Usefulness of thermography for plant water stress detection in citrus and persimmon trees

Abstract

The feasibility of using canopy temperature (T c ) measured with a hand-operated infrared thermographic camera as a water stress indicator was evaluated in the field during two seasons on citrus and persimmon trees subjected to different levels of deficit irrigation. In both species, which differ in leaf anatomy and stomatal response to environmental conditions, T c was compared with midday stem water potential ( s ) measurements. In persimmon trees, leaf stomatal conductance (g s ) was also measured. T c was the most sensitive indicator of plant water status particularly due to the lower tree-to-tree variability as compared to  s and g s . On the other hand, in citrus trees T c was not always affected by plant water stress. Only in the second experimental season, when air vapour pressure deficit values were below 2.7 kPa and images were also taken from above the canopies, deficit-irrigated trees had higher T c than the control ones, this difference being at most 1.7 ºC. Overall, the results show that hand-operated thermographic cameras can be used to detect plant water stress in both fruit tree species.Nevertheless, the use of T c measurements to detect plant water stress appears to be more precise in persimmon than in orange citrus. This might be because persimmon trees have larger leaf size which determines higher canopy resistance allowing for higher increases in canopy temperature in response to water stress via stomatal closure.3

Selecting Canopy Zones and Thresholding Approaches to Assess Grapevine Water Status by Using Aerial and Ground-Based Thermal Imaging

“…The differences between sunlit and shadow zones with FRT and SDM coincided with those obtained by Jones et al [21], who found that the shadow side of the canopy was particularly appropriate for row or tree crops. In the case of nadir view, the results obtained with the EBT and FRT filters coincided with those obtained by Ballester et al [40], who found that significant differences were detected in the nadir zone between stressed and non-stressed plants when lateral images did not detect differences between them. However, Ochagavia [19] found that r 2 values in vineyards with temperature values recorded from the lateral canopy side were higher than temperature values measured from the nadir position.…”

Canopy temperature variability in a tropical rainforest, subtropical evergreen forest, and savanna forest in Southwest China

“…Wang & Gartung (2010) found that the midday Tc-Ta in a water-stressed, deficit irrigation treatment of peach trees were in the range 5-7 °C. The maximum Tc difference between deficit-irrigated and control trees observed in persimmon trees was 4°C (Ballester et al 2013), while the maximum Tc difference between drought year and normal year was about 1 °C in the TRF. The possible reasons for the lower Tc-Ta found in the tropical rain forest include: (i) tree species in the tropical rain forest are highly diversified in canopy architecture.…”

“…The temperature of the branches and selfshaded leaves were not measured, resulting in an underestimation of the actual Tc. This might be a general problem in natural forests (Scherrer et al 2011). (ii) Most studies dealing with drought effects on Tc on crops have worked with precise irrigation treatments for determining the Tc to the difference in drought stress level, such as irrigated 50% evapotranspiration and irrigated 25-33% (Campbell & Norman 1990, Wang & Gartung 2010, Ballester et al 2013. Therefore, the Tc of crops might be more sensitive to severe drought stress in the irrigation treatments.…”

“…Infrared Tc measurements are automatic and effective, providing an alternative option to conventional methods such as stomatal conductance or stem water potential measurements in monitoring plant water status (Jackson 1991, Jones 1999, Wang & Gartung 2010, Ballester et al 2013.…”

“…Another study demonstrated that Tc has great responsiveness to variations in water status of persimmon trees (Ballester et al 2013): the Tc response to water stress was different for each experimental season. In a year with normal water availability (2009), Tc did not allow detection of the existing differences in plant water status, but during a drought year (2011), water stressed trees had significantly higher Tc than control trees with differences of up to 1.7 °C (Ballester et al 2013).…”