Interspecific trait differences drive plant community responses on serpentine soils

Serpentine ecosystems are characterized by multiple environmental stressors such as 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 the functional trait composition of the communities 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 selective value and the community level changes for each trait along the natural soil Ni gradient using a species multilevel model approach and functional diversity analyses. We also tested the role of the abundant serpentine endemic Odontarrhena lesbiaca in driving these patterns.

Intraspecific variation explained by soil Ni content is smaller than 2%, with most of the variance being explained by interspecific differences in trait values and most species do not show significant changes in trait values. At the community level, leaf thickness is the only trait driving an increase in species abundance along the gradient. Functional diversity analyses suggest a shift towards a stress tolerance syndrome (thick leaves with low SLA values) on Ni rich soils, but an increase in the diversity of these traits. However, these patterns are driven by the increasing abundance of O. lesbiaca . When this species is excluded, there is an increase in the community mean leaf area and SLA, suggesting that the community does not respond to metallic stress with classical stress syndromes.