Interspecific trait differences drive plant community responses on serpentine soils.

Serpentine ecosystems are characterised by multiple environmental
stressors: high levels of trace metals such as nickel (Ni), low
availability of macronutrients and low water retention. These harsh
environmental conditions exert a strong selective force on the vegetation,
but their effect on community assembly processes and the functional trait
composition remains unknown. In 26 plots on four serpentine sites on
Lesbos Island (Greece), we measured six leaf functional traits related to
resource acquisition and stress resistance on the 20 most abundant plant
species. We quantified the proportion of variance explained by inter- and
intraspecific traits difference and tested if individual species show
changes in trait values explained by soil Ni content. We investigated the
adaptive value and the community level changes for each trait along the
natural soil Ni gradient using a mixed model approach and functional
diversity analyses. We also tested the role of the abundant serpentine
endemic and Ni-hyperaccumulating species Odontarrhena lesbiaca in
driving these patterns. Intraspecific variation explained by soil Ni
content is smaller than 4%, and most of the variance is explained by
interspecific differences in trait values. Most species do not show
significant changes in trait values in response to soil Ni. At the
community level, low specific leaf area and small and thick leaves are
selected on high Ni soils. Functional diversity analyses suggest a shift
towards a stress tolerance syndrome (thick and small leaves with low SLA
values), and an increase in functional diversity on Ni rich soils.
However, these patterns are driven by the increasing abundance
of O. lesbiaca. The endemic Ni hyperaccumulator has a stress
tolerance strategy with small thick leaves and low SLA, while the
community of broadly distributed species show an increase in trait values
related to dominance and fast growth. Synthesis. Intraspecific variation
in leaf trait responds little to soil metal toxicity. Endemic species
harbour unique trait values compared to species with broad distribution
which should justify their conservation as a priority.