Dovetailing the Genetic, Developmental and Functional Bases of the Adaptation of Stomatal Traits to Climate

Stomata, the micro‐valves on leaves, regulate CO 2 uptake and water loss. Thus, the anatomical maximum stomatal conductance, g max , is a key influence on gas exchange, growth and productivity. For 145 geographically diverse ecotypes of Arabidopsis thaliana grown in a common garden we tested hypotheses for the drivers of variation in g max and a stomatal size‐density trade‐off, considering epidermal optimization, epidermal development and climate adaptation. Ecotypes native to colder and drier macroclimates had higher g max , consistent with leaf‐scale stress‐avoidance, despite having longer times to flowering. A high g max was achieved through greater epidermal allocation to stomata, via both increased guard cell initiation and smaller epidermal pavement cells. Stomatal traits showed polygenic associations with climate. A weak stomatal size‐density trade‐off was observed for only the abaxial surface, consistent with flexible constraints on stomatal development and independent trait adaptation. Dovetailing mechanisms influence stomatal adaptation to climate across a wide‐ranging species.