Transpiration

Transpiration is water loss from leaves (mainly via stomata). It cools leaves and drives water movement from roots to shoots, supporting nutrient transport.

What drives transpiration

VPD (vapour pressure deficit)

High VPD (hot/dry air) increases demand and is a common trigger for midday stress and stomatal closure.

Radiation + airflow

• Radiation warms leaves and increases demand
• Airflow strips the humid boundary layer, often increasing transpiration

Root supply + salinity

Dry media, poor roots, or high EC reduce uptake — stomata close to protect water status.

Stomatal control

Stomata regulate both transpiration and CO₂ entry. Stress signalling (ABA) promotes closure under drought/salt stress.

Transpiration and nutrition (calcium & boron)

Calcium (and often boron) delivery to fast-growing tissues relies on steady water flow. Big VPD swings and uneven irrigation can increase disorder risk.

• VPD spikes: closure → reduced flow
• Uneven irrigation: stop/start mass flow amplifies issues
• High EC: reduces uptake even if media looks wet

Practical levers

• Climate: manage VPD (venting/humidity/shading strategy)
• Irrigation: align frequency with radiation/VPD; avoid repeated midday dry-downs
• Root zone: oxygenation and drainage; keep roots healthy
• Salinity: keep substrate EC in range; avoid Na/Cl stress