Local adaptation and plasticity of Erysimum capitatum to altitude: its implications for responses to climate change

1. Alpine plants are at high risk because of climate change. Assessing the performance of alpine plant species across different altitudes is useful for predicting how they may respond to changing climate. Adaptation and plasticity of early life stages are of particular interest since seed germination and seedling establishment could be crucial life-history stages for environmental tracking and population persistence of sexually reproducing plants. 2. To evaluate past adaptation and the potential to accommodate future climate conditions, seeds and seedlings of Erysimum capitatum were reciprocally transplanted between alpine and low-altitude sites. 3. When grown in a common field environment, E. capitatum from alpine and lower-altitude populations differed from each other in germination, size and morphological traits. Planting altitude also influenced those traits, indicating that population differentiation and plasticity to altitudinal conditions both contributed to differences in the performance of highvs. low-altitude plants. Seeds tended to germinate more in their native habitat than in the foreign habitat. Alpine plants survived more than low-altitude plants at high altitude, and they suffered higher mortality when they were planted in low-altitude sites. The production of multiple rosettes, a characteristic morphology of alpine E. capitatum, was negatively associated with survival at low altitude. In contrast to alpine populations, a survival advantage of low-altitude populations in low-altitude sites was not evident in this experiment. 4. Synthesis. Because climate change is projected to cause alpine environments to become more similar to low-altitude environments, alpine Erysimum capitatum is expected to suffer reduced seedling recruitment and higher mortality as a direct response to altered environment and possibly as a result of past adaptation to high altitude. In particular, the production of multiple rosettes, an adaptive trait to the current alpine environment, would constrain plant survival should those environments come to resemble low altitude. Moreover, the limited fitness advantage of low-altitude E. capitatum in low-altitude conditions suggests that environmental tracking by low-altitude populations might have a limited role in maintaining future populations.