Clinal variation in stomatal characteristics of an Arctic sedge, Eriophorum vaginatum (Cyperaceae)

• Premise of the study: In a large reciprocal transplant experiment, Eriophorum vaginatum tussocks transplanted along a latitudinal gradient in Alaska's interior exhibited genetic differentiation and phenotypic plasticity for vegetative traits. Using the same tussocks 30 yr later, we used estimates of growing season temperature at each site to ask whether there was a climatic cline for stomatal density, size, and conductance. • Methods: We created impressions of the abaxial leaf surfaces of the transplanted individuals for viewing under a microscope and measured stomatal density (SD) and length (SL) for 224 individuals. We used SD and SL to estimate stomatal conductance ( C ). Separate one‐way analyses of variance were performed to quantify the effect of population genetic differences and latitudinal environmental variation on stomatal characteristics. • Key results: Our data suggest that stomatal size was influenced by both genetics and environment and that plasticity for stomatal density produced highest densities at the coolest sites. Stomatal conductance increased with decreasing temperature of site from which the populations originated. • Conclusions: Our results demonstrate a cline in stomatal conductance in E. vaginatum , with some ability of populations to plastically produce an appropriate phenotypic response in a new environment. Because the species is a dominant species in many arctic plant communities, its ability to produce an appropriate stomatal phenotype and to optimize water use efficiency by decreasing stomatal conductance in warmer environments could affect both community composition and total primary productivity in future, warmer climates.