Challenging the water stress index concept: Thermographic assessment of Arabidopsis transpiration

Abstract

Water stress may greatly limit plant functionality and growth. Stomatal closure and consequently reduced transpiration are considered as early and sensitive plant responses to drought and salinity stress. An important consequence of stomatal closure under water stress is the rise of leaf temperature (Tleaf), yet Tleaf is not only fluctuating with stomatal closure. It is regulated by several plant parameters and environmental factors. Thermal imaging and different stress indices, incorporating actual leaf/crop temperature and reference temperatures, were developed in previous studies toward normalizing for effects unassociated to water stress on Tleaf, aiming at a more efficient water stress assessment. The concept of stress indices has not been extensively studied on the model plant Arabidopsis thaliana. Therefore, the aim of this study was to examine the different indices employed in previous studies in assessing rosette transpiration rate (E) in Arabidopsis plants grown under two different light environments and subjected to salinity. After salinity imposition, E was gravimetrically quantified, and thermal imaging was employed to quantify rosette (Trosette) and artificial reference temperature (Twet, Tdry). Trosette and several water stress indices were tested for their relation to E. Among the microclimatic growth conditions tested, RWSI1 ([Trosette − Twet]/[Tdry − Twet]) and RWSI2 ([Tdry − Trosette]/[Tdry − Twet]) were well linearly‐related to E, irrespective of the light environment, while the sole use of either Twet or Tdry in different combinations with Trosette returned less accurate results. This study provides evidence that selected combinations of Trosette, Tdry, and Twet can be utilized to assess E under water stress irrespective of the light environment.

Non‐invasive monitoring of tomato graft dynamics using thermography and fluorescence quantum yields measurements

“…This minimises the effect of variability derived from factors such as variations in air vapour pressure deficit, differences in plant leaf surfaces or even changes in the orientation of the sampled leaves (Maes & Steppe, 2012; Costa et al, 2013). It is, therefore, appropriate to use plants cultivated in growth chambers with controlled environmental variables (Savvides et al, 2022). In our study, infrared thermal images showed clear changes in leaf temperature (Figure 2A) and, therefore, in inferred transpiration during graft healing.…”

“…Scale‐up of the technique presented here has high potential to improve the yield of grafted tomato (and analogous crops). However, to achieve this, several recommendations should be taken into account: to be effective, thermography for monitoring transpiration requires that the environmental conditions should be controlled to the greatest extent possible, trying to take the measurements at the same hour of the day and avoiding the effect of wind or variations in light or humidity (Poirier‐Pocovi & Bailey, 2020; Savvides et al, 2022). If applying this method to plants grown in a greenhouse, then thermography should be used in sunny conditions and on plants in well‐watered substrates (Poirier‐Pocovi & Bailey, 2020; Vialet‐Chabrand & Lawson, 2020).…”

“…Twenty plants were used to infer leaf transpiration dynamics using a thermographic camera (C3, FLIR‐MSX) vertically positioned 30 cm above each plant. The emissivity value was set at 0.95 (Jones, 2004; Savvides et al, 2022). The plants were taken out of the healing chamber and placed on a laboratory workbench close to the culture chamber.…”

“…It is advisable to standardise leaf temperature measurements, always photographing perpendicular to the leaf and at the same distance, and introducing reference temperatures to control for sensitivity to ambient conditions such as radiation, air temperature, humidity, etc. (Jones et al, 2009;Savvides et al, 2022;Vialet-Chabrand & Lawson, 2020).…”

Gas exchange and photochemical efficiency of guava under saline water irrigation and nitrogen-potassium fertilization

“…From an ECw of 2.6 dS m -1 for combination C1 and 1.6 dS m -1 for C3, there was a reduction in transpiration (Figure 3A), i.e., activating a plant defense mechanism associated with stomatal closure (Figure 2A). Transpiration is a process in which energy in the form of latent heat is transferred from the leaf to the air, being a mechanism of acclimatization of the plant to stress (Savvides et al, 2022). Pinheiro et al (2022) mention that there is a close relationship between gs and E because the flow of water vapor to the atmosphere decreases when the stomata are closed, thus triggering a process of reduction in transpiration due to the decrease in stomatal conductance.…”