Plant Physiology & Development
Stomatal Conductance & Gas Exchange
Stomata regulate the exchange of carbon dioxide and water vapor between the leaf and atmosphere. Their behavior responds to light, internal carbon dioxide, water status, vapor-pressure conditions, hormones, temperature, and other signals.
Key concepts
- Carbon dioxide entry and water-vapor loss are coupled through stomatal pores
- Stomatal conductance is not the same as photosynthetic rate
- High atmospheric demand can increase transpiration pressure while also promoting stomatal restriction if plant water supply cannot keep pace
- Leaf temperature and boundary-layer conditions change gas-exchange behavior
- Root-zone stress can alter stomatal behavior before dramatic visual symptoms appear
What to measure or observe
- Record air temperature, RH, leaf temperature, and light context together
- Compare leaf posture and temperature across canopy zones
- Observe recovery after irrigation or environmental transitions
- Use gas-exchange instruments when quantitative stomatal conductance is required
- Track root-zone moisture and EC alongside atmospheric measurements
Common mistakes
- Treating a VPD number as a direct measurement of stomatal conductance
- Assuming open stomata always mean optimal photosynthesis
- Ignoring leaf temperature when interpreting atmospheric demand
- Changing humidity without considering root water supply
- Diagnosing stomatal behavior from leaf curl alone
Visuals this lesson still needs
- Stomatal pore gas-exchange cutaway
- CO2-in water-vapor-out diagram
- Atmosphere-root coupling map
- Leaf-temperature and boundary-layer graphic