Patterns of phenotypic plasticity along a thermal gradient differ by trait type in an alpine plant

Climate change presents many challenges for plants, a major one of which is the steady increase in the temperatures that plants are exposed to during germination, growth and reproduction. Generating a more complete understanding of the capacity for plants to respond and of the role that phenotypic plasticity plays in facilitating species' responses to warming temperatures is a central objective in global change ecology. Different traits expressed across life stages might be expected to exhibit a variety of responses to temperature due to phenotypic plasticity and genetic variation, even within a species. However, the extent of the variation among trait types and the relative contribution of plasticity and genetics to responses along a thermal gradient are not well understood. Here, we studied an alpine plant, Wahlenbergia ceracea, to determine the shapes of plastic responses in 14 traits across germination, leaf, physiology and reproductive fitness trait types across a broad thermal gradient of temperatures while also comparing responses among family lines. Trait types differed markedly: germination, leaf and reproductive traits showed nonlinear plasticity with best performance at intermediate temperatures, whereas physiology traits were generally less responsive to temperature. Variation in plasticity among families was lowest for the traits most necessary for tolerating environmental extremes (e.g. heat tolerance), suggesting that physiology traits may be canalised and fitness suffers for it. In contrast, variation in means, and plasticity in some cases, among families in germination traits suggests genetic variation and hence the potential for these few traits to respond to selection. Our results illustrate the variety of responses that may occur in response to temperature, and the frequent occurrence of complex nonlinear plastic responses that would not have been apparent with comparison of fewer temperatures. We discuss the physiological, ecological and evolutionary insights our findings provide into the response of wild species to the changing climate. Read the free Plain Language Summary for this article on the Journal blog.