Thermography studies of the spatial and temporal variability in stomatal conductance of Avena leaves during stable and oscillatory transpiration

The spatial and temporal distribution of stomatal conductance of young Avena sativa cv. Seger leaves was studied when the whole-leaf transpiration was stable or displayed complicated oscillatory behaviour to determine whether different regions of the leaf behaved synchronously. A camera detecting infrared radiation in the 7.5-13 mum range was used to capture leaf temperature images which represented an indirect measure of the transpiration. Simultaneous gas exchange measurements of whole-leaf transpiration were also recorded. During nonoscillatory behaviour of whole-leaf transpiration, nonhomogeneous, patch-like temperature distributions across the leaf surface could sometimes be observed. However, during complex oscillatory behaviour or dampening of the oscillations, the entire leaf surface displayed the same temporal leaf temperature pattern as the whole-leaf transpiration. Small phase differences characterized by distal regions lagging 0.5-3 min behind the central leaf region were observed. The synchronous behaviour observed during oscillatory transpiration indicates strong coupling between stomata. During stable whole-leaf behaviour, the coupling was weaker and temperature distributions similar to results categorized as patchy stomatal conductance could be observed.