When a cuvette is not a canopy: A caution about measuring leaf temperature during gas exchange measurements

Plant gas exchange systems are widely used to study leaf physiological processes and properties such as stomatal function and the maximum carboxylation rate of Rubisco. Increasingly, these systems are used to assess how leaf gas exchange varies with temperature in order to better understand how rising temperature will impact plant function. Examples of such studies include variation in optimal temperatures of photosynthesis as a function of species and growth environment, and respiratory acclimation to higher temperatures. Leaf thermoregulation leading to homeothermy has been reported based on leaf gas exchange measurements spanning a large (similar to 25 degrees C) temperature range. However, as we show here, the design of a popular gas exchange system used for temperature-response measurements can lead to biased measurements of leaf temperature. We demonstrate this with an example showing that apparent leaf thermoregulatory behavior can arise even in empty cuvettes. More broadly, our results have implications for other temperature manipulations in similar gas exchange systems.