Studies assessing the rates at which plant species ranges have shifted in response to recent climate change have evidenced large variations in responses across species. This individualistic nature of migration has been explained by interspecific (i.e., between-species) differences in tolerance of various climate variables. But climate conditions also have been associated with considerable local adaptations within species (i.e., intraspecific variability), which could complicate projections of species range shifts in response to climate change. We used a common garden approach in controlled-environment growth chambers to investigate potential local adaptations in growth (height, biomass) and physiological (gas-exchange) responses to warming of Solidago caesia (blue-stemmed goldenrod) and Carex aestivalis (summer sedge) propagated from field-sampled populations along a latitudinal temperature gradient across their ranges in the Appalachian region. Specifically, individuals were grown from seed collected from northern and southern populations in conditions that replicated current and future projected temperatures throughout the sampled range of these species. We used two-way analysis of variance (ANOVA) to test for the main and interactive effects of location of origin with temperature on growth and physiological variables to assess the role of local adaptation in responses to warming.
Results/Conclusions
Across temperature levels, individuals from the southern S. caesia and C. aestivalis populations were characterized by significantly earlier germination and increased growth than individuals from northern populations. Southern individuals of S. caesia also exhibited significantly greater rates of instantaneous leaf-level photosynthesis than their northern counterparts. Temperature was associated negatively with growth in S. caesia and positively with growth in C. aestivalis when considered across locations of origin, but physiological variables were not significantly influenced by temperature as a main effect. Significant interactions of location of origin and temperature revealed southern S. caesia and C. aestivalis individuals generally responded negatively to warming when compared between current and future conditions, while northern populations exhibited neutral or positive responses to warming. Although limited, these results suggest that populations of these species already near their high temperature range limit could respond negatively to future warming, but that populations near cold range limits may persist. More generally, our results evidence the potential key role that local adaptations may play in our ability to make predictions about future plant species ranges. Ongoing expansions of our research that include additional populations, species, measures, and modeling efforts aim to enhance our capabilities to make such predictions.