Stomata are tiny pores on the surface of plant leaves and play a central role in global water and carbon cycles. The pores cover less than 5% of the leaf area but facilitate the majority of the exchange of gases between the atmosphere and terrestrial vegetation. The opening of stomata is adjusted to provide CO₂ for photosynthesis and to limit water loss. This process exhibits transient responses under fluctuating environmental conditions. The speed at which stomata respond influences productivity and water use efficiency of both crops and natural ecosystems. Although stomatal responses are a target for crop improvement, we lack a clear description of the process, impeding its complete mechanistic understanding. Novel temporal 3D imaging can address the need for a better description of stomatal movements. By complementing fast high-resolution X-ray microcomputed tomography (μCT) with fluorescence microscopy, we will provide in vivo 3D imaging of variations in epidermal cell size and shape and its effects on stomatal movements, scaling from subcellular to whole leaf traits. To fully harness the high volume of data generated by μCT, we will develop novel computational methods to automatically segment images and track single 3D cells over time. This project will answer long-standing questions about stomatal movements and will generate basic knowledge on how to improve stomatal responses under dynamic environments in order to increase net productivity and water-use efficiency.