Variable effects on growth and defence traits for plant ecotypic differentiation and phenotypic plasticity along elevation gradients

Along ecological gradients, phenotypic differentiation can arise through natural selection on trait diversity and magnitude, and environment-driven plastic changes. The magnitude of ecotypic differentiation versus phenotypic plasticity can vary depending on the traits under study. Using reciprocal transplant-common gardens along steep elevation gradients, we evaluated patterns of ecotypic differentiation and phenotypic plasticity of several growth and defence-related traits for two coexisting but unrelated plant species, Cardamine pratensis and Plantago major. For both species, we observed ecotypic differentiation accompanied by plasticity in growth related traits. Plants grew faster and produced more biomass when placed at low elevation. In contrast, we observed fixed ecotypic differentiation for defence and resistance traits. Generally, low elevation ecotypes produced higher chemical defences regardless of the growing elevation. Yet, some plasticity was observed for specific compounds...