plants specialized to the dry, sandy, shallow-soil and
nutrient-poor environments of isolated rocky outcrops may occupy one of
the limits of their ecological niche in the temperate grassland biome.
Clonal species may avoid local extinction by extending their longevity
through low-cost resource economics (Klimešová et al., 2016a) linked to
higher dry matter content of the belowground organ. We cannot, however,
fully support this conclusion by direct age determination because for
clonal plants, we lack direct measures. Yet, from demographical studies,
we know that these species can largely exceed the lifespan of non-clonal
plants (Janovský & Herben, 2020), and may persist in remnant
populations (Jiménez-Alfaro et al., 2016; Marini et al., 2012; Saar et
al., 2012).
A very different scenario emerged for non-clonal species instead. Half
of the species (Carlina , Helianthemum, Lychnis,
Scleranthus ) were highly responsive to variation in environmental and
insularity conditions. Yet, only in few instances trait responses were
consistent across species. Conversely, the other half of the species,
especially Silene and Thymus , remained almost unaffected
by marked variations in the edaphic status, climate or insularity. Also,
trait responses (or lack thereof) did not mirror plant functional type
either. For example, the chamaephytes Helianthemum andThymus or the forbs Carlina , Centaurea ,Knautia and Scleranthus were distinguished by
well-differentiated strategies to successfully persist on the edaphic
islands (Figure 2b). This may be due to differences in rooting depth and
regenerative strategies (Rosbakh & Poschlod, 2021) and not to plant
longevity (see also Doležal et al., 2021). Such a complex and
species-specific set of responses may indicate that the focal non-clonal
species are likely to be well-adapted to cope with (and not limited by)
the distinct ecological and biogeographical conditions provided by the
spatially-confined temperate dry grasslands. This inference seems
further supported by the almost complete segregation of non-clonal
species niches in the multifunctional space identified by
non-acquisitive persistence-related traits (Figure 2).