Effect of air and soil temperature on water balance of jojoba growing under controlled conditions

Jojoba [Simmondsia chinensis (Link) Schneider] cuttings were grown in pots under constant light intensity and vapour pressure deficit at wir temperatures of 18 and 27°C in climate‐controlled cabinets. Leaf conductance and transpiration rate decreased exponentially as the xylen water potential (Ψ_x) decreased concurrently with the drying out of the soil. At high Ψ_x’leaf conductance and transpiration rate were much higher at the higher air temperature, and as Ψ_x declined both parameters decreased more rapidly at 27°C than at 18°C. When soil temperatures were decreased from 27 to 13°C, leaf water potential was not affected at either air temperatures, but transpiration rate was reduced. A linear negative correlation was found between transpiration rates and soil temperatures. It is suggested that the low soil temperature may restrict reducion of water flux in turn reduces stomatal conductance and transpiration without affecting the water potential in the shoot. The releavance of the response to changes in soil or air temperature to the performance of the plant in its semi‐arid habitat is discussed.