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Climate change is simultaneously increasing carbon dioxide concentrations ([CO₂]) and temperature. These factors could interact to influence plant physiology and performance. Alternatively, increased [CO₂] may offset costs associated with elevated temperatures. Furthermore, the interaction between elevated temperature and [CO₂] may differentially affect populations from along an elevational gradient and disrupt local adaptation.

We conducted a multifactorial growth chamber experiment to examine the interactive effects of temperature and [CO₂] on fitness and ecophysiology of diverse accessions ofBoechera stricta(Brassicaceae) sourced from a broad elevational gradient in Colorado. We tested whether increased [CO₂] would enhance photosynthesis across accessions, and whether warmer conditions would depress the fitness of high‐elevation accessions owing to steep reductions in temperature with increasing elevation in this system. Elevational clines in [CO₂] are not as evident, making it challenging to predict how locally adapted ecotypes will respond to elevated [CO₂].

This experiment revealed that elevated [CO₂] increased photosynthesis and intrinsic water use efficiency across all accessions. However, these instantaneous responses to treatments did not translate to changes in fitness. Instead, increased temperatures reduced the probability of reproduction for all accessions. Elevated [CO₂] and increased temperatures interacted to shift the adaptive landscape, favoring lower elevation accessions for the probability of survival and fecundity.

Our results suggest that elevated temperatures and [CO₂] associated with climate change could have severe negative consequences, especially for high‐elevation populations.

 

Abstract Individuals within natural populations can experience very different abiotic and biotic conditions across small spatial scales owing to microtopography and other micro-environmental gradients. Ecological and evolutionary studies often ignore the effects of micro-environment on plant population and community dynamics. Here, we explore the extent to which fine-grained variation in abiotic and biotic conditions contributes to within-population variation in trait expression and genetic diversity in natural plant populations. Furthermore, we consider whether benign microhabitats could buffer local populations of some plant species from abiotic stresses imposed by rapid anthropogenic climate change. If microrefugia sustain local populations and communities in the short term, other eco-evolutionary processes, such as gene flow and adaptation, could enhance population stability in the longer term. We caution, however, that local populations may still decline in size as they contract into rare microhabitats and microrefugia. We encourage future research that explicitly examines the role of the micro-environment in maintaining genetic variation within local populations, favouring the evolution of phenotypic plasticity at local scales and enhancing population persistence under global change.