Stomata as valves
Guard cells regulate pore aperture controlling CO₂ entry and water vapor loss. Balance between photosynthesis demand and drought stress drives behavior.
Measurement
Infrared gas analyzers measure net photosynthesis and transpiration simultaneously. Calculate intrinsic water use efficiency as A/E ratio.
Environmental drivers
Light, CO₂ concentration, humidity (VPD), and ABA signaling all modulate stomatal opening within minutes.