Intact Plant Transpiration Measurements. Plants were individually grown on compost in plastic containers in a growth chamber (21°C, 70% relative humidity, 8-h/16-h light/dark, 300 μE·m⁻²·s⁻¹). Each container was closed by a screw cap to avoid evaporation from the compost surface. After sowing, each plant grew through a hole pierced in the middle of the cap. This experimental device ensured that water loss (decrease in weight) could be ascribed to leaf transpiration. Periodic addition of water into the container maintained the compost water content close to 75% (wt/wt). The transpirational water loss was expressed on leaf area basis, estimated from daily plant photographs using OPTIMAS 6.1 software.

A controlled automated growth chamber [Phenopsis robot (28)] was used to impose variable micrometeorological conditions (light and VPD; the containers were weighed every 15 min). To study the effect of Na⁺ on transpiration, the plants were hydroponically grown in half-strength Hoagland solution using the same device (plastic containers) as described above for plants grown on compost. Na⁺ was added to the nutrient solution as a chloride salt.