Optimizing thermal imaging as a technique for detecting stomatal closure induced by drought stress under greenhouse conditions

Temperature of leaves or canopies can be used as an indicator of stomata] aperture, which is considered a sensitive response to soil water deficit. In this paper we analyse the robustness and sensitivity of thermal imaging for detecting changes in stomata] conductance and leaf water status in a range of plant species. Thermal imaging successfully distinguished between irrigated and non-irrigated plants of a variety of species under greenhouse or controlled chamber conditions, with strong correlations between thermal indices and stomatal conductance measured by porometry. Our results also highlighted issues that need to be addressed in order to be confident of always detecting drought stress using this technique. These include variability in leaf angles and the limited reliability of 'wet' and 'dry' leaves to represent leaves with stomata fully open or stomata fully closed. These results should assist the design of protocols for application in crop production or ecosystem monitoring.