Leaf stomatal density changes in response to water availability, affecting photosynthesis in grass. Moderate water deficits increase stomatal number, but severe deficits decrease it. Stomatal size decreases with water deficit. Stomatal density is linked to gas exchange rates and water use efficiency. A negative correlation exists between stomatal density and leaf area, suggesting a balance between them. Stomatal density and guard cell size are flexible and change with water availability, impacting photosynthesis and water use efficiency.