Effect of leaf temperature on estimating physiological traits of wheat leaves from hyperspectral reflectance

A growing number of leaf traits can be predicted from hyperspectral reflectance data. These include structural and compositional traits, such as leaf mass per area, nitrogen and chlorophyll content, but also physiological traits such a Rubisco carboxylation activity, electron transport rate and respiration rate. Since physiological traits vary with leaf temperature, how does this impact on predictions made from reflectance measurements? We investigated this with two wheat varieties, by repeatedly measuring each leaf through a sequence of temperatures imposed by varying the air temperature in a growth room. The function predicting Rubisco capacity normalised to 25 °C predicted the same value, regardless of leaf temperatures ranging from 20 to 35°C. Leaf temperature affected none of the predicted traits: V cmax25 , J, chlorophyll content, LMA, N content per unit leaf area or V cmax25 /N. However, as others have derived models to predict Rubisco activity that includes variation associated with leaf temperature, we discuss whether these functions may include a temperature signal within the reflectance spectra.