Sensitivity of thermal imaging and infrared thermometry to detect water status changes in Euonymus japonica plants irrigated with saline reclaimed water

• IR thermometry and thermal imaging were validated to obtain canopy temperature.
• Canopy temperature measured at midday was a useful indicator of saline stress.
• Better correlation between gs and Tc on the sunlit side than the shade side.
• Tc and Tc−Ta were the most sensitive indicators of the euonymus water status.

The potential of thermal imaging and infrared thermometry for monitoring the effects of salinity on Euonymus japonica (euonymus) plants was assessed using the following irrigation treatments: Control (electrical conductivity (EC) < 1.2 dS m−1) and reclaimed water, RW (EC ≈ 4 dS m−1). The experiment was conducted for more than eight months in a plastic greenhouse. The diurnal course of canopy temperature (Tc) and the difference between canopy and air temperature (Tc−Ta) for both sunlit and shaded sides was influenced by high concentration of salts in the reclaimed water. The negative relationship between Tc and stomatal conductance (gs) and between Tc−Ta and gs in April was significant during most of the day, but specifically at midday. Regarding the effect of canopy side, better regression coefficients were obtained between Tc and gs, and between Tc−Ta and gs on the sunlit side of the canopy than on the shaded side. However, except for the crop water stress index on the sunlit side of the canopy, few differences during the day were reported for thermal indices. From April onwards, canopy temperatures were higher in RW plants than in the control, indicating the dependence of canopy temperature on salinity. Comparing the sensitivity of discrete (stem water potential and gs) and continuous (Tc and thermal-derived parameters measured by infrared thermometers) indicators of saline stress, it was shown that Tc and Tc−Ta were the most suitable plant-based indicators for precise irrigation scheduling.