Strong effect of soil and weak climate signal on edaphic island
plant persistence
The studied edaphic islands associated with rocky outcrops are
distinguished by shallow soils with high sand content, low water
retention capacity and low nutrient availability. These harsh edaphic
conditions contributed greatly to shaping the non-acquisitive trait
patterns influencing the local persistence of perennial plant species.
The evidence that soil properties operate as one of the key drivers of
persistence strategies edaphic of island plants aligns with other
studies (Kazakou et al., 2008; Spasojevic et al., 2014; Hulshof &
Spasojevic, 2020). Increasing variability in soil depth was consistently
related to higher BDMC values across all clonal species, suggesting that
fine-scale soil heterogeneity may push these plants to be more
conservative belowground, i.e. a “stay-where-you-are” adaptive
strategy (Graae et al., 2018).
Non-clonal plants grew better in deeper and sandier soils, while plants
on more fertile soils tended to grow older but at a slower pace, as for
individuals of Carlina and Helianthemum . These findings
challenge the notion that plants inhabiting harsher environments are
slower in their growth and longer-lived (Nobis & Schweingruber, 2013).
This may suggest that Carlina and Helianthemum have
developed at the intraspecific level unique adaptive strategies to
successfully persist in the distinct conditions provided by the edaphic
islands, which do not necessarily constrain their growth (Doležal et
al., 2021). Non-clonal plants also exhibited a greater ability to
transport water through larger vessels in deeper, more variable and
sandier soils. Yet, this may be explained by an adaptive hydraulic
safety-efficiency functional trade-off (Drake et al., 2015). Larger
vessels may imply quicker growth (as found for Helianthemum,probably facilitated by its deep rooting ability; Doležal et al., 2021)
and higher evapotranspiration, but may also increase the risk of
embolism associated with cold and arid spells typical of the
highly-seasonal temperate dry grasslands.
Climate affected only a few traits, often showing inconsistent patterns.
This flags a minor role of climate in shaping the persistence strategies
of edaphic island plants compared to soil properties and insularity. The
macroclimate can be considered the same across all the edaphic islands.
Yet, microclimate (captured by the data-loggers) can differ within
single islands because of variable slope aspect, inclination and solar
radiation generated by the rugged terrain and dome-shaped topography of
the outcrops (de Paula et al., 2019; Ottaviani et al., 2016). Still, for
clonal species, we identified that warmer climates and reduced
temperature fluctuations affected plant height negatively and BDMC
positively. This result points towards more conservative resource
economics under warmer conditions and may indicate that with the
anticipated and exacerbating warming of the region, clonal species may
be able to cope with these changes (Saar et al., 2012). For non-clonal
species, results were even scantier and not pointing towards any
generalizable trend.