Guard cell and subsidiary cell sizes are key determinants for stomatal kinetics and drought adaptation in cereal crops.

Summary: Climate change‐induced drought is a major threat to agriculture. C4 crops have a higher water use efficiency (WUE) and better adaptability to drought than C3 crops due to their smaller stomatal morphology and faster response. However, our understanding of stomatal behaviours in both C3 and C4 Poaceae crops is limited by knowledge gaps in physical traits of guard cell (GC) and subsidiary cell (SC).We employed infrared gas exchange analysis and a stomatal assay to explore the relationship between GC/SC sizes and stomatal kinetics across diverse drought conditions in two C3 (wheat and barley) and three C4 (maize, sorghum and foxtail millet) upland Poaceae crops. Through statistical analyses, we proposed a GCSC‐τ model to demonstrate how morphological differences affect stomatal kinetics in C4 Poaceae crops.Our findings reveal that morphological variations specifically correlate with stomatal kinetics in C4 Poaceae crops, but not in C3 ones. Subsequent modelling and experimental validation provide further evidence that GC/SC sizes significantly impact stomatal kinetics, which affects stomatal responses to different drought conditions and thereby WUE in C4 Poaceae crops.These findings emphasize the crucial advantage of GC/SC morphological characteristics and stomatal kinetics for the drought adaptability of C4 Poaceae crops, highlighting their potential as future climate‐resilient crops. [ABSTRACT FROM AUTHOR]