The full understanding of leaf economics that drives plant investment of carbon and nutrients requires including variation in abiotic, but also biotic interactions such as herbivory. We analysed leaf functional traits related to growth, as well as constitutive and inducible direct and indirect defences against herbivores across 15 species of Cardamine (Brassicaeae), that together have colonized the whole elevation gradient of the Alps.
Results/Conclusions
In a phylogenetic comparative framework, we explored the variation of the geometrical shape of plant strategies (i.e. the functional space of growth and defence) across the full abiotic and biotic variation of the elevation gradient. We found that Cardamine species set themselves along; 1) a high elevation syndrome of slow growth-high constitutive defences where climatic conditions are cold and wet and herbivory is rare, 2) a mid-elevation syndrome of high biomass (high competitive abilities)- high nitrogen-low levels of defences in resource-rich forested habitats, and 3) a low elevation syndrome of fast-growth and high inducibility of defences in hot and dry habitats and high herbivore pressure.
We thus argue that ecological gradients shape variation in both biotic and abiotic factors, in turn shaping plant functional spaces to converge into stable plant-growth defence syndromes within each elevation zone.